Physical Activity and Depression: With a Attention to Research Among Adolescent Girls

8/6/2019 Physical Activity and Depression: With a Attention to Research Among Adolescent Girls

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Running Head: PHYSICAL ACTIVITY AND DEPRESSION 1

Physical Activity and Depression:

With Attention to Research Among Adolescent Girls

Margae Knox

University of California, Berkeley





PHYSICAL ACTIVITY AND DEPRESSION 3

Physical Activity and Depression: With Attention to Research Among Adolescent Girls

Introduction

Depression Prevalence and Characteristics

Major depressive disorder is strikingly common. It is characterized by the presence of

five or more of the following symptoms: depressed mood, diminished interest or pleasure in all

or most activities, significant weight loss or weight gain with change in appetite, difficulty

sleeping or excessive sleeping, slow movement observed by others, fatigue or loss of energy,

feelings of worthlessness or excessive guilt, diminished ability to concentrate or make decisions,

and recurrent thoughts of death. Symptoms occur most days during the past two weeks and areunaccounted for by other circumstances such as loss of a loved one: (American Psychiatric

Association Task Force on DSM-IV, 2000). In a national survey, 17.1% of people ages 15-54 in

the United States indicated they had experienced a lifetime prevalence of depression; 4.9% of

respondents indicated they currently were experiencing depression (Blazer, Kessler, McGonagle,

& Swartz, 1994). An updated version of this survey, quoted by the CDC ( Morbidity and

Mortality Weekly Report, 2010), found a 16.2% lifetime prevalence for major depression with a

6.6% 12-month prevalence (Kessler et al., 2003).

“Mental illness is not a trivial issue […] rather, it is as common as high blood pressure

and much more common than heart attack and stroke” (Biddle & Mutrie, 2001, p. 205).

According the World Health Organization, depression is the fourth leading contributor the global

burden of disease and the second leading cause of disability among 15-44 year olds (2011).

Worldwide, depression is about two times more prevalent in women compared to men. Research

indicates the higher female prevalence is due to greater first-onset among women, not differential

length, recurrence frequency, or help seeking patterns.




Because depression typically emerges in adolescence and can recur throughout life, it is

important to better understand symptoms, prevention and treatments among this age group

(Kessler, 2003). According to Birmaher et al.’s review, the prevalence of current depression in

children varies between 0.4% and 2.5% but in adolescence the range increases to between 0.4%

and 8.3% (1996). During adolescence, the estimate of lifetime depression prevalence increases to

between 15% and 20%, comparable to proportions found in the adult population. (Birmaher et

al., 1996; Blazer et al., 1994; Kessler et al., 2003). The Oregon Adolescent Depression Project, a

survey of 1709 high school students ages 14 to 18, found a 2.9% point prevalence and 20.4%

lifetime prevalence the first year. The year’s incidence—the percentage of subjects not initiallydepressed that developed depression—was 7.8%. (Lewinsohn, Rohde, & Seeley, 1998). Though

boys and girls experience nearly equal levels of depression in childhood, beginning about age

thirteen depression levels in girls significantly increase compared to boys and soon reach the

two-to-one ratio observed in adulthood (Twenge & Nolen-Hoeksema, 2002). Female gender is a

key risk factor for both earlier onset and greater prevalence of depression.

Physical Activity and Depression Correlations

Studies in adult populations typically find an inverse relationship between physical

activity levels and depression. Physical activity is any bodily movement that engages muscles

and uses more energy than when resting. Physical activity, in contrast to exercise, need not be

planned or structured (National Heart, Lung, and Blood Institute, May 2009). The American

College of Sports Medicine claims “Regular physical activity is associated with improved levels

of psychological well being,” and assigns this statement an evidence category A/B, indicating

overwhelming/substantial evidence with strong, but sometimes inconsistent evidence from

randomized control trials and observational studies (Chodzko-Zajko WJ et al., 2009). Physical




activity and depression is a growing area of study and an understanding of the relationship

between physical activity and depression is continually improving.

The first large prospective study that pointed to physical inactivity as a risk factor for

depression symptoms was the Epidemiologic Follow Up Study (1982-1984) to the first National

Health and Nutrition Examination Survey (NHANES I). Self reported data from 1,900 healthy

subjects, 25-77 years old, revealed a cross-sectional association between little or no physical

activity and greater depression symptoms. The study’s analysis, which excluding women

depressed at baseline, found that initial physical activity levels were an independent predictor of

depression at follow-up eight years later. Women who participated in little or no recreationalactivity were two times more likely than women with much or moderate physical activity to

develop depression symptoms at follow up (Farmer et al., 1988.) In a foundational meta-analysis

of physical activity and depression studies, North, McCullagh, and Tran examined 80

experimental studies (1990). The effect sizes calculated for each individual study ranged from

-3.88 to 2.05. But overall, a statistically significant mean effect size of -.53 was calculated,

indicating that depression levels among exercise treated groups were about one-half a standard

deviation lower than control groups (North et al., 1990). While these meta-analysis findings are

noteworthy they should be observed cautiously due to concerns about the methodological quality

of included studies and whether statistically combining the effect sizes is appropriate given the

large variety of study designs and populations (Biddle & Mutrie, 2001, p. 212).

Nevertheless, the literature to date provides a credible link between physical activity and

depression outcomes. The nine classic epidemiology criteria for determining whether an

association exists between an illness and an environmental condition are strength of association,

consistency of observed association, specificity of effect, temporal sequencing, dose-response




relationship, biological plausibility, coherence with current understanding, experimental support,

and existence of analogous associations (Hill, 1965). The physical activity and depression

association generally meets seven these nine criteria, the exceptions being a dose-response

relationship and specificity (Biddle & Mutrie, 2001, pp 217-219).

