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Lower Fitness Levels Could Exacerbate Depression, Study Finds

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Key Takeaways

  • There is much evidence in support of a link between regular exercise and good mental health.
  • Recently, researchers found that people with low aerobic and muscular fitness are almost twice as likely to experience depression than their fitter counterparts.
  • The study also found a 60% higher risk of anxiety in people with low fitness levels.

A study led by researchers at University College London, published in BMC Medicine, found that people with low aerobic and muscular fitness are almost twice as likely to experience depression. The authors also predicted a 60% higher risk of anxiety.????

This came as no surprise to board-certified cytopathologist Celina Nadelman, MD. "Physical activity improves cognitive functions; it improves attention, cognitive control of behavior, academic performance, memory, and information processing speeds," she says. "It also increases problem-solving and improves decision making and cognitive flexibility, such as multitasking. In addition, physical activity has short- and long-term effects on mood and emotion, promising a positive effect and inhibiting a negative one."

And when we don't exercise, we start to lose all those benefits. "The healthy blood flow to our brain decreases," Dr. Nadelman says. "Our cognition and executive functioning skills may become muddied, our brain becomes not as resilient to disease, we become more stressed, and our overall quality of life decreases. This process of losing brain function due to a lack of physical activity begins to happen in as little as 10 days without healthy movement."

These findings could help inform individuals and mental health professionals when discussing non-pharmacological options for depression prevention and management.

Study Findings

A total of 152,978 people, age 40 through 69, took part in the U.K. Biobank study.?? At the beginning of the study, they were all tested on their aerobic fitness (using a stationary bike with increasing resistance) and their muscular fitness (via a grip strength test). They also answered a questionnaire to determine whether they had any symptoms of anxiety or depression.

Celina Nadelman, MD

Physical activity has short- and long-term effects on mood and emotion, promising a positive affect and inhibiting a negative one.

— Celina Nadelman, MD

After seven years, the same people were tested for anxiety and depression symptoms. The researchers discovered that those who had high aerobic and muscular fitness at the start of the study reported better mental health at the time of follow-up.?

Compared to participants with high levels of fitness, people with the lowest combined aerobic and muscular fitness were 98% more likely to have symptoms of depression, 60% more likely to have anxiety, and 81% more likely to have either anxiety or depression.?

What Makes This Study Different?

There's no shortage of studies finding that people who exercise more are less likely to experience mental illness, but much of the research relies on participants self-reporting their activity levels via questionnaires. This isn't always the most reliable measure. The UCL study, on the other hand, used objective measures, namely exercise and fitness tests.

"We also looked at these relationships over time, which means we could adjust our analysis for mental health at the start of the study and reduce the risk of reverse causation, i.e. poorer mental health causing low fitness," explains the study’s lead author, PhD student Aaron Kandola.

The researchers accounted for other factors at baseline that could interfere with the results, like diet, socioeconomic status, and chronic illness. "We also had a very large sample size, which helps to increase the statistical power of our results," Kandola adds.

Celina Nadelman, MD

Aerobic exercise lowers certain cellular reactivity and thus reduces biological response to stress (e.g. a reduction in cortisol and lower heart rate).

— Celina Nadelman, MD

Kandola says the most surprising aspect of their findings was the magnitude of the associations between fitness levels and mental health. For context, a recent systematic review of 49 studies found that low physical activity was associated with 17% higher odds of depression.?? Meanwhile, the UCL study linked low aerobic and muscular fitness to 98% higher odds of depression. "While these aren’t directly comparable for several methodological reasons," Kandola explains, "the difference is much larger than we expected.”

How Does Exercise Improve Mental Health, Exactly?

According to Dr. Nadelman, one way physical activity bestows these benefits is through decreasing the biological response to psychological stress. "The stress hormone, cortisol, is released when a person is stressed (as in the 'fight or flight reaction')," she explains. "This is an adaptive biological outcome that may not be as useful as it was during cavemen days!"

Dr. Nadelman explains that modern day stressors are usually not fleeting and increase cortisol in a continuous manner. "This increase in cortisol has neurotoxic effects on the brain which can damage, for example, the hippocampus, and lead to depression," she says. "Aerobic exercise lowers certain cellular reactivity and thus reduces biological response to stress (e.g. a reduction in cortisol and lower heart rate)."

Aaron Kandola

People with low fitness should start slow, keep the exercises simple, build up over time, and not rush into intense aerobic or resistance training regimes.

— Aaron Kandola

And then there's the so-called "runner's high," caused by continuous exercise. "This is through the release of endogenous chemicals, or euphoriants such as endorphins," Dr. Nadelman says.

“People with low fitness should start slow, keep the exercises simple, build up over time, and not rush into intense aerobic or resistance training regimes,” says Kandola. He suggests trying to combine different activities into a routine to keep multiple aspects of fitness at a good level (i.e. resistance and cardio exercises to keep muscular and aerobic fitness levels up).?

Even just 30 minutes a day of physical activity improves thinking skills, information processing, brain cell growth and resilience, stress management, memory, academic performance, and can help prevent or manage mental illness and neurodegenerative disorders, Dr. Nadelman adds. So you don't have to hit the gym for hours at a time or start training for a marathon—unless you want to, of course.

What This Means For You

The health benefits of keeping fit are undeniable. But if you're not in a regular exercise regimen, don't worry, and don't push yourself too hard.

And if you struggle to reach 30 minutes of exercise per day, Dr. Nadelman suggests starting with five minutes and adding an additional five minutes each day or each week until reaching 30 minutes. You could also hire a trainer or ask a friend or loved one to exercise with you or to hold you accountable.

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  1. Kandola A, Osborn DP, Stubbs B, Choi K, Hayes JF. Individual and combined associations between cardiorespiratory fitness and grip strength with common mental disorders: a prospective cohort study in the UK Biobank. BMC Med. 2020;18:303. doi:10.1186/s12916-020-01782-9

  2. Schuch FA, Vancampfort D, Firth J, et al. Physical activity and incident depression: a meta-analysis of prospective cohort studies. Am J Psychiatry. 2018;175(7):631-48. doi:10.1176/appi.ajp.2018.17111194