Adequate sun exposure plus vitamin D supplementation could reduce the risk of breast cancer, says a French study.
The meta-analysis of ten trials with data from 67,721 postmenopausal women collected over 10 years indicated that women living in sunny climes combined with high dietary or supplemental intakes of vitamin D were at a significantly reduced risk of breast cancer compared to women with high sun exposure and low intakes of the vitamin (1). The risk of breast cancer for women residing in regions with the highest average daily UV exposure (living below a latitude of 46°North) combined with high dietary vitamin D intakes was 32% lower. With high UV exposure and high supplemental intakes the risk was reduced by 45%. No associations were observed for dietary and supplemental intakes of vitamin D alone.
The researchers commented that although these results do not support a linear dose-response relationship of UV radiation dose and dietary vitamin D on breast cancer risk, the findings suggest that a threshold vitamin D exposure is required to prevent breast cancer. This minimal amount is likely to vary with individual ability to metabolize or synthesize vitamin D from both sources. The scientists concluded that in view of the low mean vitamin D dietary intake in France, with 25(OH) vitamin D serum concentrations mostly below the 30 ng/mL recommended threshold, the results suggest that an increase in overall vitamin D intake should be encouraged by food and health agencies, possibly through fortification of foods.
Numerous studies have suggested associations between high vitamin D (25OHD) blood levels and lower risks of certain cancers. However, the relationship between vitamin D and breast cancer is still ambiguous, which may be related to a combination of dietary, supplemental and sunlight exposure as the source of raising vitamin D levels. Experts commented that further in-depth analyses – especially measuring 25(OH)D repeatedly at different time points before diagnosis – are highly desirable to enable more precise estimates and a better understanding of the role of vitamin D in breast cancer development and prevention.