Abstract
B205
Background: Vitamin D is a hormone that regulates bone development, metabolism, cell growth and calcium homeostasis. Main sources of vitamin D include exposure to sunlight, fortified milk, certain types of fish, and vitamin D-containing supplements. There is accumulating evidence to suggest that vitamin D may be associated with reduced risks for several types of cancer including colon, prostate, and breast. We examined the relationship between vitamin D-related questions administered in a telephone interview questionnaire and circulating levels of 25-hydroxyvitamin D (25(OH)D). Methods : The relationship between vitamin D and breast cancer was investigated in a population-based case-control study. Validation of serum 25(OH)D for 203 of the 1135 randomly selected controls was conducted. The association between 25(OH)D and variables in a summer and winter telephone interview questionnaire was assessed. Questions pertaining to sun exposure and dietary sources of vitamin D over the previous month were asked alongside potentially confounding variables. Multivariate linear regression was used to assess these associations in the summer and winter. Results : Both models were adjusted for age, body mass index and skin colour. Overall sun exposure (number of days when more than half an hour was spent outdoors per week) ('7 days' vs. '<7 days' beta=11.01; p=0.01), coverage of arms and legs ('no' beta= 23.87 and 'partial' beta= 7.05 vs. 'yes'; p=0.0001) and milk consumption (beta= 1.10, p=0.001) best predicted 25(OH)D levels in the summer. Vitamin D-containing supplement use was marginally associated ('high' beta= 7.40 and 'moderate' beta= 10.45 vs. 'none'; p=0.07). The summer model explained 29% of the variance in serum 25(OH)D. The best predictors in the winter were sunlamp use ('no' beta= -28.21 vs. 'yes'; p=0.01), milk consumption (beta= 0.81; p=0.007) and vitamin D-containing supplements ('high' beta= 17.52 and 'moderate' beta= 13.43 vs. 'none'; p=0.0007). The winter model accounted for 21% of the variation in serum 25(OH)D. Interpretation : Sun exposure-related questions were strongly associated with 25(OH)D in the summer. Although relatively few people reported sun lamp use, an association with 25(OH)D was still found. Milk consumption was associated in both seasons, but vitamin D from supplements was more relevant in the winter. Overall there was evidence to suggest that questions designed to assess vitamin D exposure were in fact related to serum 25(OH)D. Conclusion : Based on the key predictor variables found in these models, targeted preventive interventions to modify vitamin D status can be sought if vitamin D is confirmed to have a protective role in breast cancer risk.
[Fifth AACR International Conference on Frontiers in Cancer Prevention Research, Nov 12-15, 2006]