(Reuters Health) – Older women who lose weight may have a lower risk of invasive breast cancer than those who maintain or gain weight, a large US study.
While obesity has long been associated with an increased risk of breast cancer, previous research has offered an overview of the various potential weight loss to help reduce that risk. For the current study, researchers assessed the weight and height to calculate the body mass index (BMI) for more than 61,000 women twice, three years.
Then, researchers followed more than 11.4 years for women. During this time 3,061 women developed invasive breast cancer.
Compared to 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 the first three years were 12 percent less likely to develop breast cancer over the next decade or more.
"Our results are consistent with women who are able to reduce their cancer risk, even if they remain overweight or obese after losing weight, because almost no woman in our cohort analysis is currently losing enough weight to achieve normal weight," said study lead author Dr. Rowan Chlebowski from City of Hope National Medical Center in Duarte, California.
"That should be an encouraging result for women because mild weight loss can be achieved by many people, while adequate weight to return to the non-obese category or being overweight is difficult," Chlebowski said via email.
All women in this study have experienced menopause, when menstruation stopped and estrogen production decreased. After menopause, the main source of female estrogen is fat tissue; being overweight or obese can increase the risk of cancer because estrogen can help tumor growth.
"Women who are overweight or obese are likely to have an increased risk of postmenopausal breast cancer due to an increase in hormone levels associated with fat cells," said Dr. Daniel Schauer of the University of Cincinnati College of Medicine, who was not involved in the study.
"These hormones, especially estrogen, can increase the development of postmenopausal breast cancer," Schauer told Reuters Health via email. "Losing weight lowers levels of circulating hormones."
Among about 41,000 women in the study who had stable weight during the first three years, participants had an average BMI of 26.7, which was considered overweight.
12,000 women who gained weight during the study also began with an average BMI of 26.7.
Women who lose weight start to get heavier.
About 3,300 women who lost weight accidentally 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 BMI of 29.9, just shy of a BMI cutoff of 30 to be considered obese, and half of them lost more than 20 kilograms.
Weight gain of 5 percent or more is not associated with an increased risk of overall breast cancer, the researchers report in the journal Cancer. But this amount of weight gain was associated with a 54 percent higher risk of "triple negative" breast cancer, an aggressive and difficult to treat cancer.
This study is not a controlled experiment designed to prove whether or how changes in body weight over time can directly impact the risk of women developing or dying from breast cancer.
Researchers only measured women's weight twice, at the start of the study and again three years later, and any changes in women's body weight were reported afterwards not verified by a medical examination.
For most people, body weight creeps over time, Dr. Graham Colditz from the University of Washington Medical School at St. Louis, who was not involved in this study.
"So, the first realistic goal is to work to stop reaching. There are health benefits to that, even if you are overweight, "Colditz said via email.
"After that, wisely and slowly losing weight is a good goal," Colditz added. "Five to 10 pounds is a good start that is easier to maintain over time."
SOURCE: bit.ly/2AreUsz Cancer, online October 8, 2018.