Abstract and Introduction
We examined the association of sedentary behavior with risk of ovarian cancer overall, by tumor subtype, and by participant characteristics in the Nurses' Health Study (NHS) and Nurses' Health Study II (NHS II). A total of 69,558 NHS participants (1992–2016) and 104,130 NHS II participants (1991–2015) who reported on time spent sitting at home, at work, and while watching television were included in the analysis, which included 884 histologically confirmed ovarian cancer cases. Multivariable-adjusted Cox proportional hazards models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for ovarian cancer by sitting time (no mutual adjustment for individual sitting types in primary analyses). We examined potential heterogeneity by tumor histological type (type I or II), body mass index (weight (kg)/height (m)2; < 25 or ≥25), and total physical activity (<15 or ≥15 metabolic equivalent of task–hours/week). We observed an increased risk of ovarian cancer for women who sat at work for 10–19 hours/week (HR = 1.25, 95% CI: 1.04, 1.51) and ≥20 hours/week (HR = 1.40, 95% CI: 1.14, 1.71) versus <5 hours/week. This association did not vary by body mass index, physical activity, or histotype (P for heterogeneity ≥ 0.43). No associations were observed for overall sitting, sitting while watching television, or other sitting at home. Longer sitting time at work was associated with elevated risk of ovarian cancer. Further investigations are required to confirm these findings and elucidate underlying mechanisms.
In 2021, there will be approximately 21,410 incident ovarian cancer cases and 13,770 ovarian cancer deaths in the United States. Despite its poor prognosis,[1,2] relatively few modifiable risk factors for ovarian cancer have been identified. Inflammation is thought to be a key etiological mechanism underlying ovarian cancer development,[3,4] and multiple studies have observed that inflammation-related conditions (e.g., adiposity) and biomarkers (e.g., C-reactive protein) are related to higher risk of ovarian cancer.[5–8] Identification of additional inflammatory risk factors may provide opportunities for prevention.
In the Nurses' Health Study (NHS) and Nurses' Health Study II (NHS II), we previously observed that both moderate (≥27 metabolic equivalent of task (MET)-hours/week) and low (<3 MET-hours/week) levels of physical activity, as compared with limited activity (3–9 MET-hours/week), during the premenopausal period was associated with a higher risk of ovarian cancer, especially for serous/poorly differentiated tumors. Sedentary behavior is defined as any waking behavior characterized by an energy expenditure less than or equal to 1.5 METs while in a sitting, reclining, or lying position. Importantly, sedentary behavior is related to increased inflammation, independently of physical activity, since highly sedentary people can still meet physical activity recommendations.[11–14] Further, sedentary behavior increases the risk of metabolic syndrome, as well as central adiposity and elevated blood glucose and insulin levels, which are related to increased risk of several cancers in adults.[15–19] Sedentary behavior has been associated with an increased risk of ovarian cancer in some, but not all, studies.[20–23] However, most investigators have measured sedentary behavior at 1 time point and have not evaluated whether the association varied by tumor histological type.
Therefore, we used data from 2 prospective studies, the NHS (1992–2016) and NHS II (1991–2015), to examine the association of time-updated sedentary behavior with risk of ovarian cancer overall and by tumor histotype, as well as by body mass index (BMI; weight (kg)/height (m)2) and physical activity, with over 20 years of follow-up.
Am J Epidemiol. 2022;191(6):1021-1029. © 2022 Oxford University Press