Excess Fat Increases Breast Cancer Risk Even with a Normal Body Mass Index

Overweight and obesity are now undoubtedly known to increase cancer risk generally. New research highlights a more specific aspect: a study presented at the American Association for Cancer Research’s Obesity and Cancer Conference found that postmenopausal women’s body fat increased breast cancer risk independently of body mass index (BMI) .

Before menopause, ovaries are the main estrogen source; afterward, it is fat tissue. Body mass index, expressing the relationship between weight and height, is the most common overweight measure. However, because it cannot separately measure muscle, bone and fat, it is not a precise method for determining total body fat. The technology called [dual energy X-ray absorptiometry (DEXA)] specifically measures fat, allowing a more accurate assessment of total body fat.

The study analyzed women aged 50 – 79, totaling 3460. Their BMI was normal (18.5 to 25), with no prior breast cancer. During 16 years of follow-up, 182 developed breast cancer (146 hormone-positive).

According to the study results:

• Despite normal BMI, women with high versus low body fat had approximately double the risk of hormone (estrogen)-positive breast cancer;
• Every 5-kilogram increase in body fat increased estrogen-positive breast cancer risk by 35%;
• Also, physical activity was lower in women with more body fat.

Researchers warn women about overweight and possible increased breast cancer risk from body fat. A limitation is that changes in body fat over time could not be analyzed in relation to risk. The study involved postmenopausal women and cannot be generalized to other women or cancers.

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