A “favorable” lifestyle was associated with a reduced risk of breast cancer even among women at high genetic risk for the disease in a study of more than 90,000 women, researchers reported.
The findings suggest that, regardless of genetic risk, women may be able to reduce their risk of developing breast cancer by getting adequate levels of exercise; maintaining a healthy weight; and limiting or eliminating use of alcohol, oral contraceptives, and hormone replacement therapy.
of the University of Manchester (England), and colleagues these findings in JAMA Network Open.
With almost a quarter of breast cancers thought to be preventable in the United Kingdom, “it is important to understand the contribution of modifiable risk factors ... and how they affect or add to the inherited genetic factors,” the researchers wrote.
To that end, the team reviewed 91,217 white, postmenopausal women in the United Kingdom Biobank, an ongoing longitudinal study of the contribution of genetic, environmental, and lifestyle risk factors in disease. There were 2,728 women who developed breast cancer at a median follow-up of 10 years.
The investigators used a polygenic risk score to categorize subjects as low, intermediate, or high genetic risk. The score was constructed using 305 single-nucleotide variants.
Within each risk group, the researchers divided women by the presence or absence of five lifestyle factors previously associated with a lower risk of breast cancer: healthy weight, regular exercise, no use of hormone replacement therapy beyond 5 years, no oral contraceptive use, and alcohol intake no more than twice a week.
Women with four or more of these factors were deemed to have a favorable lifestyle. Women with two or three factors had an intermediate lifestyle, and women with fewer factors had an unfavorable lifestyle.
The data showed an association between breast cancer and a body mass index of 25 or higher (relative risk, 1.14), no regular physical activity (RR, 1.12), alcohol intake at least three times per week (RR, 1.11), and use of hormone replacement therapy for 5 or more years (RR, 1.23). History of oral contraceptive use was not associated with breast cancer risk (RR, 1.02), but this factor remained a part of the lifestyle classification.
In the low genetic risk group, an intermediate lifestyle (hazard ratio, 1.40; 95% CI, 1.09-1.80) and an unfavorable lifestyle (HR, 1.63; 95% CI, 1.14-2.34) were both associated with a higher risk of breast cancer, compared with a favorable lifestyle.
In the intermediate genetic risk group, intermediate (HR, 1.37; 95% CI, 1.12-1.68) and unfavorable lifestyles (HR 1.94; 95% CI, 1.46-2.58) were again associated with higher breast cancer risk, compared with a favorable lifestyle .
Even in the high genetic risk group, intermediate (HR, 1.13; 95% CI, 0.98-1.31) and unfavorable lifestyles (HR, 1.39; 95% CI, 1.11-1.74) were associated with increased breast cancer risk. Results were adjusted for both age and family history.
In the end, “a healthier lifestyle ... appeared to be associated with a reduced level of risk for [breast cancer], even if the women were at higher genetic risk,” the researchers wrote. “Our findings suggest that women may be able to alter or reduce their risk of developing [breast cancer] by following healthier lifestyles,” regardless of genetic predisposition.