11 December, 2017:
Many studies link weight/body mass index (BMI) to breast cancer risk. However, BMI affects risk differently before and after menopause. Before menopause, being overweight or obese modestly decreases breast cancer risk whereas, after menopause, being overweight or obese increases breast cancer risk. Several recent studies have shed light on other relevant perspectives of this link. The Women's Health Initiative trial provided data on the potential association between the metabolic syndrome and breast cancer risk . The evaluated parameters were: blood glucose, triglycerides, HDL cholesterol, blood pressure, waist circumference, and BMI. Women were then classified into six metabolic obesity phenotypes according to their BMI: 18.5 – < 25, 25 – < 30, > 30 kg/m2) and presence of the metabolic syndrome (> three of the following: waist circumference > 88 cm, triglycerides > 150 mg/dl, HDL cholesterol < 50 mg/dl, glucose > 100 mg/dl, and systolic/diastolic blood pressure > 130/85 mmHg or treatment for hypertension). The cohort included about 21,000 postmenopausal women and over 15 years of follow-up; 1176 cases of invasive breast cancer were diagnosed. Obesity, regardless of metabolic health, was associated with increased risk of breast cancer. Being obese and metabolically unhealthy were associated with the highest risk: HR 1.62, 95% CI 1.33–1.96. These associations were stronger in women who had never used hormone therapy. The investigators concluded that, beyond BMI, metabolic health should be considered a clinically relevant and modifiable risk factor for breast cancer.
What about weight changes? Does weight gain increase the risk? Contrarily, will weight loss help to lower the risk of breast cancer? The Nurses' Health Study demonstrated, in a huge cohort, that weight gain after the age of 18 years was unrelated to breast cancer incidence before menopause, but was positively associated with incidence after menopause . This increased risk with weight gain was limited to women who never used postmenopausal hormones; among these women, the relative risk (RR) was 1.99 (95% CI 1.43–2.76) for weight gain of more than 20 kg vs. unchanged weight (p for trend < 0.001). Furthermore, the percentage of postmenopausal breast cancer accounted for by weight gain alone was approximately 16%. The Nurses' Health Study also presented data on the opposite case scenario, namely on weight loss and breast cancer risk . Women who had never used postmenopausal hormones, lost 10.0 kg or more since menopause, and kept the weight off were at a lower risk than those who maintained weight (RR 0.43, 95% CI 0.21–0.86; p = 0.01 for weight loss trend).