20 min a day to sanity!

December 6th, 2009  |  Published in Stumpblog  |  3 Comments

A large-scale observational study (nearly 20,000 people) shows that physical activity improves your chances of staying happy. The more you exercise, the better you feel.

At least 20 min/week of any physical activity (including domestic, walking or sports activities) meant a lower level of psychological distress. Participation in sports helped the most.

M Hamer, E Stamatakis, A Steptoe. Dose-response relationship between physical activity and mental health: the Scottish Health Survey Br J Sports Med 2009;43:1111-1114 doi:10.1136/bjsm.2008.046243

Objectives

Regular physical activity is thought to be associated with better mental health, although there is a lack of consensus regarding the optimal amount and type of activity to achieve these benefits. The association between mental health and physical activity behaviours was examined among a representative sample of men and women from the Scottish Health Surveys.

Methods

Self-reported physical activity was measured and the General Health Questionnaire (GHQ-12) was administered in order to obtain information on current mental health. Participants were 19201 men and women. Risk estimates per category of physical activity sessions per week were calculated using logistic regression models.

Results

Psychological distress (based on a score of 4 or more on the GHQ-12) was evident in 3200 participants. Any form of daily physical activity was associated with a lower risk of psychological distress after adjustment for age, gender, social economic group, marital status, body mass index, long-standing illness, smoking and survey year (OR 0.59, 95% CI 0.52 to 0.66, p<0.001). A dose-response relationship was apparent, with moderate reductions in psychological distress with less frequent activity (OR 0.67, 95% CI 0.61 to 0.75). Different types of activities including domestic (housework and gardening), walking and sports were all independently associated with lower odds of psychological distress, although the strongest effects were observed for sports (OR 0.67, 95% CI 0.54 to 0.82).

Conclusion

Mental health benefits were observed at a minimal level of at least 20 min/week of any physical activity, although a dose-response pattern was demonstrated with greater risk reduction for activity at a higher volume and/or intensity.

Discussion

The main findings from this study demonstrate strong associations between physical activity and reduced odds of psychological distress. The mental health benefits were observed at a minimum physical activity level of at least 20 min/week of any type of activity.

A dose-response pattern was also observed with greater risk reduction at higher activity levels, especially for sports. Our findings relating to the dose-response relationship between physical activity and mental health are largely consistent with reports from previous population studies, although it is difficult to make direct comparisons with our data because of the differences in measures of mental health and assessment of physical activity. For example, in the Harvard Alumni Study, men who expended 1000¨C2499 or ¡Ý2500 kcal/week were 17% and 28% less likely to develop clinically diagnosed depression compared with men who expended <1000 kcal/week.6 Australian women who performed 2¨C3 sessions per week or daily moderate intensity activity had approximately 20% and 40% reductions, respectively, in the risk of subclinical depressive symptoms after 5 years of follow-up.2

The mental health benefits of physical activity appear to be independent of potential confounding factors such as long-standing illness, obesity and smoking, although inclusion of these covariates reduced the strength of the association. Thus, the protective effects of physical activity may, in part, operate through these risk factors. Indeed, physical activity is associated with a reduced risk of chronic diseases such as CVD, diabetes, hypertension and some cancers.

Exercise is also thought to improve a number of biological risk factors such as dyslipidaemia, glucose intolerance, inflammation and vascular dysfunction, which have been related to mental health disorders such as depression and dementia. Given that heightened responsiveness to daily stressors is a risk factor for psychological morbidity, physical activity may also improve mental health by reducing biological stress reactivity.

What is already known on this topic

Mental illness such as depression is a risk factor for morbidity and mortality.

Regular physical activity is thought to be associated with better mental health.

The amount and type of activity that is required to achieve mental health benefits has not been clearly established.

This is the first study to our knowledge that has specifically considered the importance of different activity types in relation to mental health. Stamatakis et al recently reported that, in contrast to leisure time activities, domestic activity was not associated with improvements in CVD risk factors which may partly explain why domestic activity contributed less to mental health benefits in the present analyses. Indeed, previous work has also shown a graded dose-response relationship between cardiorespiratory fitness and depressive symptoms, suggesting that participation in vigorous sports activities that produce greater fitness improvements is most beneficial for mental health.

It is, however, possible that the additional benefits gained from participating in sports may have a psychological component, such as fostering social support networks and developing mastery and better coping abilities. In addition, the measurement of domestic activity may be less reliable than for other forms of activity, increasing error variance.

What this study adds

Lower levels of psychological distress were observed at a minimal level of at least 20 min/week of any physical activity (including domestic, walking or sports activities).

A dose-response pattern was demonstrated with greater risk reduction for activity at a higher volume and/or intensity.

The limitations of the present study should be recognised. Given the cross-sectional nature of this study, we cannot exclude the possibility that the present results are explained by reverse causality or confounding from unmeasured variables. In particular, co-morbidities that cause functional impairment may have influenced the results because the association between depression and physical disability may be bidirectional.

However, we attempted to control for long-standing illness in our analyses and we found a strong inverse association between physical activity and psychological distress in participants with existing CVD, suggesting that these associations are not secondary to co-morbidity. Causality, however, remains an issue. Using a co-twin control method, Stubbe et al recently suggested that the association between exercise participation and higher levels of life satisfaction and happiness was non-causal and mediated by genetic factors that influence both exercise behaviour and well-being. However, further genetic studies are required to confirm these findings.

In the present study we did not separately assess the association between physical activity and positive well-being, which appears to be an independent risk factor for health. A strength of the study is the large sample size of both men and women and the availability of detailed physical activity information covering both recreational and lifestyle (eg, walking, domestic) activity. Further studies should attempt to examine the effects of exercise intensity on mental health using objective measures.

In summary, mental health benefits were observed at a minimal level of at least 20 min/week of any physical activity, although a dose-response pattern was demonstrated with greater risk reduction for activity at a higher volume and/or intensity.

Responses

  1. Teneshia says:

    December 11th, 2009at 12:25 am(#)

    Thanks for this post.

    When I started grad school, going to the gym became my new obsession. Over the months I’ve found myself to be a helluva lot less anxious, depressed and stressed than I was when I was an undergrad. It’s amazing what a little sweat can do. It’s nearly magical…

  2. Elizabeth says:

    January 7th, 2010at 10:50 pm(#)

    I cannot agree with this sentiment enough. Funnily I too started regular exercise in grad school as well, when I don’t exercise I’m angrier, more depressed and I can’t sleep properly at night.

    P.S. Thank you for all your amazing articles. I’m now onto free weights at the gym instead of machines. I’m getting a lot better results this way.

  3. Blog-watch: exercise for mental health and brain development says:

    January 28th, 2010at 3:54 pm(#)

    [...] A good starting point to mental prowess is to start with good mental health and that is helped by happiness.  Krista at Stumptuous reported on an observational study that showed that physical exercise reduced psychological distress. [...]


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