Physical Activity and Depression in Adolescents

Although the relationship between physical activity and depression is less studied in

adolescents than adults, there are noteworthy observations and experiments. Very broadly,

physical activity levels substantially drop during the adolescent years, the same age range where

depression increases. During school-age years, activity levels decline 2.7% per year in males and7.4% per year in females (Pate, Long, & Heath, 1994). Between the ages 12 to 21, physical

inactivity increases 10.4% in males and 11.2% in females while regular vigorous activity

decreases 28.6% in males and 36.0% in females (Caspersen, Pereira, & Curran, 2000). At the

same time, depression among adolescents increases from a childhood point prevalence of 0.4-

2.5% (Birmaher et al., 1996) to nearly an adult point prevalence of around 4.9% (Blazer et al.,

1994). In a review by Calfas and Taylor, nine out of eleven studies addressing depression had a

positive benefit relationship with physical activity (1994).

In general, studies that examine the relationship between physical activity and depression

in adolescents have mixed findings. A study in London involving 2,789 students in grades seven

and nine found that every additional hour of exercise per week was associated with an 8%

decreased odds of depressive symptoms. A follow up survey, which included 75% of the original

population, found a consistent trend, but failed to maintain a statistically significant association

(Rothon et al., 2010).




One of the first experimental studies of aerobic exercise and depression in adolescents

was a 9-week trial conducted among 27 patients in a private psychiatric facility. A high attrition

rate resulted due to discharge from the facility. Only eleven subjects, four boys and seven girls,

completed the study. The treatment group received extra running/aerobic classes three times per

week while the control group participated in only the usual physical activity program at the

facility. Treated girls’ depression scores consistently decreased though treated boys’ depression

scores did not, but the measurements are too variable and the sample sizes too small to draw

meaningful conclusions (Brown et al., 1992). Overall, differences between treatment and control

groups were not statistically significant (Brown, Welsh, Labbe, Vitulli, & Kulkarni, 1992; Larun, Nordheim, Ekeland, Hagen, & Hein, 2009).

More recently, an analysis of physical activity and depression used information from the

TEENS (Teens Eating for Energy and Nutrition at School) study, a prospective survey that

annually assessed 4,595 total middle-school students between the start of seventh grade and the

conclusion of eighth grade. The study examined a correlation between Center for Epidemiologic

Study Depression (CES-D) scores and the question “Do you get some regular physical activity

outside of school? By regular we mean at least 3 times a week for at least 20 minutes at a time.”

Responses to this question ranged on a five-point scale, with five indicating “most of the time”

and one indicating “never”. A modest relationship emerged such that higher initial levels of

depression were associated with lower scores of physical activity and reductions in physical

activity over time were associated with increasing depression. Quantitatively, one standard

deviation change in the measurement for physical activity frequency was correlated an inverse

.25 standard deviation change in depression symptoms. (Motl, Birnbaum, Kubik, & Dishman,

2004). Alternatively, a survey of 727 adolescents in grades 7-12 found no significant association




between accumulated duration of moderate to vigorous physical activity and severity of

depressive symptoms. A relationship between participation in sports or lessons and depression

severity was also considered, but only an association among boys and not among girls was found

(Desha, Ziviani, Nicholson, Martin, & Darnell, 2007). These various studies are informative but

limited, and the possible relationship between physical activity and depression in adolescents

still requires further exploration. Studies of physical activity depression among adolescent

females are particularly important because depression risk factors and outcomes among females

may differ compared to males.

Hypotheses

HPA Axis & Cortisol

A number of mechanisms could potentially contribute to or help explain a possible

relationship between physical activity and depression. The HPA—hypothalamic-pituitary-

adrenal—axis, which regulates cortisol secretion, is one possible mechanism. Approximately

50% of depressed patients exhibit a hyperactive HPA axis (Southwick, Vythilingam, & Charney,2005). The HPA axis begins with secretion of CRH—corticotrophin-releasing hormone—from

the hypothalamus. CRH in turn causes the anterior pituitary to release ACTH—

adrenocorticotropic hormone—which then stimulates cortisol production from the adrenal

glands. (Davies, Blakeley, Kidd, & McGeown, 2001) In acute, regulated amounts, cortisol is

responsible for desirable adaptive responses; it is “essential for optimal functioning of virtually

all tissues” (Davies et al., 2001). However, chronically high levels of cortisol are harmful to

physical and mental health (Southwick et al., 2005). There are several possible associations

between HPA activity and depression although researchers still do not fully comprehend this

complex relationship. Overall, more severe depressive symptoms are associated with increased




secretion of cortisol, also known as hypercortisolism (Angold, 2003). Gold et al. claim that the

evidence suggests hypercortisolism in depressed people is due to a defect at or above the

hypothalamic level, but this hypothesized defect’s precise nature, including the direction of

causation, is unknown (Gold, Goodwin, & Chrousos, 1988). It is also possible that

hypercortisolism is primarily just an indicator of stressful life events that lead to depression.

