Ahn J et al. (2007) Adiposity, adult weight change, and postmenopausal breast cancer risk. Arch Intern Med 167: 2091–2102

Obesity is a risk factor for postmenopausal breast cancer; it has been suggested that breast carcinogenesis may be initiated and promoted by an increase in production of endogenous estrogens in the adipose tissue. Women who do not use menopausal hormone therapy (MHT) are more susceptible to postmenopausal breast cancer associated with adiposity and adult weight gain, but the effect of the timing and amount of weight gain on breast cancer risk was unknown.

Ahn et al. carried out a prospective study of 99,039 postmenopausal women in the NIH–AARP (American Association of Retired Persons) Diet and Health Study. BMI and weight change at ages 18, 35 and 50 years and at the current age were examined in relation to breast cancer risk. Association of these factors with the effect of MHT was also investigated. The authors found that weight change during the four periods was consistently associated with increased breast cancer risk in MHT nonusers (relative risk [RR], 2.15; 95% CI, 1.35–3.42 for a ≥50 kg weight gain between age 18 years and the current age compared with stable weight) but not in current MHT users. MHT nonusers who were overweight or obese were more likely to develop advanced disease than those using MHT.

The authors concluded that there was no apparent relation between increased cancer risk and weight gain during specific periods in life and suggest that maintaining a healthy weight throughout life may be a useful preventative measure. They highlight that these findings may not apply to all women, as this particular study comprised mainly white women.