Women who lose weight — and keep it off — after age 50 have a lower risk of breast cancer than women whose weight remains stable, according to a study published this week in the Journal of the National Cancer Institute (JNCI).
The greater the weight loss, the greater the reduction in risk, although the study found that shedding even a small number of excess pounds — as few as 4.5 — lowered the chances of developing breast cancer.
Being overweight or obese is a well-established risk factor for developing breast cancer after menopause. It’s been less clear, however, whether losing excess weight could reverse that risk. This study — the largest on the topic to date — indicates it might.
“Our results suggest that even a modest amount of sustained weight loss is associated with lower breast cancer risk for women over 50,” says Lauren Teras, the study’s lead author and an epidemiologist with the American Cancer Society, in a released statement. “These findings may be a strong motivator for the two-thirds of American women who are overweight to lose some of that weight. Even if you gain weight after age 50, it is not too late to lower your risk of breast cancer.”
For the study, Teras and her colleagues analyzed pooled data collected from 180,885 women aged 50 and older who participated in 10 previous studies conducted in the United States, Australia and Asia. This group of women included enough individuals who successfully sustained a weight loss to make the study’s findings statistically meaningful.
The women had their body mass index (BMI) assessed three times over about 10 years: when they entered their study, about five years later and then again about four years later. The second assessment was used to establish if the women had lost weight, while the final one was used to determine if they had sustained that weight loss.
An analysis of the pooled data found that 20 percent (36,744) of the women maintained a stable weight (within two pounds) over the 10 years. Another 22 percent (39,371) lost weight by the second assessment, but only half of them (19,694) had kept that weight off by the final assessment.
The women were followed for about another eight years. By the end of that period, 6,930 of them (3.8 percent) had been diagnosed with breast cancer.
The researchers then looked for associations between weight fluctuations and breast cancer risk. After adjusting for other factors associated with breast cancer risk, such as level of physical activity and use of hormone replacement therapy, they found that women who lost weight and kept it off were less likely to have developed breast cancer than women whose weight remained stable. The larger the amount of weight loss, the lower the risk.
Specifically, women who lost 4.4 to 10 pounds — and kept it off — were 13 percent less likely to have been diagnosed with breast cancer than women whose weight remained stable, while those who lost 10 to 20 pounds were 16 percent less likely to have developed the disease.
Women who sustained a weight loss of more than 20 pounds had an even greater reduction in risk — a drop of 26 percent.
The likelihood of developing breast cancer was also lower — by 23 percent — among women who lost more than 20 pounds and then regained some (but not all) of it back.
Limitations and implications
This was an observational study, so it shows only an association between weight loss and breast cancer risk, not a cause and effect. Other factors could also explain the results. It could be, for example, that women who lose weight adopt additional healthful habits that lower their risk of breast cancer.
Also, in eight of the 10 pooled studies, participants self-reported their weight, including all losses and gains. Those reports may not have been entirely accurate.
Still, this is the largest and most robust study conducted to date on this topic. Furthermore, its findings have a potential biological explanation. As Teras and her colleagues point out in their paper, other research has shown that weight loss reduces the levels of estrogen circulating in women’s bodies. High levels of estrogen after menopause have been linked to an increased risk of breast cancer.
“We found that losing weight — and keeping it off — was associated with lower breast cancer risk for women aged 50 years and over,” Teras and her co-authors conclude.
“In other words, it is not too late to lower your risk of breast cancer if you have gained weight after age 50,” they add. “Prevention of the most common cancer worldwide may be a particularly motivating factor for the near epidemic numbers of overweight women.”
FMI: You’ll find an abstract of the study on the JNCI website, although the full paper is behind a paywall.