Further, hypercortisolism is not present in every case of depression and it is rarely observed in

children. Though depressed adolescents typically do not exhibit constant hypercortisolaemia,

they do often have elevated cortisol levels before sleep onset, a time when the HPA axis is

usually more at rest (Angold, 2003).Exercise may improve depression in part by regulating the HPA axis response to stress

(Brosse, Sheets, Lett, & Blumenthal, 2002). Very generally, about half of studies reviewed by

Gerber and Puhse indicated that people with high exercise levels exhibit fewer health problems

when exposed to stress (2009). More specifically, a study comparing sedentary persons to

moderately and highly trained athletes examined subjects’ HPA axis activation, measured by

plasma ACTH after weekly treadmill exercises. Exercises were performed at 50% VO2

maximum the first session, 70% the second, then 90% the final session. Trained and sedentary

subjects had equal HPA axis activation at equal percentages of maximum oxygen uptake levels,

but trained subjects required a greater absolute amount of oxygen consumption to equally

activate the HPA axis (Luger et al., 1987). However, it is not possible to say whether the

athletes’ lower HPA activity at equal absolute workloads generalizes to lower HPA activity

given equal life stressors. Additionally, the specific HPA changes in response to physical

training are uncertain. A study of trained male athletes compared to moderately athletic males

found elevated plasma ACTH levels, but no difference in cortisol levels was found in the trained




athletes, suggesting that exercise training may lessen adrenal response to ACTH (Wittert,

Livesey, Espiner, & Donald, 1996). It is still unknown how these findings correspond with

depression levels and whether findings can be generalized to adolescents.

Neurotransmitters

Neurotransmitters are a second biological pathway related to depression. Most studies

have focused on seratonin and norepinephrine, the first neurotransmitters linked to mood. In the

1950’s, a connection between neurotransmitters and mood was serendipitously discovered when

a hypertension treatment, reserpine, led to depression in about fifteen percent of treated patients.

Investigation found that reserpine depletes norepinephrine and the serotonin precursor 5-HT bydamaging intracellular storage. The damage also makes norepinephrin and 5-HT degradation

more likely. Soon after this discovery, elevated mood was observed in isoniazid-treated

tuberculosis patients. Isoniazid inhibits norepinephrine and 5-HT degradation. Together, these

findings led to the hypothesis that higher monoamines levels are related to increased mood

(Dunn & Dishman, 1991, p. 57).

Supporting this neurotransmitter hypothesis, depressed patients typically have low levels

of the main serotonin metabolite 5-HIAA in measurements from cerebral spinal fluid.

Pharmacologic studies initially focused on drugs inhibiting norepinephrine uptake, and

simultaneously inhibited serotonin uptake, in order to elevate neurotransmitter levels. Research

efforts have since shifted from norephinephrine to serotonin since it has been shown that drugs

such as Prozac that only inhibit serotonin uptake are equally effective (Ganong, 2005, p. 262-

263). While original hypotheses about neurotransmitter mechanisms have been revised several

times as research has advanced, a consensus remains that monoamines are related to depression

(Dunn & Dishman, 1991, p. 57; Morgan, 1985).




Theoretically, like pharmacologic treatments for depression, exercise could increase

levels of brain norepinephrine and 5-HT; but this assumption is mostly speculative (Morgan,

1985). Evidence linking neurotransmitters and physical activity is limited. Whole brain

norepinephrine has been found to decrease with acute exercise episodes but increase in response

to repeated, chronic exercise (Dunn & Dishman, 1991, p. 69). In both trained animals and

humans, short-term physical activity increases blood concentrations of tryptophan, a building

block of serotonin (Chaoulaoff, 1997, p. 182). Acute physical activity may also increase

synthesis and/or release of 5-HT but conclusive statements cannot be made without more

research (Chaouloff, 1997, p. 188). Exercise studies in animal models of depression couldtremendously help to further understanding of interactions between depression-like behavior,

exercise and neurotransmitters (Dunn & Dishman, 1991). One animal model experiment found

that compared to sedentary mice, mice that were allowed activity wheel exercise had statistically

significant lower escape latency after uncontrollable foot shocks, suggesting exercise might

buffer depression in response to stress. This experiment also showed statistically significant

higher levels of norepinephrine in the brain’s locus coeruleus among activity wheel mice

compared to sedentary mice (Dishman et al., 1997).

It is unclear how neurotransmitters interact with the HPA axis and hormone systems.

Researchers have suggested that norepinephrine produces both stimulatory and inhibitory effects

on the HPA axis. Both of these contrasting propositions could be true. Norepinephrine likely

produces different effects at different levels of the HPA axis (Dunn & Dishman, 1991, p. 66).

Meanwhile, one study concluded that HPA hyperactivity does not seem related to serotonin

dysfunction (Molcrani, Duval, Crocq, Bailey, & Macher, 1997).




Neurotransmitters and the HPA axis also interact with steroid hormones in a delicately

balanced manner. For example, ACTH from the pituitary stimulates adrenal androgen secretion

(Davies et al., 2001, p. 441). And, higher levels of estrogen at puberty can alter neurotransmitter

sensitivity (Steiner, Dunn, & Born, 2003). It is still unclear how the dramatic hormone changes

associated with menarche might contribute to the increases in depression incidence observed at

about the same time. Steiner et al. propose that the hormonal changes associated with menarche

require the HPA to mature to become sensitive to new feedback mechanisms. This adjustment

period may increase the vulnerability of the HPA axis to psychosocial stress (2003). Better

identification of these interactions could be very influential for the evaluation and treatment of depression in adolescent girls.

Sleep

Sleep abnormalities are both a symptom of depression and a risk factor. About 90% of

depressed patients report sleep disturbances (Mendelson, Gillin, & Wyatt, 1977). In a

prospective study, among those that developed major depression, the odds of insomnia were 39.9

times the odds of insomnia among those that did not develop depression (Ford & Kamerow,

1989). Studies typically define a sleep cycle as four progressively deeper stages of slow-wave

sleep that then regress to the original stage and are followed by the very light, rapid eye

movement (REM) stage (Driver & Taylor, 1996). Subjects with primary depression often exhibit

a shortened REM latency, i.e., a reduced time period until REM sleep is initiated (Kupfer, 1976).

