Older women who lose weight may have a lower risk of developing invasive breast cancer than those who maintain or gain weight, a large U.S. study from the City of Hope National Medical Center in Duarte, California suggests.
While obesity has long been linked to an increased risk of breast cancer, previous research is not clear on the potential for losing weight to help reduce the risk.
For the current study, researchers assessed weight and height to calculate body mass index (BMI) for more than 61,000 women twice, three years apart.
Then, the researchers followed these women for an average of 11.4 more years. During this time 3,061 women developed invasive breast cancer.
Losing 5% of body weight protective
Compared with women who had stable weight during the initial three years of the study, women who lost at least 5 percent of their body weight during those first three years were 12 percent less likely to develop breast cancer over the next decade.
The results are consistent with a woman being able to lower her breast cancer risk, even if she remained overweight or obese after losing some weight, since almost none of the women in the study lost enough weight to achieve normal weight.
After menopause, a women’s main source of estrogen is fat tissue; being overweight or obese can increase the risk of cancer because estrogen can help tumors grow.
Among the roughly 41,000 women in the study who had a stable weight during the initial three years, participants had an average BMI of 26.7, which is considered overweight.
The 12,000 women who gained weight during the study also started out with an average BMI of 26.7.
Women who lost weight started out heavier.
The roughly 3,300 women who lost weight unintentionally started out with a BMI of 27.9 and half of them lost more than 17 pounds. Women who lost weight intentionally began with an average BMI of 29.9, just shy of the cut-off BMI considered obese, and half of them lost more than 20 pounds.
Gaining weight over time linked to aggressive breast cancer
Weight gain of 5 percent or more was not associated with an increased risk of breast cancer overall. But this amount of weight gain was associated with a 54 percent higher risk of developing “triple negative” breast cancer, an aggressive and difficult to treat type of cancer.
The study wasn’t a controlled experiment designed to prove whether or how weight changes over time impact a women’s risk of developing or dying from breast cancer.
For most people, weight creeps up over time, so, the first realistic goal is to work to stop gaining weight. There are health benefits to that, even if you’re overweight,” Colditz said by email.
Source: Cancer, online October 8, 2018.
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