Obesity, weight gain, and height
Obesity is associated with increased mortality from ovarian cancer. In cohort studies, height and body mass index (BMI),[16,17] including high BMI during adolescence, were associated with an increased risk of ovarian cancer, suggesting a role for diet and nutrition during the adolescent period. The California Teachers Study Cohort (277 cases of ovarian cancer) observed an increased risk of ovarian cancer associated with a weight gain of more than 40 pounds (but not BMI) (RR, 1.8; 95% CI, 1.0–3.0) compared with women who had a stable adult weight and who never used hormone therapy.
Factors With Adequate Evidence of a Decreased Risk of Ovarian Cancer
A collaborative analysis was performed of individual data from 23,257 women with ovarian cancer and 87,303 women without ovarian cancer from 45 studies in 21 countries. The studies included 13 prospective studies, 19 population-based case-control studies, and 12 hospital-based case-control studies. Oral contraceptive use was associated with a dose-response effect by duration of use, with no observed changes in risk reduction by decade of use from the 1960s to 1980s, over which time the amount of estrogen in oral contraceptives was approximately halved. No risk reduction was observed for women who used oral contraceptives for less than 1 year. The risk reduction associated with use from 1 to 4 years, 5 to 9 years, 10 to 14 years, and 15 years or more was 0.78 (99% CI, 0.73–0.893), 0.64 (99% CI, 0.59–0.69), 0.56 (99% CI, 0.50–0.62), and 0.42 (99% CI, 0.36–0.49), respectively. The observed risk reduction persisted after cessation of oral contraceptive therapy but attenuated over time since last use. The proportional reduction in risk per 5 years of use was 29% (95% CI, 23%–34%) for women who had discontinued use within the last 10 years; the reduction in risk was 15% (95% CI, 9%–21%) for women who discontinued use 20 to 29 years ago.