Additionally, several but not all sources suggest that an increased REM latency is correlated with

depression remission. Increased REM latency is observed with many antidepressant medications

(Riemann Berger, & Voderholzer, 2001). In a review of studies among children and adolescents,

depressed subjects compared to controls exhibited statistically significant shortened REM




latency in seven of thirteen sleep studies. Five studies showed that depressed subjects had

statistically significant increases in sleep onset latency, the time to fall asleep. There were no

statistically significant differences in slow wave sleep measures (Riemann et al., 2001).

Exercise may impact sleep a number of ways. In a random sample of 200 middle-aged

men and women, one third felt that exercise positively impacts sleep, with the most common

reports including improved ease falling asleep, deepness of sleep, sense of well-being and

morning wakefulness (Vuori, Urponen, Hasan, & Partinen, 1988). The extent to which research

supports these common perceptions is mixed. In general, morning exercise has little affect on

sleep, while afternoon exercise increases slow-wave sleep, delays onset of REM, and shortensthe REM stage (Driver & Taylor, 1996; Youngstedt, O'Connor, & Dishman, 1997). Kubitz et al’s

meta-analysis calculated effect sizes for both acute and chronic exercise studies in order to

determine the immediate effects of exercise on sleep and the effects of long-term exercise on

sleep. The overall meta-analysis did not account for the time of day exercise was conducted, but

in both acute and chronic exercise studies exercising individuals fell asleep faster and slept

slightly longer and deeper (1996). In one of few adolescent studies of exercise and sleep Brand et

al. compared high-exercising and low-exercising adolescents, with mean exercise durations of

8.5 and 2.5 hours per week respectively. The study found that high exercisers had more slow-

wave sleep, less light and REM sleep, and lower depressive scores (2010).

Methodological concerns of most sleep studies include small sample sizes. A small

sample size reduces the statistical power, the ability to ascertain whether observed effects are

real (Kubitz et al., 1996). Studies of exercise’s effect on sleep typically only include samples

with good-sleepers so that exercise effects among populations with sleep disturbances, including

many cases of depression, remains undetermined (Kubitz et al., 1996; Youngstedt et al., 1997). It




is also unclear whether study results from adult populations can be generalized to adolescents; it

is likely that adolescent sleep patterns and responses to exercise significantly differ (Dahl et al.,

1996). Additionally, further exploration might examine whether sleep abnormalities are related

to endocrine abnormalities in depression (Riemann et al., 2001). Observations of HPA-axis

change just before and just after sleep onset supports a connection between hormones, sleep and

depression (Dahl et al., 1996)

Self-Esteem

While biological mechanisms are critical for explaining physical activity’s potential

antidepressant effects, cognitive explanations such as self-esteem are also worthwhileconsiderations. High self-esteem, especially in girls, appears to be an important element of good

mental and physical health (Park, 2003). Eckeland et al. discuss twenty-three studies of exercise

interventions on self-esteem in a literature review that was subsequently elaborated on in a report

by the Cochrane Collaboration. Meta-analysis of twelve of the twenty-three studies revealed a

small, statistically significant effect on self-esteem in favor of the exercise interventions, with

intervention and control groups differing by about a ten percent (Ekeland, Heian, Hagen, Abbott,

& Nordheim, 2004; Ekeland, Heian, & Hagen, 2005).

Although a direct relationship between actual physical fitness and self-esteem is

uncommon, a consistent relationship exists between perceptions of physical fitness and self-

esteem. Accordingly, intervention studies find that improved perceptions of physical fitness are

more strongly correlated to self-esteem than actual physical fitness improvement. Further, self-

esteem often improves before fitness effects have had time to take place (Sonstroem, 1984). A

study that compared self-esteem measures between a running group, a weight-training group, and

a delayed-treatment control group also supports this idea. Both the aerobic and weight-training




groups experienced significant self-esteem improvements compared to the control group. The

aerobic and weight training subjects also both perceived themselves as having improved fitness,

but neither group showed improved treadmill test performance (Ossip-Klein et al., 1989, p. 160).

Another relevant study compared a ten-week exercise program divided into two exercise groups

of 24 subjects each. In one group instructors emphasized anticipated improvements in both

aerobic capacity and psychological well being, and in the other group instructors were equally

enthusiastic but only focused on the exercise program’s biological aspects. Both groups

experienced improved self-esteem, but the group primed by instructors to expect psychological

improvements had significantly greater scores (Desharnais, Jobin, Cote, & Levesque, 1993)During the developmental stage of adolescence, physical activity success may be

particularly meaningful for improving self-esteem (Calfas & Taylor, 1994). Physical Activity

Epidemiology lists a loss of self-esteem as one of several etiologic factors of depression, but

studies have not identified precisely how self-esteem contributes to the lower rates of depressive

symptoms in physically active people (Dishman, Washburn, & Heath, 2004, p. 311 & 327).

Theoretically, physical activity will enact self-esteem improvements through a cycle of positive

feedback between the skill development hypothesis of self-esteem and the self-enhancement

hypothesis. The skill development hypothesis proposes that successful experiences make an

individual feel good about herself, and the self-enhancement hypothesis is the idea an individual

will act based on her perception of herself. As a person perceives successes from time spent in

physical activity, she will continue to pursue those activities. And, as physical activity makes her

feel good about herself, self-esteem is continually enhanced and the cycle perpetuated

(Sonstroem, 1997, p. 128-129). Additional features of physical activity that possibly contribute

to improved self-esteem include: increased sense of competence, skill mastery, goal




achievement, feelings of somatic well-being, social experiences (Sonstroem, 1997, p.129),

favorable comments by friends, and distraction from stressful stimuli (Morgan, 1985).

