A higher body mass index (BMI), especially in early adulthood, may be associated with a reduced risk of breast cancer before menopause, according to an article published in the JAMA.
Previous studies have observed an association between higher body mass index and a lower risk of breast cancer, according to background information in the article. High BMI can be associated with irregular or long menstrual cycles and the development of polycystic ovary syndrome, a condition that occurs when the ovaries malfunction, decreasing fertility and contributing to other illnesses.
All of these are related to disruptions in ovulation, which decrease levels of the hormones estradiol and progesterone; the long-held belief was that these lower levels, in turn, might explain the decrease in breast cancer risk. “However, few studies have explored whether these or other factors provide mechanistic insights into the unexpected protection that a high body mass confers on the premenopausal breast,” the authors write.
“A high BMI during adulthood is highly correlated with a high body mass during adolescence, which may be more important for the development of breast cancer before menopause,” the authors write. “Although a high birth weight has been fairly consistently linked to an increase in the risk of premenopausal breast cancer, the BMI-breast cancer association seems to reverse at some point during the first years of life, only to revert back after menopause,” when breast cancer is most often diagnosed.
Because the failure to ovulate (anovulation) cannot be measured directly, these findings do not rule out the hypothesis that factors related to ovulation contribute to the protective effect of a high BMI. “However, because adjustment for menstrual cycle patterns, infertility due to ovulatory disorder, probable polycystic ovary syndrome and use of oral contraceptives did not even slightly attenuate the association with BMI, anovulation does not seem to be a primary explanation for the reduced risk in heavier women,” the authors conclude
“Among women with no history of infertility due to an ovulatory disorder, the inverse association between BMI and premenopausal breast cancer incidence persisted, lending further support to the role of mechanisms other than anovulation.” The link may be hormonal, or due to the fact that obese women are less likely to be screened for breast cancer. (ANI)