New York Times
By Gretchen Reynolds
Science Times: Walking for at least 11 minutes a day could reduce the undesirable health consequences of sitting for hours and hours, according to a helpful new study of the ways in which both inactivity and exercise influence how long we live. The study, which relied on objective data from tens of thousands of people about how they spent their days, found that those who were the most sedentary faced a high risk of dying young, but if people got up and moved, they slashed that threat substantially, even if they did not move much.
For most of us, sitting for prolonged periods of time is common, especially now, as we face the dual challenges of COVID-related restrictions and the shortening, chilly days of winter. Recent surveys of people’s behavior since the start of the pandemic indicate that a majority of us are exercising less and sitting more than we were a year ago.
Not surprisingly, there could be long-term health consequences from this physical quietude. Multiple past epidemiological studies show links between sitting and mortality. In general, in these studies, couchbound people are far more likely to die prematurely than active people are.
But how active an active person should be if he or she hopes to mitigate the downsides of sitting has remained unclear. If you sit for eight hours at work, for instance, then stroll for half an hour in the evening — meaning you comply with the standard exercise recommendation of about 30 minutes of exercise most days — is that enough movement to undo most of the health risks of too much sitting?
Some past research had suggested the answer is no. A 2016 study involving more than a million people found, instead, that men and women needed to exercise moderately for about 60 to 75 minutes a day in order to diminish the undesirable effects of sitting.
That study, though, like most similar, earlier research, asked people to remember how much they had moved or sat, which can be problematic. We tend to be unreliable narrators of our lives, overestimating physical activity and underestimating how much we sit. But if large numbers of people misremember this way, the paradoxical result is that exercise looks less potent than it is, because the studies’ “active” people appear to have needed plenty of exercise to gain health benefits, when the objective amount of exercise they actually completed was less, and this smaller amount produced the gains.
So, for the new study, which was published recently in a special issue of The British Journal of Sports Medicine devoted to the World Health Organization’s updated physical activity guidelines and related research, many of the authors of the 2016 review decided to, in effect, repeat that earlier research and analysis, but, this time, use data from people who had worn activity monitors to objectively track how much they moved and sat.
The scientists wound up gathering results from nine recent studies in which almost 50,000 men and women wore accelerometers. These studies’ volunteers were middle-age or older and lived in Europe or the United States. Combining and collating the nine studies’ data, the scientists found that most of the volunteers sat a lot, averaging close to 10 hours a day, and many barely moved, exercising moderately, usually by walking, for as little as two or three minutes a day.
The researchers then checked death registries for about a decade after people had joined their respective studies and started comparing lifestyles and life spans. Dividing people into thirds, based on how much they moved and sat, the researchers found, to no one’s surprise, that being extremely sedentary was hazardous, with people in the top third for sitting and bottom third for activity having about 260% more likelihood of premature death than the men and women who moved the most and sat the least. (The researchers controlled for smoking, body mass and other factors that might have influenced the results.)
Other combinations of time spent sitting and moving were less alarming, though, and even heartening. People in the middle third for activity, who exercised moderately for about 11 minutes a day, were significantly less likely to have died prematurely than people who moved less, even if all of them belonged to the group that also sat the most.
Crunching the numbers further, the researchers concluded that the sweet spot for physical activity and longevity seemed to arrive at about 35 minutes a day of brisk walking or other moderate activities, an amount that led to the greatest statistical improvement in life span, no matter how many hours someone sat.
Of course, this study was observational and does not prove that exercise caused people to live longer, only that physical activity, sitting and mortality were linked.
But the results strongly suggest that if we sit all day, as so many of us do, we should aim, too, to get up and move, said Ulf Ekelund, a professor of epidemiology and physical activity at the Norwegian School of Sport Sciences in Oslo, Norway, who led the new study. “Brisk walking is excellent moderate exercise,” he said, and, in half-hour stints — or even less — might help to lengthen our lives.
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