Dietary Vitamin D and Calcium Intake and Premenopausal Breast Cancer Risk in a German Case-Control Study

Abstract

Epidemiological studies and laboratory data suggest that vitamin D may protect against the development of cancer, including breast cancer. Vitamin D supply affects the bioavailability of dietary calcium, which might also have anticarcinogenic effects. However, few studies considered them jointly. We used a population-based case-control study in Germany to examine the independent and joint effects of dietary vitamin D and calcium on premenopausal breast cancer risk. Dietary information was assessed using a validated food frequency questionnaire from 278 premenopausal cases and 666 age-matched controls. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated using multivariate models adjusting vitamin D models for calcium intake and vice versa. Breast cancer risk was significantly inversely associated with vitamin D intake. The OR and 95% CI for the highest intake category (≥ 5 μ g/day) was 0.50 (95% CI = 0.26–0.96) compared with the lowest (< 2 μ g/day; P_trend = 0.02). Dietary calcium intake was not associated with breast cancer (OR = 0.73, 95% CI = 0.41–1.29) for the highest (≥ 1,300 mg/day) versus the lowest category (< 700 mg/day), P_trend = 0.29). No statistically significant interaction between the 2 nutrients was observed. Our data support a protective effect of dietary vitamin D on premenopausal breast cancer risk independent of dietary calcium intake.

Acknowledgments and Notes

We are grateful to all participants for their help and patience as well as to the many gynecologists and oncologists in the clinics of the study regions for allowing us to contact their patients. We also thank U. Eilber for data coordination and management and D. Zoller for calculating dietary intake data. The epidemiological study was supported by the Deutsche Krebshilfe e. V. (Project number 70492). S. Abbas has a scholarship from the Deutsche Forschungsgemeinschaft, Graduiertenkolleg 793.

Notes

a: χ 2-Test.

b: Abbreviation is as follows: MET, metabolic equivalents. Data available for 187 cases and 525 controls.

c: Data on estrogen receptor and progesterone receptor status was available for 222 and 218 cases, respectively.

a: Wilcoxon rank-sum test.

a: Adjusted for number of births, first-degree family history, age at menarche, duration of breast feeding, body mass index, alcohol consumption, nonalcohol energy intake, and mineral and vitamin supplements; additional adjustment for calcium models only: vitamin D intake; for vitamin D models only: calcium intake. Abbreviation is as follows: CI, confidence interval.

b: For the fully adjusted model.

a: Low and high levels refer to below and above the intake recommendation of 5 μ g/day and 1,000 mg/day for vitamin D and calcium, respectively. Abbreviation is as follows: CI, confidence interval.

b: Adjusted for number of births, first-degree family history, age at menarche, duration of breast feeding, body mass index, alcohol consumption, nonalcohol energy intake, and mineral and vitamin supplements.