Most studies that examine a relationship between physical activity and self esteem focus

on the relatively stable, one-dimensional global self-esteem, which, according to Sonstroem, has

hindered self-esteem research. More recent models of self-esteem advance a hierarchical nature

of self-esteem: the global self-esteem is comprised of several domain-specific esteems and sub-

domains (Sonstroem, 1997). For example, physical self-esteem is a domain of global self-esteem

and associated sub-domains include physical strength, attractive body and sports competence

(McAuley, Mihalko, & Bane, 1997). While global self-esteem relates to overall psychologicalwell-being, domain specific esteem is more predictive of actual performance. This distinction is

important because it explains why self-esteem studies often report weaker associations than

might be expected (Rosenberg, Schooler, Schoenbach, & Rosenberg, 1995) McAuley’s analysis

of physical fitness and self-efficacy in a 20-week exercise program among middle-aged adults

reflects how the domain level influences self-esteem measures. Self-efficacy change was greatest

at the sub domain level for physical condition, mid-level at the physical esteem domain level,

and least at the global level. As understanding of how physical activity and self-esteem interact

develops, researchers also gain understanding toward reducing depression (McAuley et al.,

1997).

Methods

Studies for closer review to assess the relationship between physical activity and

depression in adolescent girls were gathered through a PubMed search. The search term

“physical activity and depression” was used with the limits “Female” and “Adolescent: 13-18

years.” The search details generated were: “(("motor activity"[MeSH Terms] OR ("motor"[All




Fields] AND "activity"[All Fields]) OR "motor activity"[All Fields] OR ("physical"[All Fields]

AND "activity"[All Fields]) OR "physical activity"[All Fields]) AND ("depressive

disorder"[MeSH Terms] OR ("depressive"[All Fields] AND "disorder"[All Fields]) OR

"depressive disorder"[All Fields] OR "depression"[All Fields] OR "depression"[MeSH Terms]))

AND ("female"[MeSH Terms] AND "adolescent"[MeSH Terms])” 410 results were returned.

Articles were then browsed for titles that directly addressed the relationship between physical

activity and depression in an adolescent female population.

Results

Three studies from the PubMed search—a cross-sectional study, a prospective study, anda randomized control trial—met the criteria for this literature review, directly addressing the

relationship between physical activity and depression in an adolescent female population. The

search results also returned findings about depression and physical activity more generally,

including three studies described previously that examined a relationship between physical

activity and depression among both male and females (Brown et al., 1992; Desha LN et al.,

2007; Motl et al., 2004). In summary, significant relationships emerged between physical activity

and depression in two of the three studies discussed below. Each study acknowledges a

relationship between physical activity and depression could also reflect unmeasured factors

associated with physical activity such as social connections, skill-mastery, and distraction. Two

of the three studies assume a relationship in which physical activity impacts depression (Johnson

CC et al., 2008; Nabkasorn et al., 2006), but the relationship may also be bi-directional (Jerstad

SJ et al., 2010).

Study One




Depressive Symptoms and Physical Activity in Adolescent Girls (Johnson CC et al.,

2008). The objective of this study was to evaluate the relationship between depressive symptoms

and physical activity in a geographically and ethnically diverse sample of sixth grade adolescent

girls. The study built on the National Heart, Lung, and Blood Institute’s TAAG (Trial of Activity

of Adolescent Girls) study, whose goal was to design and evaluate and intervention that would

reduce the physical activity decline in middle school girls by half. Each of six different field

centers—Universities of Arizona, Maryland, Minnesota, and South Carolina; San Diego State

University and Tulane University—collected data from six different schools, resulting in 36

geographic and ethnically diverse schools included in the study. Before schools in the TAAGstudy were randomized into treatment and control conditions, baseline measurements were made.

Sixty girls from each site were randomly selected to be recruited for the TAAG study and 1,721

(80%) agreed. Of these, 1,397 girls had complete measurements for all three variables required

in this study.

The three baseline measurements of special interest to the current study are the Center for

Epidemiology Study Depression scale (CES-D), MTI ActiGraph Accelerometer data, and the

3DPAR (3-Day Physical Activity Recall) survey. The CES-D scale is a twenty-item

questionnaire with responses ranging on a four-point scale from “rarely” to “almost always.” The

CES-D has been standardized, has high to acceptable internal validity, and is used extensively in

research with adolescents and adults. Although it is not a diagnostic tool, a score greater than 16

in adults and greater than 24 in adolescents has been used to signal depression. An accelerometer

is like a sophisticated pedometer to measure physical activity levels. An accelerometer is able to

detect acceleration and deceleration and record the time of day, providing data on the

vigorousness and intervals of physical activity. The 3DPAR is a self-report survey that asks




participants to recall their activities for every thirty minutes over the past three days. The 3DPAR

has been validated against pedometer counts and accelerometer counts. Other measurements that

were noted and adjusted for in analysis include BMI and a questionnaire of demographics,

attitudes toward physical activity, social support, and barriers to physical activity.

