The secret to why exercise is so good for mental health? ‘molecule of hope’

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Exercise, in whatever form, and for whatever duration, but life feels better. I feel it myself after a walk up Arthur’s Seat here in Edinburgh, a jog around the Meadows, or a sweaty hot yoga session in Leith. The physical benefits of movement, such as lowered blood pressure, reduced risk of diabetes and cancer, and healthy ageing, are well known, and we are beginning to understand more about the mental health benefits as well.

One of the most interesting health research projects of the last decade or so has looked at how exactly exercise makes us feel good. Research shows that there appears to be a clear scientific reason, that we can see at a cellular level. When muscles contract, they release chemicals into the bloodstream. Among these chemicals are myocins, which have been called “molecules of hope”. These small proteins go to the brain, cross the blood-brain barrier, and act as antidepressants. They do this by improving our mood, our ability to learn, our capacity for locomotor activity, and they protect the brain from the negative effects of aging. This is referred to as “muscle-brain cross talk”.

They are also responsible for improved metabolism, reduced inflammation, and increased muscle strength. Myokines are not only responsible for feeling good: exercise also releases neurotransmitters such as dopamine, noradrenaline and serotonin which have a positive effect on our brains.

Related: The five-minute fix: how to improve your fitness, strength and posture at super-fast speed

The nitty gritty of myokines and basic cellular mechanisms are complex. But the basics are not rocket science. Our brains and bodies get better with exercise and physical activity, and with more exercise we feel less anxious and depressed. It is a case of laboratory and experimental science that gives us insight into the phenomenon we recognize from our own lives, and from the many public health studies that show the benefits of exercise.

The largest synthesis study on the effect of exercise on major depressive disorder and depressive symptoms showed moderate to large effects of exercise on depressive symptoms. The authors argue that exercise is an effective treatment option for those who suffer. This has led to “social prescriptions” from GPs such as more time outdoors, daily walks, and a move from a purely medical model of care to a model of care that best suits the individual, mixing physical activity, community involvement and medicine when necessary.

The links between physical activity and mental health are particularly strong for children and young people too. A large study from Norway showed that teenagers who were physically active in teen sports had higher self-esteem and life satisfaction, especially for senior high school girls. This was also true for university students where a clear association was found between inactivity and poor mental health, self-harm and suicide attempts.

But trends are going in the wrong direction. Young people are spending more time on devices, and less participating in sport and other physical activities. This has significant consequences for mental health: a study of 40,000 children in the US found that after more than an hour a day of use, screen time was associated with less curiosity, lower self-control, less emotional stability and lower psychological well-being. Among children aged 14 to 17, those who used screens during the day were twice as likely to be diagnosed with depression. With the stresses of adolescence – be it peer pressure, post-Covid-19 trauma, exams, isolation and an uncertain economic future – sport, especially team sport, is a good protective measure for mental health. But the links between mental health and sport are rarely part of conversations about “mentally healthy school environments”, sport in the education curriculum, or raising resilient young people.

We could do much more to foster a healthy, lifelong relationship with exercise. It is a sure way to improve people’s health by preventing illness, rather than waiting until someone is already ill. And it’s not just about maintaining a certain weight or being a certain size: it’s about our bodies functioning and being strong.

It’s about the ability to keep up with our children and grandchildren. Exercise is very important in aging to maintain independence in daily life with activities such as going to the toilet, getting out of bed and up and off the couch, and going local food shopping. Exercise and physical activity are associated with being able to live independently, and not enter residential care.

So when you’re feeling low, it’s tempting to binge Netflix, or spend hours scrolling through social media comparing other people’s lives to your own, and feeling even sadder. This is especially true for teenagers. The antidote we know clearly from epidemiology and biology is to just move: whether it’s working with a team, going for a long walk, or finding a community gym or yoga class. You will definitely feel more hopeful afterwards.

• Devi Sridhar is chair of global public health at the University of Edinburgh

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