A new analysis has shown that overweight and obese women are at increased risk of developing breast cancer after menopause, compared to normal-weight women.
According to Reuters, for the new study, published in JAMA Oncology, the researchers looked at data on 67,142 post-menopausal women ages 50 to 79 years old from across the US, and followed them for an average of 13 years. Overall, there were 3,388 breast cancers detected by 2010.
The study team grouped women by their body mass index (BMI), a measure of weight in relation to height.
A BMI of less than 25 is considered normal, BMI between 25 and 30 is considered overweight and over 30 is obese, while a BMI of 35 is considered severely obese.
About 5% of women in each weight group were diagnosed with an invasive breast cancer during the study period, but the risk of breast cancer increased with weight.
Women with BMIs of 35 and up (severely obese) were about 56% more likely to be diagnosed with any type of invasive breast cancer during the study, compared to normal-weight women.
Looking at specific breast cancer subtypes, they found the most-obese women were 86% more likely than normal-weight women to be diagnosed with breast tumors that are fueled by the hormones estrogen and progesterone.
Furthermore, the analysis revealed that normal-weight women who gained more than 5% of their starting weight over the study period had a 35% increased risk of breast cancer.
But for women who were already overweight or obese, losing weight did not lower their increased breast cancer risk.
According to study lead, Marian Neuhouser, of the Cancer Prevention Program at the Fred Hutchinson Cancer Research Center in Seattle, "it is important to note that this was not a weight loss trial"
She further said that a research trial looking specifically at whether weight loss decreases breast cancer risk is needed to determine if it's helpful for women.
Co-author, Dr. Clifford Hudis also added that research needs to find out why increased weight may increase breast cancer risk so that solutions can be found.