This study generated both mixed-model linear and mixed-model logistic regressions

relating physical activity and CES-D. The linear model treated CES-D score as continuous

variable while the logistic regression model treated CES-D score as a binary variable based on a

cut of score of 24. The study separately analyzed nine categories of physical activity ranging

from sedentary to vigorous activity. Five of these categories came from the accelerometer datameasurements and four from the 3DPAR survey measurements. With the exception of sedentary

activity, neither linear nor logistic regressions revealed a relationship between physical activity

measures and CES-D scores. In the linear model, sedentary behavior measured by accelerometry

indicated a modest, statistically significant inverse correlation with depression; i.e., every

additional minute of sedentary behavior yielded a .00987-point decrease in CES-D scores

suggesting very slightly improved depression. A two standard deviation increase in sedentary

behavior in this sample would predict a 1.35-point decline in CES-D scores. However the

authors acknowledged that the inverse relationship between sedentary behavior and depression

might be a statistical anomaly, an artifact of the fact sedentary behavior was high while CES-D

scores generally were not.

One of this study’s strengths was the combination of a more objective accelerometry

measurement for physical activity in addition to a self-report method. In combination, these

methods should have derived highly reliable physical activity measurements. The study reported

that on average the sample of girls engaged in an average of less than 24 minutes per day of




moderate and six minutes per day of vigorous physical activity. A review by Pate et al. concurred

that the majority of adolescent females were not meeting the guidelines for moderate to vigorous

physical activity, but differed with this study by suggesting that on average adolescents exercised

one hour a day, they just failed to do so three or more days a week (Pate et al., 1994). Perhaps

results differed because, in contrast to the studies reviewed by Pate et al, this study more

rigorously measured and more specifically classified physical activity.

Study Two

Prospective Reciprocal Relations Between Physical Activity and Depression in

Female Adolescents (Jerstad SJ et al.). This study sought to prospectively examine therelationship between physical activity and adolescents in order to test whether physical activity

reduces risk for future escalations of depression or whether depression reduces future physical

activity. Of the girls recruited, ages eleven to fifteen, 496 girls (56%) agreed to participate. Each

year throughout the six-year follow-up period the girls completed a questionnaire, participated in

structured interviews and had their height and weight measured. In addition to depression and

physical activity, other covariates of interest in this study were body dissatisfaction, bulimic

symptoms, social support, and body mass.

Depression was measured from structured interviews using the Schedule for Affective

Disorders and Schizophrenia for School-Age Children, a tool to assess whether subjects met the

Diagnostic and Statistical Manual of Mental Disorder criteria for major depressive disorder or

minor depression on a monthly basis over the past year. Physical activity was assessed with a

modified version of the Past Year Activity Scale, where subjects indicated the number of

activities they had participated in ten or more times during the past year.




Baseline physical activity predicted less depression over time. For each additional

physical activity participated in, the relative risk of later depression symptoms decreased one

percent; the relative risk of later minor or major depression decreased 8% and the relative risk for

later major depression decreased 16%. At the same time, the presence of depression symptoms

predicted reduced physical activity. Major depression decreased the likelihood of participating

on one additional physical activity the next year by 35% and minor depression decreased the

likelihood by 18%. All predictive effects adjusted for baseline depression and measured

covariates. Predictive effects were also all statistically significant.

Study Three

Effects of physical exercise on depression, neuroendocrine stress hormones and

physiological fitness in adolescent females with depressive symptoms (Nabkasorn et al.,

2006). This study attempted to address the current lack of experimental studies examining

psychological and physiological changes among depressed adolescents in response to physical

activity. The study used a crossover experimental design to evaluate the effects of an eight-week

exercise regimen compared to eight weeks of usual activity. Two hundred sixty six female

volunteers aged 18-20 were recruited for the study and evaluated for depressive symptoms.

Sixty-three participants presented mild to moderate depressive symptoms and did not meet the

exclusion criteria. Exclusion criteria included previously taken antidepressant medication,

symptoms of illness limiting physical activity, or engaged in regular, vigorous sports activity

during the prior six months. Fifty-nine participants agreed to participate. Originally, twenty-eight

subjects began with a physical activity while 31 subjects continued with their daily usual routine

as non-exercise controls. The physical activity program involved 50-minute group jogging

sessions performed at less than 50% maximal heart rate five days per week. After eight weeks,




the two groups switched roles. In the end 49 subjects—21 in the training first group and 28 in the

usual activity first group—completed the trial as prescribed and were included in analysis.

Every four weeks subjects completed the Center for Epidemiologic Study of Depression

(CES-D) scale, the main outcome measure in this study. At baseline and at eight-week intervals,

upon the conclusion of their respective exercise or usual activity period, subjects collected

separate 24-hour urine specimens to measure urinary cortisol and urinary epinephrine.

Specimens were sent to a laboratory where urinary cortisol was measured by radioimmunoassay

and urine epinephrine was measured by liquid chromatography. Additionally, at baseline and

eight-week intervals, measurements were made of lung capacity, heart rate and peak oxygenintake. Lung capacity was measured with a spirometer. Heart rate was measured while subjects

were seated for five minutes during the rest periods of an endurance test performed according to

the multistage YMCA submaximal exercise test protocol. Peak oxygen was estimated on the

basis of the heart rate increments to workloads during the endurance test.

In the training-first group CES-D scores significantly decreased during the first phase,

indicating improved depression, and then scores gradually rose during the regular daily activity

in the second phase. At the end of the second phase, however, CES-D scores continued to remain

significantly below baseline. The regular-daily-activity-first group had no significant changes in

any measurement during the first phase but significantly decreased CES-D scores during the

following exercise-training phase. Additional changes following the exercise training phase

included lower 24-hr urinary cortisol and norepinephrine secretions, lower heart rate at rest,

increased lung capacity, and increased peak oxygen uptake. No changes occurred following the

daily activity phase. Mean body weight did not significantly change during either phase.




