Low-fat dietary pattern and breast cancer mortality by metabolic syndrome components: a secondary analysis of the Women’s Health Initiative (WHI) randomised trial

BACKGROUND In the Women's Health Initiative (WHI) dietary modification (DM) randomised trial, the low-fat dietary intervention reduced deaths from breast cancer (P = 0.02). Extending these findings, secondary analysis examined dietary intervention influence on breast cancer mortality by metabolic syndrome (MS) components. METHODS In total, 48,835 postmenopausal women with no prior breast cancer were randomised to a low-fat dietary intervention or comparison groups. Four MS components were determined at entry in 45,833 participants: (1) high waist circumference, (2) high blood pressure, (3) high cholesterol and (4) diabetes history. Forest plots of hazard ratios (HRs) were generated with P-values for interaction between randomisation groups and MS component score. Primary outcome was death from breast cancer by metabolic syndrome score. RESULTS HRs and 95% confidence intervals (CI) for dietary intervention influence on death from breast cancer were with no MS components (n = 10,639), HR 1.09, 95% CI 0.63-1.87; with 1-2 MS components (n = 30,948), HR 0.80, 95% CI 0.62-1.02; with 3-4 MS components (n = 4,246), HR 0.31, 95% CI 0.14-0.69 (interaction P = 0.01). CONCLUSIONS While postmenopausal women with 3-4 MS components were at higher risk of death from breast cancer, those randomised to a low-fat dietary intervention more likely had reduction in this risk. REGISTRY ClinicalTrials.gov (NCT00000611).