An hour a week of low-intensity exercise may be all it takes to prevent depression, a large, population-based cohort study of healthy adults suggests.

"Being active is good for you ― even in small doses. Taken regularly, exercise is good for you, and it probably prevents mental ill health," senior author Matthew Hotopf, PhD, director of the South London and Maudsley NHS Foundation Trust National Institute of Health Research Biomedical Research Center at Kings College London, the United Kingdom, told Medscape Medical News.

"So if physicians have a patient with a history of depression, this advice is probably particularly important: do regular, small amounts of enjoyable exercise. Patients don't have to run a marathon," Dr Hotopf added.

The study was published online October 3 in the American Journal of Psychiatry.

No Added Benefit Beyond 1 Hour

The HUNT (Health Study of Nord-Trøndelag County) study is among the largest and most comprehensive population-based health surveys ever done.

Phase 1 of the study was carried out between January 1984 and February 1986. All persons aged 20 years and older living in Norway's Nord-Trøndelag County were invited to respond to questions about their lifestyle and medical history. They also underwent a physical examination.

A total of 74,599 persons responded to the survey. All participants were followed for a period of 9 to 13 years during phase 2 of the study.

"At the time of their baseline assessment (HUNT 1), all participants were asked how often they engaged in exercise (such as walking or swimming)," the investigators write.

The researchers graded the intensity of the exercise on the basis of answers to questions as to whether the participants exercised without becoming breathless or sweating; whether exercise resulted in breathlessness and sweating; or whether exercise resulted in near exhaustion.

A total of 22,564 individuals were successfully assessed during phase 2 of the HUNT study. The authors stressed that this was a very healthy cohort of individuals at study outset. Younger participants and women were significantly more likely to be undergo follow-up assessment.

"After adjustment for a range of confounders, those who reported undertaking no exercise at baseline had a 44%...increased odds of developing case-level depression compared with those who were exercising 1-2 hours a week," the investigators report.

The authors also found a significant negative relationship between the total amount of exercise undertaken at baseline and risk for future depression (P = .001).

They also determined that had everyone exercised at least 1 hour a week, 12% of the cases of depression that were identified at follow-up could have been prevented.

The same was not true for anxiety, the prevalence of which was similar at follow-up regardless of the level of baseline exercise.

Dr Hotopf and colleagues also found a significant protective association between baseline levels of exercise and future depression for those younger than 50 years (P = .04) and for those older than 50 years ( P = .03).

"Most of the protective effect of exercise is realized with relatively low levels of exercise, with no indication of any additional benefit beyond 1 hour of exercise each week," the investigators note.

"The protective effect was seen equally across all groups, regardless of the intensity of exercise that was undertaken or the gender or age of the participants," they add.

"The results of this study indicate that relatively modest increases in the overall amount of time spent exercising per week may be able to prevent a substantial number of new cases of depression," they conclude.

Confirmatory Findings

Commenting on the findings for Medscape Medical News, Mats Hallgren, PhD, a researcher at the Karolinska Institute in Stockholm, Sweden, said a study he conducted into the treatment of mild to moderate depression yielded similar findings.

ThAT study involved 946 patients with mild to moderate depression who were assigned to undergo either yoga or stretching, moderate aerobic exercise, or vigorous aerobic experience. Patients were encouraged to participate in three exercise sessions a week, but most only attended about one per week, Dr Hallgren pointed out.

At the end of 12 weeks, Dr Hallgren and colleagues found that the severity of depression was significantly lower among patients who participated in any one of the exercise interventions compared to those who received usual care, and that the benefits of exercise were seen regardless of how intensely the patients exercised.

Furthermore, the benefits of exercise on depression were maintained 12 months after baseline assessment, despite suboptimal adherence.

"I think the recommendation should not be to exercise only once a week, because people need to exercise more than once a week for general health, so for that reason alone, we should recommend that people exercise three times a week," Dr Hallgren said.

"But even if they exercise only once a week, exercise can still have beneficial effects on depression," he added.

"Exercise is medicine for depression, even when the 'pill' is small," Dr Hallgren affirmed.

The authors and Dr Hallgren have disclosed no relevant financial relationships.

Am J Psychiatry. Published online October 3, 2017. Abstract

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