(Reuters Health) – Older women who lose weight may have a lower risk of developing invasive breast cancer than those who maintain or gain weight, suggests a large US study.
While obesity has long been linked to an increased risk of breast cancer, previous research has offered a mixed picture of weight loss potential to help reduce that risk. For the present study, researchers evaluated weight and height to calculate the body mass index (BMI) for more than 61,000 women twice, three years apart.
Thus, researchers followed women for an average of 11.4 years longer. During this period, 3,061 women developed invasive breast cancer.
Compared to women who had a stable weight during the first three years of study, women who had lost at least 5% of their body weight during the first three years were 12% less likely to develop breast cancer in the decade following.
"Our results are consistent with a woman who is able to reduce the risk of cancer, even if they remain overweight or obese after losing a bit of weight, since almost none of the women in our current analysis of cohort lost enough weight to reach normal weight. "Study author Dr. Rowan Chlebowski of the National Medical Center of the City of Hope in Duarte, California.
"This should be an encouraging result for women, since a modest weight loss sustained can be achieved by many, while weight loss sufficient to return to a non-obese or overweight category is rather difficult," Chlebowski said via e-mail.
All the women in the study had gone through menopause, when menstruation stopped and the production of the estrogen hormone decreased. After menopause, the main source of estrogen in women is adipose tissue; being overweight or obese can increase the risk of cancer because estrogen can help grow tumors.
"Overweight or obese women have an increased risk of postmenopausal breast cancer due to the increased hormone levels associated with fat cells," said Dr. Daniel Schauer of the University of Cincinnati College of Medicine, who he was not involved in the study.
"These hormones, especially estrogen, can promote the development of postmenopausal breast cancer," Schauer told Reuters Health via e-mail. "Losing weight decreases the levels of circulating hormones".
Among the approximately 41,000 women in the study who had a stable weight during the first 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 with an average BMI of 26.7.
Women who lost weight started heavier.
The approximately 3,300 women who lost weight involuntarily started with a BMI of 27.9 and half of them lost more than 17 pounds. Women who lost weight intentionally started with an average body mass index of 29.9, only a shy 30-year-old BMI to be considered obese, and half of them lost more than 20 pounds.
The weight gain of 5% or more was not associated with an increased risk of breast cancer in general, the researchers report in the journal Cancer. But this amount of weight gain was associated with a 54% greater risk of developing "triple negative" breast cancer, a type of aggressive and difficult to treat cancer.
The study was not a controlled experiment designed to demonstrate whether or how weight changes over time could have a direct impact on women's risk of developing or dying from breast cancer.
The researchers measured only the weight of women twice, at the start of the study and three years later, and any weight changes reported by women after they had not been verified by medical tests.
For most people, weight creeps over time, said Dr. Graham Colditz of the Washington University School of Medicine in St. Louis, who was not involved in the study.
"So the first realistic goals is to work to stop earning.There are health benefits, even if you're overweight," Colditz said via e-mail.
"Afterwards, sensibly and slowly losing weight is a good goal," added Colditz. "From 5 to 10 pounds is a great start that is easier to maintain over time."
SOURCE: bit.ly/2AreUsz Cancer, online 8 October 2018.