We are often in awe of the evolutionary adaptations of wild animals who seem so perfectly suited to their evolutionary niche, whether it is the speed of a predator, the physiological efficiency of a desert dwelling animal, or the nest building of exotic birds. It is easy to forget that we too are the product of a history of surviving in hostile environments. We evolved to survive by hunting and gathering over vast distances, we have had to defend ourselves against predators, and we have had to withstand climate changes over millennia.
Whilst our brain power helps us to adapt to a variety of environments in a way that other animals simply cannot, our bodies are never-the-less as impressive as any other in the natural world. Not only do our bodies survive but they actually thrive when put under stress. We see this every day as people who regularly stress their bodies through exercise become fitter and stronger. Not only this, but our mental health improves with exercise. We are psychologically designed to respond positively to the physical stress that has been a necessity of survival for so much of human history. By feeling good after periods of physical activity our ancestors were consistently motivated to go and seek food by more than just the fear of starvation.
The way we live now is very abnormal in the context of our evolutionary history. As we have made our world more manageable the need for us to be active has steadily diminished. Take, for example, a study amongst the Hadza people, one of the last hunter-gatherer societies on Earth who live in Northern Tanzania. The study showed that Hadza people typically engage in 14 times as much moderate to vigorous physical activity than people living in developed societies. As a consequence, rates of heart disease amongst the Hadza are extremely low, with low rates of high blood pressure and very low levels of blood cholesterol.
Contrast the life of hunting with poisoned tipped arrows in the plains of Africa to life in the UK where the average working aged adult spends 9.5 hours sitting every day, rising to more than 10 hours for people between the ages of 65 and 74. In fact, in the UK, about a quarter of adults achieve less than 30 minutes of physical activity each week.
Being active is protective against cardiovascular diseases such as heart attacks and strokes, certain types of cancer, type 2 diabetes, and a range of musculoskeletal problems. Conversely, being inactive is thought to be responsible for around 25% of breast and colon cancer, 27% of diabetes and about 30% of the ischaemic heart disease burden in developed societies. Overall, physical inactivity is thought to be responsible for up to 10% of non-infectious disease worldwide which puts it on a par with smoking and obesity in terms of risk to health. This represents millions of extra, early deaths every year due to physical inactivity.
Whilst many of us try to undo the negative effect of our sedentary lives by introducing intense bursts of exercise into our routines, such as going to the gym, research is beginning to suggest that this is not enough. In fact, only the top quarter of exercisers can undo the negative effect of prolonged periods of sitting. Perhaps even more alarming is the damage done by watching too much TV, which seems to be peculiarly bad for your health. One study combining data from over 1 million people demonstrated that there is an excess mortality associated with watching more than 3 hours each day that cannot be undone no matter how active you are otherwise. To state this more plainly; if you watch more than 3 hours of TV each day you put yourself at risk of dying younger no matter how much time you spend in the gym.
Our physical health and our mental health are inextricably linked. It is well recognized that levels of depression are higher in those suffering with chronic physical health conditions such as diabetes or heart disease so clearly any measure we can take to avoid physical ill health will help safeguard our mental health but, more than this, there seems to be an intrinsic link between physical activity and happiness.
There is strong evidence that exercise is as effective, if not more effective, than standard treatments for depression such as psychological therapy and antidepressants. In fact, the mechanism by which exercise seems to improve mental health mirrors the mechanism of antidepressants by increasing levels of the neurotransmitters serotonin, dopamine and noradrenaline and by actually increasing the size of areas of the brain, such as the hippocampus and amygdala, that shrink in people suffering with depression. Interestingly, the positive of effects of exercise persist through time in a way that the positive of effects of antidepressants do not.
Even at times of life when we normally expect people to reduce their levels of exercise, we can see that maintaining or increasing that level of activity could do much good. For example, physical activity has been shown to reduce the incidence and severity of post-natal depression and mental health problems during pregnancy. Similarly, physical activity has been shown to be a useful treatment for major depression in the elderly whilst also improving their physical health and their independence.
Put simply; we should never stop being physically active.
Overall, as little as 60 minutes of physical activity could be enough to prevent up to 12% of cases of depression. With depression being such a common condition, a reduction of this magnitude could prevent millions of cases of depression across the world, reducing the personal, societal, and economic burden of this illness enormously as well as bringing about a huge reduction in the number of unhappy people living miserable days.
Our sedentary lives represent a genuine public health crisis. We are living shorter, more sickly, and more unhappy lives because we are so inactive. Surely it is time then to treat inactivity in the same, public-health centered way, as we treat smoking, drugs and alcohol use.
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