Leisure Time Sitting Increases Cancer Risk in Women

Pam Harrison

July 14, 2015

Women who sit 6 or more hours a day during their leisure time have a 10% greater risk of developing any cancer compared with women who sit for fewer than 3 hours a day. In addition, they are more likely to develop certain site-specific cancers, such as invasive breast cancer, ovarian cancer, and multiple myeloma.

However, no similar pattern emerged for men.

The findings were published online June 30 in Cancer Epidemiology, Biomarkers & Prevention.

"What this study is showing is that there is an independent benefit of being physically active, even if you are meeting or exceeding physical activity guidelines," lead author Alpa Patel, PhD, epidemiologist at the American Cancer Society, Atlanta, Georgia, told Medscape Medical News.

"So when we think about independent risk factors for many types of cancer, and definitely for invasive breast cancer, you want to tell women to maintain a physically active lifestyle, to maintain a healthy weight, to limit their alcohol consumption, and now you also want to tell them to reduce their time spent sitting," she said.

This adds one more way in which women can take a step towards lowering their overall risk of breast cancer — by sitting less. Dr Alpa Patel

"So this adds one more way in which women can take a step towards lowering their overall risk of breast cancer — by sitting less," Dr Patel said.

Follow-up for More Than a Decade

The findings come from an analysis of data on some 69,260 men and 77,462 women enrolled in the American Cancer Society Cancer Prevention Study II Nutrition.

All participants were cancer-free on enrolment.

Between 1992 and 2009, 18,555 men and 12,236 women were diagnosed with cancer.

On average, men were followed for 13.2 years, and women were followed for an average of 15.8 years.

"In women, leisure-time spent sitting was associated with a statistically significant higher risk of total cancer incidence ([relative risk (RR)]=1.10; 95% [confidence interval (CI)] 1.04-1.17 for ≥6 hours vs. <3 hours/day) after adjustment for physical activity, [body mass index (BMI)], and other potential confounders," the authors report.

Sitting 6 or more hours a day during leisure time was also associated with a 65% greater risk for multiple myeloma, a 43% greater risk for ovarian cancer, and a 10% greater risk for invasive breast cancer compared with women who sat less than 3 hours a day during leisure time.

The association between longer sitting times and endometrial cancer was statistically significant before adjusting for BMI, but was attenuated when adjusted for BMI.

Table. Women Who Sit 6 or More Hours vs Fewer Than 3 Hours a Day During Leisure Time and Site-Specific Cancer Risk

Cancer RR 95% CI/b> Not Adjusted for BMI Adjusted for BMI
Multiple myeloma 1.65 1.07 - 2.54    
Ovarian cancer 1.43 1.10 - 1.87    
Invasive breast cancer 1.10 1.00 - 1.21    
Endometrial cancer     RR, 1.34 (95% CI, 1.08 - 1.67) RR, 1.21 (95% CI, 0.97 - 1.50)

Moreover, the association between an increased overall cancer risk among women who sat 6 or more hours a day was seen among both the most active and the least active women, with risk increased by 14% and 13%, respectively, relative to physically active women who reported sitting less than 3 hours a day.

When the researchers examined exercise activity, BMI, and age, none of the three modified the associations of sitting time with total or site-specific cancer risk, the authors add.

Pattern Not Seen in Men

The same pattern was not seen in men in this study. Leisure time spent sitting was not associated with cancer risk in men, with the exception of an 11% higher risk associated with sitting time among obese men.

"No one study stands on its own, and when we look at the collective body of growing scientific evidence, not every study is seeing this gender difference," Dr Patel observed.

One possible reason investigators are seeing a sex difference in this study is that cancer has a long latency period.

"While the majority of our population is retired, most men in their adult life, especially in this age group, spent time in occupations that may have had more activity accompanying the employment," Dr Patel explained.

"So it could just be that we are not capturing that long-term exposure to activity through adulthood," she added.

Almost all the women in the cohort were retired or were homemakers, so for women, there was a negligible influence of occupation on cancer risk.

"We also analyzed results among women who were currently no longer employed or who were never employed, and the risk estimates really did not change," Dr Patel added.

Dr Patel also noted that obesity is not as strongly correlated with sitting as might initially be thought.

"There are a lot of individuals whom I would describe as 'an active couch potato.' " Dr Patel said. "People are going to the gym and maintaining a healthy weight, but they spend the majority of the rest of their time in sedentary activities — sitting at work, sitting in the car, sitting at home — so you really have to think not just of that 30 minutes a day where you are intentionally engaging in physical activity, but what does the rest of your day look like?"

"And you can add to the benefit of physical activity by reducing the time you spend sitting," she added.

It has been previously been reported that the average life expectancy in the United States would increase by 2 years if excessive sitting time were reduced by 3 hours a day ( BMJ Open. 2012;2:e000828).

The authors have disclosed no relevant financial relationships.

Cancer Epidemiol Biomarkers Prev. Published online June 30, 2015. Abstract


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