Physical activity not only helps prevent depression, but should be considered an effective therapeutic option for patients who already have the condition, researchers say.
According to a review published recently in Current Sports Medicine Reports, major depressive disorder is an exceedingly common, disabling condition with prevalence estimates ranging from 6% to 18% across different countries worldwide.
At present, the mainstays of treatment are antidepressants and psychotherapies. But neither of these options are ideal. While both are better than placebo, they have relatively poor rates of effectiveness and are also associated with high dropout rates, poor adherence and, in the case of medication, can be associated with side-effects.
It is little wonder then that people are looking to alternatives, especially factors they can modify themselves to help protect against this mental illness, say the two experts from the UK and Brazil.
“There is growing recognition that lifestyle behaviours, such as physical activity and exercise partially contribute to the risk of developing depression and can be useful strategies for treating depression, reducing depressive symptoms, improving quality of life, and improving physical health outcomes,” they wrote.
To start with, there’s a wealth of evidence to support the protective role of physical activity against depression. Among other studies, the researchers cite a US cross-sectional study that found people who engaged in regular vigorous exercise were more than three times less likely to experience depression than people who only undertook light physical activity.
Of course, these types of observational studies can’t always determine cause and effect, but when the researchers investigated just those prospective studies, including people free from depression at baseline, they found physical activity reduced the risk of depression by 17%.
As for using exercise as a treatment for depression, there has been a lot of research done proving its benefit, but as to how much is less clear. The magnitude of this positive effect seems to vary enormously. This is partly because it is difficult to quantify exercise in terms of intensity. For instance, one study might include walking as exercise compared with sedentary lifestyle whereas another might look at high energy aerobics.
“Comparing ‘exercise versus exercise’ is a significant limitation of the analysis since exercise, even when it is of lower intensity, exhibits a significant reduction in depressive symptoms,” they wrote.
So should we be recommending increasing physical activity for everyone with depression? The reality is, exercise won’t work for everyone.
According to what the researchers call a seminal study, physical activity had a 40% response rate for depression. While that’s not bad, the real question is can we pick which patient will respond and which one won’t?
There are some biomarkers that are reasonable predictors of a positive response, such as higher levels of brain derived neurotrophic factor(BDNF) and tumour necrosis factor-alpha. Interesting, but ultimately not that helpful in general practice.
Of more practical use is the evidence that suggests better global functioning is associated with a better chance of response. In addition, studies show men, regardless of family history of mental illness, and women without a family history, are more likely to benefit from exercise.
Also of importance is the finding that social support can be critical, not only to the effectiveness of exercise as a therapy but also to maintenance of this therapy and its response.
“The supervision of exercise professionals can increase the chance of adherence and success to the treatment,” the researchers concluded.
Current Sports Medicine Reports; 8 Aug 2019