Plasma 25-hydroxyvitamin D and premenopausal breast cancer risk in a German case-control study

Laboratory and epidemiological data have linked vitamin D to breast cancer prevention. Beside dietary intake, endogenous production of vitamin D substantially contributes to a subject's vitamin 1) status. Most studies, however, have assessed dietary intake only. Although differential effects of vitamin D on premenopausal and postmenopausal breast cancer have been discussed, this is the first study to investigate the association of plasma 25-hydroxyvitamin D [25(OH)D], as indicator of the overall vitamin D status, with breast cancer risk with restriction to premenopausal women only. We used data of a population-based case-control study comprising 289 cases and 595 matched controls. Information on socio-demographic and breast cancer risk factors was collected by questionnaire and plasma 25(OH)D was measured by enzyme immunoassay. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated using conditional logistic regression. We observed a significant inverse association between breast cancer risk and plasma 25(OH)D concentrations. Compared with the lowest category (<30 nmol/L), the ORs (95% CI) for the upper categories (30-45, 45-60, >= 60 nmol/L) were 0.68 (0.43-1.07), 0.59 (0.37-0.94) and 0.45 (0.29-0.70), respectively (p(trend) = 0.0006). The association was shown to be nonlinear (p(nonlinearity) = 0.06) in fractional polynomial analysis with a stronger effect in women at low plasma 25(OH)I) levels, providing some evidence of a threshold effect (at circa 50 nmol/L). The association was stronger in progesterone receptor negative tumors, with suggestive evidence of effect heterogeneity (p(heterogeneity) = 0.05, case-only model). Our findings support a protective effect of vitamin D for premenopausal breast cancer. (C) 2008 Wiley-Liss, Inc.