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Breast Cancer Health Center

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Obesity Increases Breast Cancer Risk

Belly Fat, Hip Fat -- All Body Fat Increases Risk

Confirming Risks From Obesity, HRT continued...

Among postmenopausal women:

  • Weight at the start of the study was the strongest predictor of the risk of breast cancer. The researchers found a 65% increase in the risk of breast cancer for women in the highest weight category compared with women in the lowest weight category.
  • Being overweight or obese (a BMI of more than 25) was a strong risk factor for breast cancer -- increasing risks by more than 30%.

  • Among women who had used hormone replacement therapy (HRT) during the study period, body fat was inversely associated with the risks of breast cancer. In other words, the researchers showed that obese postmenopausal women who were using HRT had a 34% reduction in breast cancer risk, compared with lean women.

Among premenopausal women:

  • Weight and BMI did not significantly affect risk.
  • Those with the largest hips had a 70% increased risk of breast cancer. Those with the biggest waist had an 81% increased risk in breast cancer risk.

"[Body size] was more strongly associated with breast cancer risk in post-menopausal than in pre-menopausal women," writes Lahmann. Her results support the theory that excess estrogen exposure increases a woman's breast cancer risk.

Also, tall women were more likely to develop breast cancer -- whether before or after menopause, she notes. Factors that influence height, like bone growth, may also influence breast cancer. Birth weight, diet, and infections during fetal development or in childhood could play a role.

In premenopausal women, obesity creates irregular menstrual cycles and more fertility problems, she explains. These women are likely having fewer ovulation cycles, which means they have less cumulative exposure to estrogens -- thus they have less breast cancer risk.

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