Discussion

One of the challenges facing studies that examine physical activity and depression are the

limitations of physical activity and depression measurements. Both physical activity and

depression measurements regularly employ self-reported indicators such as surveys, which may

be inconsistent or unreliable. This is particularly true of surveys that are unique to a study and

have not been validated. Additionally, it is often difficult for surveys to fully capture the variable

of interest. For example, a physical activity survey that asks participants to rank their activity

levels from low to high cannot actually assess the actual number of minutes spent in physical

activity or the level of physical intensity.

Of the three studies only Johnson et. al., which collected accelerometry data, used an

objective physical activity measurement. This study did not find a relationship between physical

activity and depression. However it is possible that by dividing the physical activity data so

extensively any potential relationship between physical activity and depression was dampened.

Had measurements been analyzed as an accumulation as in other studies, a slight relation with

depression might have emerged. Although, like the relationship observed with sedentary

behavior, the potential relationship between physical activity and depression would likely be

modest and could also possibly be just an artifact of statistics.

The lack of a relationship between physical activity and depression demonstrated in this

study could also be due to many dependent variables that this study did not account for. This

study was thoughtfully designed, rigorously measuring physical activity, and even attempting to

adjust for factors associated with physical activity levels such as attitudes and social

environment. However, it is impossible to entirely account for activity factors that might

exacerbate or alleviate depression. For example, sedentary behavior might have shown a




correlation with improved depression because sedentary time was spent with an engaging book

or sitting down to a pleasant family dinner. Although findings from cross-sectional study designs

like this one are interesting, they are also limited because they cannot assess temporality or make

causal inferences. Longer-term and experimental designs will help to expand understanding of

the relationship between physical activity and depression.

Jerstad et al. expanded understanding of the relationship between physical activity and

depression by employing a prospective study design, which can give an indication of

temporality. Jerstad et al.’s results suggest both that participation in physical activities can be

protective against depressive symptoms and that depressive symptoms decrease the probabilityof participation in physical activities. As acknowledged in Johnson et al. and other studies,

several variables likely play a role in the relationship between physical activity and depression.

Jerstad et al. adjusted for four factors—body dissatisfaction, bulimic symptoms, social support,

and body mass—and still observed a modest but significant bidirectional relationship. However,

conclusions could be strengthened by using measures that assessed actual time spent in physical

activity levels and average amounts of energy expenditure, not just a measure of participation in

certain activities. It could be that some subjects are very active, but participate in few distinct

activities. Or in contrast, some subjects might dabble in several activities without exerting much

effort at any one.

A randomized control trial is considered the gold standard of scientific studies. In

Nabaksorn et al.’s randomized control trial a crossover design a cross-over design was used,

which has the advantage of potentially counterbalancing errors in randomization by exposing

both groups to treatment and control conditions. However, a drawback of crossover design is that

residual effects of the first phase may influence results in the second phase (Gordis, 2004, pp




140). One weakness of this study is that several subjects were not included in the final study

analysis. Five subjects dropped out and five subjects that were excluded because they failed to

maintain usual physical activity levels during the non-exercise phase. This 17% non-completion

rate but could have influenced results if data from those not included were systematically

different than those that properly completed the trial. For example, perhaps the low motivation of

the five-drop outs made them resistant to potential depression changes in response to physical

activity. It would also be interesting to find out how allowing subjects to participate that were not

included due to the exclusion criteria or changing the CES-D cut off score for inclusion would

have affected results.

Conclusions

Potential of Physical Activity as Treatment and Prevention for Depression

Research suggests that physical activity may be useful in treating depression, but

methodological weaknesses limit conclusions. Common weaknesses include small sample sizes,

inadequate blinding, and lack of intention-to-treat analysis (Lawlor & Hopker, 2001). Additionalconcern arises due to the limited external validity of depression studies. Exclusion criteria often

include previous medication use or experience with therapy and co-morbid disorders such as

anxiety and substance abuse, which disqualifies a large proportion of depressed outpatients

(Klein et al., 1985; Lawlor & Hopker, 2001).

One of the earliest studies considering physical activity as depression treatment compared

a running group to two psychotherapy treatments, one psychotherapy treatment time-limited and

the other time-unlimited. The authors concluded that running was at least as effective as

psychotherapy in alleviating moderate depression. However, the study design does contain

factors that may have influenced results. For example, psychotherapists were relatively




inexperienced compared to the running therapist and subjects in the running group spent more

time in treatment (Greist et al., 1979). Since then, four studies among depressed patients

comparing physical activity with cognitive therapy, a specific type of psychotherapy, have been

conducted and were meta-analyzed in a review by Lawlor & Hopker (2001). Overall, these four

studies showed a -0.3 standardized mean difference effect size for depression treated with

physical activity compared to cognitive therapy, suggesting slightly greater depression

improvement from physical activity. But the mean difference 95% confidence interval ranged

from -0.7 to 0.1, indicating neither treatment is significantly more effective than the other

