Spending most of your time sitting may boost your risk of certain cancers by an astonishing 66 percent, according to a study conducted by researchers from the University of Regensburg, Germany, and published in the Journal of the National Cancer Institute on June 16.
Significantly, more time spent seated increased cancer risk regardless of how much time a person also spent exercising.
“That sedentariness has a detrimental impact on cancer even among physically active persons implies that limiting the time spent sedentary may play an important role in preventing cancer,” the researchers wrote.
The researchers reviewed the results of 43 observational studies including a total of 4 million participants and 68,936 cancer cases. They found that people who spent the most time sitting had a 66 percent higher cancer risk than people who spent the least time sitting. The cancers most affected were those of the colon, lung and endometrium (uterine lining).
For every two extra hours that a person spent seated, their risk of lung cancer increased 6 percent, their risk of colon cancer increased 8 percent and their risk of endometrial cancer (for women) increased 10 percent.
This increased risk was unaffected by how much time a person spent exercising — time spent seated appeared to be an independent risk factor. Cancer risk was highest, however, among those who spent most of their seated time watching television (compared with those who sat while engaged in other activities). The researchers suggested that unhealthy eating habits during television viewing might partially explain this finding.
Although the lung cancer results were only on the borderline of statistical significance, results for the other cancers were more conclusive.
The study “support[s] a causal relation between sedentary behavior and both colon and endometrial cancers,” wrote Lin Yang and Graham A. Colditz, MD, DrPH, of Washington University in an accompanying editorial.
A sedentary lifestyle is considered a growing public health concern. Previous studies have shown that spending an average of six hours per day watching television can shorten your life by five years.
In the United States and the United Kingdom, less than half of all adults now meet the World Health Organization’s minimum physical activity recommendations. Indeed, adults in those countries spend an average of 90 percent of their leisure time seated.
Colditz blames the trend, in part, on modern technology.
“We accumulate sedentary time from sitting at school or work, motorised transport, watching TV, computer gaming, and so on,” he said.
Although it remains unclear why sedentary time increases health risks even among people who exercise, researchers do know that a sedentary lifestyle tends to produce health risk factors such as obesity and high blood levels of cholesterol, triglycerides and glucose. All these have been linked to cancer risk.
“Time spent sedentary displaces light intensity physical activity, causing decreased energy expenditure accompanied by weight gain and obesity, which are related to increased risk of cancer,” the researchers wrote.
But even people who need to spend all day at a desk for their jobs can still reduce their cancer risk, the researchers noted, by finding ways to break up the time that they spend seated.
“For example, instead of calling your colleagues on the phone or sending emails, you may walk down the aisle or take the stairs to reach their office,” researcher Dr. Daniela Schmid said.
In addition to just getting out of your chair, more exercise is always a good idea, Schmid suggested.
“If people are not warm to a morning jog, then walking or bicycling to the workplace, or inserting a brisk lunchtime walk may bring benefits for your health.”
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