The findings contrast with those for adult BMI, which indicate that women who gain weight after menopause have an increased risk of postmenopausal breast cancer.
A study of more than 173,000 women in Denmark suggests that girls with a higher body mass index (BMI) during childhood are less likely than their peers with a lower BMI to develop breast cancer as adults, both before and after menopause.
The findings contrast with those for adult BMI, which indicate that women who gain weight after menopause have an increased risk of postmenopausal breast cancer. Although the study authors are unsure why children with a higher BMI appear to be protected against breast cancer, they caution that having overweight or obesity can have many adverse impacts on general health.
"Our results suggest that having a higher BMI during childhood may lower your risk of breast cancer both before and after the menopause. But we must be really clear that weight gain should not be considered as a way of preventing breast cancer," said lead author Dorthe Pedersen, MD, from Bispebjerg and Frederiksberg Hospital, Copenhagen, Denmark, in a press release. "There are so many health risks linked with having overweight or obesity, it is vital for women to maintain a healthy weight throughout their lives."
Previous research has established a link between increased BMI in adult women and a lower risk of breast cancer before menopause, but an increased risk after menopause. Although a high childhood BMI may be protective against the risk of overall breast cancer, past studies had not been large enough to investigate the link by type menopausal status.
The researchers analyzed data for 173,373 women from the Copenhagen School Health Records Register born between 1930 and 1996 (between 25 and 91 years of age) who had information on height and weight measured at annual school health examinations from 7 to 13 years of age. Cases of breast cancer were identified by linking with the Danish Cancer Registry.
During an average of 33 years of follow-up, 4051 women were diagnosed with breast cancer before menopause (55 years of age or younger) and 5942 women were diagnosed after menopause (after 55 years of age or younger).
The findings suggest inverse associations between childhood BMI and breast cancer risk before and after menopause, which means that breast cancer risks decreased as BMI increased, according to the study.
The authors note that further research is needed to uncover the mechanisms underlying these associations. Further, they acknowledge that the findings are associations only, so no conclusions can be drawn about cause and effect. There are also a few study limitations, including that the study used BMI as a marker of fat mass, but children with the same BMI can have different body fat distributions and overall levels of body fat, according to the authors.
Higher BMI in childhood may help protect women against breast cancer in later life, both before and after the menopause. EurekAlert! Published May 9, 2021. Accessed May 10, 2021. https://www.eurekalert.org/pub_releases/2021-05/eaft-hbi050621.php