The Hazards of Sitting - New Scientist

Scientists analysed mortality data from heart disease, diabetes and cancer and found a common culprit: sitting.

Prolonged periods of inactivity killed more than 5 million people every year globally, making the health risks similar to smoking and obesity. Exercise doesn’t fully undo the dangers of sitting. How could evolution produce an organism that responds so poorly to rest?

It would seem… that our bodies should be well-adapted to rest whenever possible, sparing resources for future use. Countless other species seem to be on board with this philosophy. Even our evolutionary cousins, the great apes, spend hours every day sitting and lying about and despite people’s assumptions that hunter-gatherers are more active than people in more industrialized societies, we also know from the Hadza community that they spend lots of time sitting and resting, too. But sitting doesn’t make them sick. What was their secret?

Research comparing postal workers who delivered the mail with their sedentary office mates showed that [they were about 30% more likely to develop coronary heart disease, and to do so at a younger age and with worse outcomes] studies [showed that] people had an elevated risk of heart disease and of dying at an earlier age when they reported sitting for long periods while, for example, watching television, with bed-rest studies, where volunteers would lie down for long periods. Their bones thinned and muscles weakened. Subjects had higher levels of triglycerides in their blood and other risk factors for cardiovascular disease.

When we stand and walk, we engage the muscles of our legs and core to hold us upright. Chairs and beds allow us to turn those muscles off. With no need to support the body, the muscles switched off and stopped burning fuel. This in turn led to reduced levels of lipoprotein lipase [an enzyme, which] acts like a triglyceride vacuum cleaner, breaking the molecules into fatty acids that can be burned in the muscles, and thus removed them from the bloodstream. Prolonged sitting allows us to switch our muscles off and causes triglycerides to climb…. people forced to sit for long periods developed elevated triglyceride levels…if the sitting time is broken up with light activity, even a bit of slow walking, triglyceride levels are greatly reduced.

People asked to reduce sitting by spending more time walking and standing over a 4-day period saw a 32 % drop in triglyceride levels. Sitting for long, uninterrupted periods also alters the walls of blood vessels in ways that make them stiffer and more prone to coronary disease, but breaking up sitting with light activity restores vessel function.

Chairs are a surprisingly recent invention. They first appear in the archaeological record less than 5000 years ago, well after the emergence of farming, towns and metallurgy. Our Paleolithic hunter-gatherer ancestors never had them.

The Hadza don’t use chairs. In societies with little furniture…resting often involved squatting or kneeling on the ground. Deep squatting flexes the foot upward, pressing the talus into the end of the shin bone, or tibia. If it is done often enough, these postures leave a mark on the tibia, called a squatting facet… these facets [are found] on fossils of human ancestors going back to Homo erectus, nearly 2 million years ago.

In the Hadza… people of all ages spent much of their resting time in a deep squat, heels on the ground, bottoms resting on the back of the ankles. If you don’t grow up doing it, you have probably lost the flexibility to squat that deeply…rather than sitting less or breaking up their sitting into shorter bouts, perhaps the secret was in the way they sit… [with testing] Hadza spent nearly 10 hours every day resting, almost identical to the numbers for people in the US, Netherlands and Australia. The number of breaks was similar across populations as well. Still, Hadza blood profiles and blood pressures showed they were remarkably healthy, with low levels of triglycerides and other markers of heart disease. The big difference was in muscle activity during rest.

Squatting forces you to keep the body balanced over the feet, requiring between 5 and 10 times as much muscle activity in the legs as sitting in a chair or on the ground, and sometimes even more muscle activity than we would expect from light activity. Hadza were squatting and kneeling nearly one-third of this time… the use of ‘active resting’ postures, like squatting and kneeling, might maintain enough muscle activity to prevent triglyceride build-up and avoid disease. If our ancestors also used these more active rest postures, then the negative health effects of sitting make perfect sense: our physiology never experienced long periods of quiet muscles, so our bodies never evolved a protective response… you can improve your cardiovascular health by sitting less, and by breaking up your sitting into shorter bouts to increase muscle activity throughout the day.

New Scientist (18 July 2020)