If healthy adults exercise for a minimum of an hour each week, their risk of incident depression can be reduced by 12%, a Norwegian prospective cohort study has found.

Data were obtained from the HUNT study which has followed a large Norwegian population since 1984. Those with symptoms of common mental disorder (identified with the 12-item Anxiety and Depression Symptom Index) and those reporting psychological impairments were excluded from the study. Those reporting physical illness or disability were also excluded. A total of 33,908 ‘healthy’ adults were selected from the baseline participants.

Participants were followed up for 9-13 years. At the baseline assessment they were asked to complete an exercise questionnaire which included questions on frequency, duration and intensity. At follow-up, they were asked to complete the Hospital Anxiety and Depression Scale (HADS). Caseness was defined using a cut-off score ≥ 8 in both the anxiety and depression subscales.¹

Compared with those who exercised for 1-2 hours a week, those who undertook no leisure time exercise were significantly more likely to have elevated depressive symptoms at follow-up; adjusted odds ratio 1.44 (95% CI: 1.17-1.78).

There was no evidence that exercising for more than one hour a week or increasing the intensity of exercise conferred any additional benefit.

There was no correlation between regular exercise and incident anxiety symptoms.

The population attributable fraction, i.e. the proportion of depression cases that could be attributed to failure to exercise for at least one hour a week, was 12%.

A Scottish cross-sectional study also found that very modest levels of physical activity (> 20 minutes/week) were associated with a reduced likelihood of psychological distress (GHQ-12 ≥ 4).  However, the results differed from the present study in that a greater risk reduction was found with a higher volume of exercise and more intense activity.²

The present study is superior to the Scottish study both in terms of the number of participants (33,908 vs 3,200) and the longitudinal design (which reduces the possibility of reverse causation). However, the authors caution that misclassification may have affected the results.

Both exercise levels and depression and anxiety were classified using self-report measures.

The present study provides a further reason for GPs to recommend regular exercise to all their patients providing there are no medical contraindications.

There is a need for further studies to investigate the potential value of exercise in depression relapse prevention i.e. secondary prevention.

Dr Phillip Bland

Harvey SB, Øverland S, Hatch SL et al. Exercise and the prevention of depression: results of the HUNT cohort study. Am J Psychiatry 2017;doi:10.1176/appi.ajp.2017.16111223