Girls with a higher body mass index (BMI) during childhood are less likely than their peers with a lower BMI to develop breast cancer in adulthood , both before and after menopause, according to a study by more than 173,000 women in Denmark, presented at the European Congress on Obesity (ECO).
The findings contrast with those for adult BMI, which indicate that women who gain weight after menopause are at increased risk for postmenopausal breast cancer. While the authors aren’t sure why children with higher BMIs appear to be protected from breast cancer, they caution that being overweight or obese can have many adverse impacts on overall health .
The researchers analyzed data from 173,373 women from the Copenhagen School Health Records Registry born between 1930 and 1996 (age 25 to 91 today) who had information about height and weight measured in annual school health exams from 7 to 13 years. Breast cancer cases were identified by linking to the Danish Cancer Registry.
During an average of 33 years of follow-up, 4,051 women before menopause (at age 55 or younger) and 5,942 women after menopause (after age 55) were diagnosed with breast cancer .
The analyzes suggest "inverse associations" between childhood BMI and breast cancer risk before and after menopause, meaning that breast cancer risks decreased as BMI increased. For example, when comparing two 7-year-old girls with an average height and a z-score difference in BMI (equivalent to 2.4 kg), the girl with the highest BMI had a 7% lower risk of developing breast cancer premenopausal and a 10% lower risk of developing postmenopausal breast cancer than the girl with a lower BMI .
The authors say that more studies are needed to discover the mechanisms underlying these associations. They acknowledge that the findings are only associations , so no conclusions about cause and effect can be drawn, and point to several limitations, including that the study used BMI as a marker of fat mass, but children with the same BMI may have different body fat distributions.