Scientists have found some concrete evidence that exercising a little bit every day does reduce depression symptoms and boost overall mood.
For years, studies have found a connection between working out and lower depression risk – we all know exercise releases endorphins and endorphins make you happy.
But until now, there was no evidence to show a causal relationship when it came to depression – whether physical activity really did affect the condition, or simply that people with depression exercised less.
Now, a study by researchers at Massachusetts General Hospital (MGH) has presented evidence based on genetic data showing that working out is beneficial – and found no evidence that depression affects your ability to work out.
The team says the findings could help doctors and officials to develop prevention strategies for the growing number of people battling symptoms of depression.
For years, studies found a connection between working out and lower depression risk. But there was no evidence to show a causal relationship. Now researchers at MGH have found evidence for it
‘On average, doing more physical activity appears to protect against developing depression,’ says Karmel Choi, PhD, of the Psychiatric and Neurodevelopmental Genetics Unit in the MGH Center for Genomic Medicine, lead author of the report.
‘Any activity appears to be better than none; our rough calculations suggest that replacing sitting with 15 minutes of a heart-pumping activity like running, or with an hour of moderately vigorous activity, is enough to produce the average increase in accelerometer data that was linked to a lower depression risk.’
WHY RESEARCHERS HAVE STRUGGLED TO CONNECT THE DOTS – BUT GENES COULD OFFER AN ANSWER
Epidemiology is the study of what causes health outcomes and disease, and how to control them.
But very often the things we’re trying to understand – why some people love to drink alcohol, what causes anxiety, who is at higher risk for certain cancers – are hard to measure clearly.
Most studies end up being observational. In other words, scientists track their variables – in this case, physical activity levels and depression diagnoses – to see if the theory matches up.
However, that is very rarely enough to determine a causal relationship. Even if you try to account for all the variables again and again, there will still be a gap in your data.
In a bid to dig deeper, and to eliminate one of the biggest question marks, the MGH team employed a popular technique: using genes as a framework.
Both depression and physical activity can be affected by our genes. Some people are more naturally athletic, some are more prone to depression.
Using genomic data, we can stabilize that factor. We can determine whether people with depression are simply just less active, or not.
The technique (known as Mendelian randomization) is not a silver bullet; you are still left with room for other explanations. But it gets us as close as possible to confirming a cause.
HOW THEY DID IT
They pooled data from the UK Biobank and a global research group.
For physical activity, they had two pools of results: one in which 377,000 people reported their own physical activity, and another in which 91,000 people wore fitness trackers to monitor their movement. This was compared to genetic tests.
For depression, they analyzed the genetic makeup of 143,000 who were diagnosed with depression.
The results of the Mendelian randomization study found no connection between self-reported activity and lower rates of depression.
But when they looked at data from the fitness trackers, they did see improvement: those who worked out regularly had fewer symptoms of depression.
The researchers said there is a myriad of easy explanations for that gap. Firstly, our memories are not always perfectly accurate, and sometimes we are driven to slightly curate our own version of what happened. Secondly, and crucially, many may not count everyday movement, such as climbing the stairs or walking to the subway, as exercise, whereas a fitness tracker would.
They found nothing to suggest depression could hamper physical activity, nor that people with depression were less physically capable.
Senior author Jordan Smoller, MD, ScD, director of the Psychiatric and Neurodevelopmental Genetics Unit and a professor of Psychiatry at Harvard Medical School, says that gene variants do not determine a person’s behaviors or outcomes.
However, he says: ‘[T]heir average associations with certain traits in these very large studies can help us look at a question such as whether physical activity – or the tendency to engage in more physical activity – has a likely causal effect on depression.
‘And the answers to those questions could help researchers design large-scale clinical trials.’
Choi adds: ‘And of course it’s one thing to know that physical activity could be beneficial for preventing depression; it’s another to actually get people to be physically active.
‘More work needs to be done to figure out how best to tailor recommendations to different kinds of people with different risk profiles.
‘We currently are looking at whether and how much physical activity can benefit different at-risk groups, such as people who are genetically vulnerable to depression or those going through stressful situations and hope to develop a better understanding of physical activity to promote resilience to depression.’