Physical Activity

Cross-sectional studies have consistently associated high self-reported levels of habitual physical activity with better mental health and a correlation of habitual exercise level with low depression (but not anxiety) has been described in adolescents (Morris et al. 1992) and elderly subjects (Ruuskanen and Ruoppila 1995). Controlling for social class and health status, Steptoe and Butler (1996) showed in a large cohort (n = 5,061) that vigorous exercise par-ticipation was related to lower emotional distress. In line, Steptoe et al. (1997) reported that after controlling for age and sex, exercise correlated with lower depression in 16,483 undergraduates. In upper Bavaria, Germany (n = 1,536) (Weyerer 1992) and in separate samples from the United States and Canada totaling 55,000 subjects (Stephens 1988), self-reported level of recreational physi-cal activity correlated with better mental health, including fewer symptoms of both anxiety and depression (after controlling for confounding variables including age, sex, sociodemographic status and physical illness). In the European Union, physical activity (in everyday life) as measured with the IPAQ was associated with self-rated health in general (Abu-Omar et al. 2004b) and also with self-rated mental health (Abu-Omar et al. 2004a). A total of 16,230 respondents, age 15 years and above, were studied; in some of the 15 nations, evidence for a dose-response relationship between physical activity and mental health was found. On a diagnostic level, Goodwin (2003) ana-lyzed the data of the US National Comorbidity Survey (n = 5,877): the association of regular physical activity and lower prevalence of current major depression, social phobia, specific phobia, and agoraphobia was significant and persisted after controlling for sociodemographic char-acteristics, self-reported physical disorders and comorbid mental disorders. In most studies, fitness was not directly assessed and Thirlaway and Benton (1992) found that fitness interacted with exercise habits such that highly fit subjects who do not exercise had poorer mental health status than all others; fit nonexercisers may have been temporarily prevented from exercising, which may worsen the mood and increase anxiety (Morris et al. 1990). Simultaneously, measuring exercise habits and mood or anxiety (disorders) in cross-sectional survey is inherently ambiguous about cause and effect. Therefore, prospective longitudinal studies are necessary to further characterize the association of physical activity and mental disorders. Until now, these studies are rare and at least in part, prospective longitudinal studies support results and hypothesis derived from cross-sectional studies: Paffen-barger et al. (1994) found that physical activity negatively correlated with depression approximately 25 years later in a sample of 10,201 men. In a sample of 4,848 subjects, Camacho et al. (1991) reported that the absence of exercise habits was linked to later depression across two 9-year periods. However, this study did not control for depression at study entry. In 2,084 elderly people, strati-fied into low and high depression, daily walking predicted improved depression in both the groups after 3 years (Mobily et al. 1996). In older adults, Strawbridge et al. (2002) reported a protective effect of physical activity on the development of depression. Studying 1,900 subjects for 8 years, Farmer et al. (1988) reported that regular exercise reduced the risk to develop a depression. In line, Motl et al. (2004) reported that naturally occurring changes in physical activity are inversely related to depressive symptoms during early adolescence. In a sample of 2,548 adolescents and young adults, we recently described that subjects with regular physical activity had substantially lower overall incidence of any and comorbid mental disorders after 4 years and a lower incidence of somatoform-, dysthymic- and some anxiety disorders (Stro¨hle et al. 2007).