A recent study on exercise and the prevention of depression aimed to determine whether or not exercise provides protection against new-onset depression, the intensity and amount of exercise required to gain protection, and how the protection might work.
To do this they examined 33,908 adults, selected on the basis of having no symptoms of the common mental disorder or limiting physical health conditions. The researchers followed them for 11 years, during those years they collected measures of exercise, depression, anxiety, along with a range of potential confounding and mediating factors.
What they concluded was that regular exercise of any intensity does indeed provide protection against future depression. Even relatively modest changes in levels of exercise may have important public mental health benefits and prevent a surprisingly high number of new cases of depression.
The study suggests that 12% of future cases of depression could have been prevented if the participants had engaged in at least one hour of physical activity each week. Interestingly, the majority of the protective effects occurred at low levels of exertion and were observed regardless of intensity.
The HUNT Study
Another study (the HUNT study) followed thousands of participants in Norway for 9-13 years. They found their volunteers by inviting the entire population, aged 20 or older, to fill out a basic screening form for depression and anxiety. After reviewing the submissions, they invited the happiest 70% to participate. 8,400 were excluded due to serious physical illness, which left nearly 34,000 in the study.
Potentially confounding data, such as smoking status, BMI, resting heart rate, and demographic data were collected at various visits over the years. Blood pressure, heart rate, weight, height, waist, and hip circumference were measured by specially-trained nurses. The research team also accounted for variables which might impact the association between exercise and common mental illness. These included socio-economic and demographic factors, substance use, new onset physical illness, and perceived social support. In the end, about 22,500 participants completed the study.
At the beginning of the HUNT study, all participants were asked to report their frequency of weekly exercise and their degree of aerobic intensity using three different categories:
- Without becoming breathless or sweating
- Becoming breathless and sweating
- Exhausting themselves
During the follow-up stage of the study, participants completed a self-report questionnaire (using the Hospital Anxiety and Depression Scale) to indicate whether the subject was experiencing any anxiety or depression during the years of the study.
Correlation Between Exercise and Depression
In a nutshell, those participants who exercised were less likely to develop depression than those who didn’t. The cool thing is, it didn’t matter how much exercise they did as long as they did some kind of “deliberate physical activity” for a minimum of an hour per week.
Yup, only one hour of exercise for the entire week and it also did not matter how intense that exercise was. It could be a leisurely bike ride, CrossFit, spin class or yoga. We’ll get into some other creative options in a bit.
Research author Samuel Harvey from Black Dog Institute and UNSW stated: "We've known for some time that exercise has a role to play in treating symptoms of depression, but this is the first time we have been able to quantify the preventative potential of physical activity in terms of reducing future levels of depression. These findings are exciting because they show that even relatively small amounts of exercise—from one hour per week—can deliver significant protection against depression.”
That's good news for all of us who just can't or don’t want to commit to a daily and lengthy gym session or can’t even imagine signing up to run a marathon.
Staying on an Exercise Routine
The social and physical health benefits of exercise partially explain the shielding of depression, but the research also reported that some biological mechanisms, like alterations in the vagal tone, did not appear to have a role in protecting against depression.
If the social benefits of exercise make the real impact, it would appear that simply getting out and about, getting your heart rate up, and engaging in some active self-care is what makes the real difference. Although the researchers felt that a lot still remains unexplained.
There is also a question of whether there's actually a "reverse causation" going on—people with mental health issues may struggle to get enough exercise in the first place. So it can be a chicken-and-egg scenario: which comes first, the lack of exercise or the depression?
The thought here is that if we are sick, or blue, or overwhelmed, it is our lunchtime workout or our morning jog that is the first thing to get taken off of the to-do list. But the data suggests that if we maintain even a brief schedule of light activity, we lower the chances of developing depression in the future. Preventing 12% of depression cases is significant, and you don’t even have to step foot in a gym to make it happen.
These results drive home the need to integrate exercise into mental health plans and into broader public health campaigns. If we can find ways to increase the population's level of physical activity, even by a small amount, we will likely see substantial physical and mental health benefits across the board.
With sedentary lifestyles becoming the norm worldwide, and rates of depression being on the rise, these results are of particular importance because they highlight that, once again, even a small lifestyle change can lead to significant mental health benefits.
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