"Available evidence supports the notion that physical activity can confer protection against the emergence of depression regardless of age and geographical region."
So said the findings reported by Felipe Schuch and colleagues  who undertook a review of the existing peer-reviewed research literature looking at whether physical activity a.k.a exercise *might* provide some important protection against the development of depression. Such a review took place in the context that NHS Choices, the go-to place for health and medical information here in Blighty, already has an entry called 'exercise for depression'.
The authors - many of whom are quite recognisable names in the area of science looking at the physical and the mental coexisting together - located almost 50 studies labelled as prospective cohort studies including over a quarter of a million participants residing across the globe. They undertook a meta-analysis - combining all the data from the various studies together and coming up with a sort of consensus finding - and concluded that yes, physical activity does seem to have a positive effect on reducing the risk of depression. The level of the decrease in risk of depression from participation in physical activity seemed to vary slightly according to age, amount of exercise and geographical region, but the trend was most definitely in the protective direction across such variables and remained even after potentially important variables such as body mass index (BMI) and tobacco smoking were taken into account. The authors also reported that: "Although significant publication bias was found, adjusting for this did not change the magnitude of the associations" indicating that although there was a tendency for results 'friendly' to the 'physical activity might reduce depression' hypothesis to be published over less positive results, this did not seemingly affect the findings in any particularly meaningful way.
Accepting that there is a further scheme of work required on this topic in terms of things like what physical activities might be 'best' for depression or depressive symptoms (see here), how to measure physical activity more objectively (ahem, actigraphy) and what the mechanism(s) of effect might be, these are important results. I can think of many, many different areas that the Schuch results could be pertinent to; several already covered on this blog (see here and see here). Many of those areas / conditions / labels reflect states where either physical activity seems to be reduced by choice (see here) or through necessity (see here) but the net result could be the same in terms of elevated risk of depression.
Still, the general message emerging from the Schuch paper is: if you can, move more, and perhaps not just for the physical benefits that accompany physical activity.
And just in case you need some more reading material on this topic, you could do a lot worse than the paper by Brett Gordon and colleagues  who concluded that: "Resistance exercise training significantly reduced depressive symptoms among adults regardless of health status, total prescribed volume of RET, or significant improvements in strength."
 Schuch FB. et al. Physical Activity and Incident Depression: A Meta-Analysis of Prospective Cohort Studies. Am J Psychiatry. 2018 Apr 25:appiajp201817111194.
 Gordon BR. et al. Association of Efficacy of Resistance Exercise Training With Depressive Symptoms. JAMA Psychiatry. 2018. May 9.