Association between low levels of 1,25-dihydroxyvitamin D and breast cancer risk

Objective: To determine if blood levels of 25- hydroxyvitamin D ( 25- D) or its active metabolite, 1,25- dihydroxyvitamin D ( 1,25- D), are lower in women at the time of first diagnosis of breast cancer than in comparable women without breast cancer. Design: This was a clinic- based case- control study with controls frequency- matched to cases on race, age, clinic and month of blood drawing. Setting: University- based breast referral clinics. Subjects: One hundred and fifty- six women with histologically documented adenocarcinoma of the breast and 184 breast clinic controls. Results: There were significant mean differences in 1,25- D levels ( pmol ml - 1) between breast cancer cases and controls; white cases had lower 1,25- D levels than white controls ( mean difference6SE: - 11.0860.76), and black cases had higher 1,25- D levels than black controls ( mean difference6SE: 4.5462.14), although the number of black women in the study was small. After adjustment for age, assay batch, month of blood draw, clinic and sample storage time, the odds ratio ( 95% confidence interval, CI) for lowest relative to highest quartile was 5.2 ( 95% CI 2.1, 12.8) for white cases and controls. The association in white women was stronger in women above the median age of 54 than in younger women, 4.7 ( 95% CI 2.1, 10.2) vs. 1.5 ( 95% CI 0.7, 3.0). There were no case- control differences in 25- D levels in either group. Conclusions: These data are consistent with a protective effect of 1,25- D for breast cancer in white women.