Being more physically active has long been known to both slash the risk of cancer and help improve survival in people who already have it — but research is also zeroing in on a simpler target, with possible anticancer benefits of its own: sitting less.
For certain cancers such as breast cancer, spending lots of time sitting has been linked to a higher risk, said Neil Iyengar, section chief of breast medical oncology and director of survivorship services at Winship Cancer Institute at Emory University. “Oftentimes, excessive sitting can just be a reflection of low physical activity and poor lifestyle overall,” he explained, which elevates risk. But emerging evidence suggests sitting, in and of itself, may be a risk factor, too.
One of the first studies on this topic, published in 2015, found that in a group of more than 77,000 women, those who sat for six hours or more a day had a 10 percent greater risk of getting any type of cancer — as well as a 10 percent higher risk of invasive breast cancer — than those who sat for less than three hours a day. And the association held even when researchers accounted for factors such as body weight and amount of physical activity.
Since then, a handful of studies have uncovered a similar link, connecting sedentary time at work to higher breast cancer risk; and prolonged sitting time (of greater than four hours daily) to higher prevalence of breast cancer among women with obesity. Research published in July also suggests that breaking up sedentary behavior — into periods of less than 30 minutes, with movement sprinkled in between — may negate the cancer risks tied to sitting.
All of this evidence is observational, so it can’t prove that sedentary time causes breast cancer nor that avoiding sitting directly lowers risk. The tie between full-fledged exercise and reduced breast cancer risk is more “strongly established,” said Alpa Patel, senior vice president of population science at the American Cancer Society and lead author on the 2015 sitting study above. But what the sitting research suggests is that anything you can do to avoid a long sedentary stretch (for instance, standing or moving around intermittently) may be worth it.
Read on to learn why ample time spent sitting could up your breast cancer risk and how to potentially mitigate it without quitting your day job.
The connection between sitting and breast cancer risk
Researchers are still digging into the why behind sitting and breast cancer risk, but there are several possible explanations for the link.
For starters, a more sedentary lifestyle is linked with chronic low-grade inflammation, Iyengar said, which is an established risk factor for cancer. While small amounts of inflammation are normal and healthy, getting stuck in this state can prompt cells to multiply more rapidly than usual and may contribute to the development of a tumor.
Additionally, low-grade inflammation “may stimulate the fat cells in breast tissue to produce more estrogen,” Iyengar said, which is the hormone that fuels most breast cancers (called estrogen- or hormone-receptor positive breast cancer).
Lots of time spent sitting may also raise your estrogen level, or change how estrogen is metabolized, leaving you with more “free” or biologically active estrogen that can trigger hormonal effects. By contrast, movement can help lower your estrogen exposure over time, Patel said.
Sitting for long stretches can also contribute to insulin resistance. When your muscles contract less often, they soak up less glucose from your blood, prompting your pancreas to pump out more insulin. “Brief periods of high insulin help you get rid of excess sugar and fat,” Iyengar said. But over time, it can cause your cells to become less sensitive to insulin. “Chronic low-grade insulin resistance can cause DNA damage, and damaged DNA can give rise to cancer cells,” he explained.
Finally, there’s the possible impact of sitting on body composition. It may not just contribute to weight gain but could also cause the body to store more energy as fat tissue, Iyengar said. High body fat can raise breast cancer risk even in women with a healthy body weight.
Easy ways to sit less and possibly lower your breast cancer risk
The simplest way to reduce sitting time, particularly if you have a job that requires you to sit, is to punctuate your day with standing, even if it’s just to pace back and forth a few times between tasks. Getting up to stretch your legs and do a simple exercise in place counts, too, as does taking a phone call while folding laundry or unloading the dishwasher, instead of at your desk, if you work from home.
Whenever Patel gets a few minutes of free time, for instance because of a call that ended early, she stands and does 10 calf raises to get her blood flowing before sitting back down. Iyengar recommends actively building in a few mini-breaks for movement throughout each day.
Research suggests working in bursts of high-intensity activity can help you reap the biggest benefit: Jogging up and down the stairs for three minutes, for example, has been shown to reduce the risk of 13 different cancers including breast cancer. The study mentioned above on the benefits of breaking up sedentary behavior found that doing just five minutes of vigorous physical activity (e.g., brisk walking, running) was tied to a 22 percent lower risk of dying from cancer than spending the same amount of time sitting.
Still, it’s also important to keep in mind the benefits of consistent movement, not just sitting less. After all, robust literature ties greater physical activity to reduced risk for seven different types of cancer including not just breast but also colon, endometrial, bladder, stomach, kidney and esophageal. The American Cancer Society suggests aiming for 150 to 300 minutes per week of moderate intensity activity — walking at a 20-minute-mile pace, dancing or sports that get your heart rate up a bit — or 75 to 150 minutes of vigorous activity such as running or swimming.
“But that doesn’t mean you have to hit these benchmarks to get any benefit,” Patel said. “The more you get, the greater the benefit,” she noted, and “something is always better than nothing.”
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