(Lawlor & Hopker, 2001).The relative effectiveness of physical activity compared to medication treatments are also

of interest. One study explored physical activity compared to the anti-depressant medication

sertralin (Zoloft®) by dividing102 subjects into four categories: a three-times-per-week,

supervised group setting exercise; a prescription for equivalent home-based, individual exercise;

sertralin; and a placebo pill. Initially researchers faced ethical concerns about assigning subjects

to a placebo treatment known to be less effective. However it is also known that depression is a

condition highly influenced by patient beliefs, and in a previous study where a placebo group

was not included the researchers results were met with skepticism. After sixteen weeks, 45% of

supervised exercise subjects, 40% of home-based exercise subjects, 47% of sertralin subjects,

and 31% of placebo subjects achieved remission. Again, the results suggest but cannot

definitively conclude that exercise is effective for treating depression. Also, as with

psychotherapy, effects of exercise treatments compared to medication were not significantly

different. The adjusted odds ratio of remission among the three active treatments compared with

placebo was 2.0, with a 95% confidence interval of .96 to 4.2. (Blumenthol et al., 2007). To




better understand the long-term effects of exercise as a potential depression treatment,

researchers followed-up six months after a different four-month study. The study, compared an

exercise treatment, a sertralin treatment, and a combined treatment. During the initial four

months depression improvements between groups were comparable, though at follow-up

continued exercise helped to prevent depression relapse. The odds of classification as depressed

at follow-up decreased 50% with every additional 50 minutes of exercise reported per week

(Babyak et al., 2000).

It also would be clinically useful to know the potential effectiveness of physical activity

as adjunct treatment. A study to examine exercise as an adjunct treatment to counselingcompared three groups: a running program, cognitive based counseling, and engagement with

both programs. Similar to previous studies comparing only running and counseling, all three

treatments reduced depression but were not significantly different from each other (Fremont J &

Craighead LW, 1987). Exercise has also been considered as an adjunct to pharmacological

treatment. In study with thirty female patients, a control group of twenty subjects receiving

pharmacological treatment was compared with ten subjects receiving physical activity training in

addition to the pharmacological treatment. Significantly improved depression measures were

found in the group treated with physical activity as an adjunct. Depression measures were

improved, but did not reach statistical significance in the control group (Pilu A et al., 2007).

These results suggest physical activity is a good candidate for use as adjunct depression

treatment, but studies with larger samples and greater control comparisons are needed to confirm

this conclusion.

Determinations of physical activity’s efficacy may vary upon whether experts consider

subthreshold depressive symptoms—those that do not reach a level for clinical diagnosis—to be




part of a spectrum of depressive disorders or distinct from clinical depression. Based on

Lewinsohn et al.’s analysis, depression can be conceptualized as a continuum, with no unique

consequence upon crossing the threshold of symptoms for clinical diagnosis of depression

(2000). Demonstrating this concept, as depression increased among adolescents the risk of a

substance use disorder within five years also increased, a relationship that held even among

subthreshold depressive symptoms. While no scientific consensus about subthreshold symptoms

currently exists, treatment of persistent subthreshold symptoms following a stepped-care model

of least costly and least aggressive treatments could be very beneficial for prevention of future,

more severe depression (Lewinsohn, Solomon, Seeley, & Zeiss, 2000).Physical activity could certainly serve as a free or little-cost prevention and treatment

strategy for people with subthreshold depressive symptoms and diagnosed depression. Greist et

al. calculate that running treatment compared to psychotherapy was four times more cost

effective in their clinic, where expenses totaled $115 for the running treatment compared to $500

for equally effective psychotherapy (1979). Physical activity is also minimally aggressive. It has

no known side effects when performed in a controlled manner and has also been shown

beneficial for improving cardiovascular disease, diabetes, and bone health (Chodzko-Zajko et al.,

2009). Factors such as motivation, social support and time commitments should be considered in

order to ensure the patient is able to follow through with exercise recommendations. Should

patients be unable to fully meet recommendations, clinicians would not want to provoke a sense

of failure that might exacerbate depression. With encouragement and realism from clinicians,

physical activity prescriptions could be an important intervention for improving mental health

(Donaghy & Taylor, 2010).




Future Research Directions

Depression in adolescents is currently understood primarily by applying results from

studies among adults. In fact, adolescent physiology and psychology is distinct in many ways.

More studies focusing specifically on adolescents, when first depression onset is greatest, could

provide a unique understanding of depression development and progression. Additional

adolescent studies would also provide a window to explore the protective effects of physical

activity by examining a time when depression risk dramatically increases (Kessler et al., 2003).

It may not be possible to prevent depression altogether but it is possible that long-term benefits

might result from delaying depression onset.Longer-term prospective-cohort studies and improved randomized control trials will add

validity and understanding to the field. Current studies are largely cross-sectional and cannot

assess temporality and causation. Prospective cohort studies would be particularly beneficial in

comparison to retrospective studies, which often involve difficulty distinguishing depression

first-onset from recurrences. Identification of first onset might help clarify both protective and

harmful risk factors (Kessler et al., 2003). Additionally, most trials are of short duration,

typically sixteen weeks or less. Yet depression is a long-term condition. The mean length of

depression in studies of children and adolescents is seven to nine months (Birmaher.et al., 1996).

Studies over greater periods of time will also add insight to potential relationships between

depression and physical activity.

Research that examines a joint effect of biology and environmental/social determinants is

also important. For example, the hypothalamic pituitary axis is an area of research where biology

and environment appear to be closely intertwined. Yet research that considers a joint effect from

biological and environmental determinants of physical activity and depression is still minimal.




Future risk factor research should more clearly appreciate both biological and environmental

contributions (Kessler et al., 2003).

Depression is a highly prevalent and debilitating illness. Depression typically emerges in

adolescence and is particularly prevalent among females. Meanwhile, physical activity could

potentially relate to physical activity through numerous mechanisms, including factors not yet

researched. Better understanding of the biological and environmental relationships between

depression and physical activity interactions could give rise to influential public health

interventions and improvements.




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