Among the list of health problems that can come of too much sitting, a new one emerges: Cancer.
Sitting for extended periods of time has been a sort of 21st century epidemic – TV-gazing isn’t new, but streaming movies and tablets aren’t helping our habit of sitting. In studies, sedentariness has been connected to obesity, metabolic syndrome, cardiovascular disease and diabetes; it’s even linked to an earlier death. Now, a new study in the Journal of the National Cancer Institute suggests that sitting is also connected to cancer – not all types, but to colon and endometrial (uterine) cancer. And it’s not just because sitting takes us away from exercising – even those whosit a lot and exercise have an increased risk for these cancers. This means that there’s something intrinsic about the unhealthiness of sitting apart from lack of exercise.
To study this question, the team from University of Regensburg carried out a meta-analysis of 43 earlier studies, including over 4 million people. The studies had all periodically queried the participants on how much time they spent sitting – TV-related sitting, occupational sitting, and total sitting time. Over the years, there were almost 69,000 cancer cases.
The more a person sat, the higher the cancer risk for two types of cancer: Endometrial and colon. Sedentariness was linked to a 24% increased risk of colon cancer and a 32% higher risk of developing endometrial cancer. For every two-hour increase in overall sitting time, the risk of cancer rose 8% for colon cancer and 10% for endometrial cancer (it rose 6% for lung cancer, but the association was just borderline).
On the upside, breast, rectal, ovarian, prostate, stomach, esophagus, testicular, kidney, and non-Hodgkin lymphoma were not linked in any way to sitting.
Of course, the famously bad pastime of sitting-while-watching-TV was associated with the greatest risk: a 54% increased risk of colon cancer and 66% higher risk for endometrial cancer. But it’s very likely that body weight plays a role here, since TV-watching is often accompanied by snack foods and soda – and weight is a known risk factor for certain cancers (more on this below).
“We found that TV viewing was associated with an increased risk of cancers of the colon and the endometrium,” says lead author Daniela Schmid. “We further observed that the results were independent of physical activity, showing that sedentary behavior represents a potential cancer risk factor distinct from physical inactivity.”
And this last point she makes is the more striking finding – that the connection between sitting and cancer was evident regardless of the exercise a person got. In other words, even people who sat a lot and exercised had the elevated risk. This means that there’s something intrinsically bad about sitting, apart from lack of exercise.
What are the mechanisms that could possibly explain this? Schmid tells me that part of the connection could certainly be mediated by body weight. “Obesity may mediate carcinogenesis through several pathways, including insulin resistance…and low-grade systemic inflammation,” she says. She adds that in postmenopausal women, fat tissue represents the main source of estrogen; overweight and obesity are a well-known risk factors for endometrial cancer.