Physical activity – especially vigorous aerobic exercise – has been shown to alleviate depression. Might it also reduce the risk of suicide, which is linked with depression? This is the hypothesis a pair of US scientists set out to test with a major questionnaire survey of nearly 5,000 college students, for whom suicide is the third leading cause of death.

Students were classified according to whether or not they participated in any college sport teams. They were further grouped into five categories relating to their level of activity in the week preceding the survey, as follows:

Frequent vigorous activity – exercise that made them sweat and breathe hard for 20 minutes or more on six or seven days;
Vigorous activity – as above for three-five days;
Moderate activity – a combined total of one or two days of vigorous activity and five or more days of walking or cycling for 30 minutes a day;
Low activity – some activity but less than amounts typically recommended for health and fitness gains;
No activity – the ‘control’ condition.
Students were characterised as suicidal if they indicated that during the past 12 months they had seriously thought about attempting suicide, made plans about how they would attempt suicide or actually attempted suicide.

The results revealed distinct – and puzzling - gender differences in the association between activity and suicide, although the actual prevalence of suicidal behaviour among male and female students was similar.

In terms of sports participation, there was a trend in favour of a protective effect, with male non-participants being 2.5 times more likely to report suicidal behaviour than participants and female non-participants 1.67 times more at risk – the latter finding being only of borderline statistical significance.

But when it came to activity levels the differences were more stark. For men, low activity was the only clearly protective level, with participants at almost half the risk of suicidal behaviour of those with no reported activity; the men in the three more active groups did not differ significantly in reported suicidal behaviour from the controls.

Women, however, exhibited a completely different risk profile, with those reporting frequent vigorous activity having twice the risk of suicidal behaviour of the control group and moderately active women being 1.76 times more at risk. Women in the other two activity groups had slightly – but non-significantly – higher odds of suicidal behaviour than the controls.

These very different findings caused the researchers to engage in a great deal of head-scratching, having hypothesised at the outset that sedentary students of both sexes would run the highest risk of suicidal tendencies. They were especially puzzled by the finding (derived from further analysis of the data) that the association between physical activity and suicidal behaviour in women was independent of distorted weight perceptions that might drive them to exercise obsessively.

‘Our findings suggest,’ they conclude, ‘that collegiate women who are at risk for suicidal behaviour may be using exercise to cope with distress or stressors, independent of concerns about being overweight. Future research should attempt to identify other factors that may be mediating an association between physical activity and suicidal tendencies among college-age women.’

Meantime, they suggest that health professionals are in the best position to recommend increased physical activity when appropriate and to determine when such activity is being used excessively or inappropriately in order to mask problems that may require intervention.

Med Sci Sports Exerc 2002 Jul;34(7):1087-96.