Sedentary behavior has been reported to increase the risk of breast cancer. On the other hand, regular exercise and other physical activity is associated with lower risk, including among women who are overweight or obese. This raises the question as to whether a lifestyle that includes long periods of sitting increases the risk of breast cancer even in regular exercisers.
Physical activity is thought to reduce the risk of breast cancer through its influence on circulating sex hormones, insulin sensitivity, inflammation, and weight control. Previous studies have reported that sitting at work compared to more active occupations is associated with increased breast cancer risk. However, this does not determine whether sitting is in and of itself harmful. Now a new study has reported that obese women are not subject to the increased risk of breast cancer associated with prolonged sedentary behavior as long as they are physically active.
Latest research finds exercise mitigates prolonged sitting
The study referenced above was designed to investigate the association between time spent sitting per day and the risk of breast cancer in obese women, taking into account the possible mitigating role of physical activity. To conduct the study, the authors analyzed data concerning obese (BMI ≥ 30 kg/m2) women from the National Health and Nutrition Examination Survey (NHANES) 1999–2020. Results were adjusted for key confounding variables.
The study included a total of 9,706 women with average age 50.3 years, of whom 34.6% were non-Hispanic white, 31.3% were non-Hispanic black, 27.3% were Mexican-American or other Hispanic, and 6.9% other races. Participants were assigned to four groups according to hours of sitting time per day (< 4 (26.6% of participants), 4 to 6 (22.4%), 6 to 8 (29.7%), and > 8 (21.3%)). Breast cancer was reported by 271 of the women (2.8% of participants).
Compared to those with < 4 hours of daily sitting time, those in the group with 4 to 6 hours of sitting time were 1.61 times more likely to have breast cancer, those in the 6 to 8 hour group were 1.86 times more likely to have breast cancer, and those in the > 8 hour group were 2.21 more likely to have breast cancer in the study group overall. However, the detrimental effects of prolonged sitting on breast cancer prevalence were found only in physically inactive women. The results were 0.87, 0.71, and 1.06 for physically active women, compared to 2.56, 2.12 and 2.43 for those who were physically inactive. In fact, there was a positive dose-response relationship between daily sitting time and breast cancer in both the participants in total and physically inactive participants.
Sedentary behavior was found to be more harmful in postmenopausal women who were (1) aged at least 60; (2) non-Hispanic white; (3) better educated, with more than a high school education; and (4) among the more obese (BMI ≥ 35 kg/m2). The authors conclude that prolonged daily sitting time is associated with increased prevalence of breast cancer in obese women; being physically active appears to mitigate this link. Prospective studies are required to further investigate this association, according to the authors.