Vitamin D and Cancer

Vitamin D and breast cancer

SAN DIEGO, CA.

A report has just appeared in the Journal of Steroid Biochemistry & Molecular Biology by Garland et al that addresses the issue of vitamin D and breast cancer risk with a pooled analysis of studies that determined the vitamin D status from serum 25-hydroxyvitamin D (25(OH)D) levels. The list of authors includes both well-known vitamin D experts and nutritional epidemiologists. The authors were only able to find two studies that met their requirements for inclusion in their pooled analysis, but together they involved 1760 individuals. Both studies covered a wide range of 25(OH)D levels and exhibited a high level of inverse correlation between breast cancer risk and the serum level of this vitamin D marker. When pooled analysis was carried out, the odds ratios for the lowest to highest quintile of 25(OH)D levels were 1.00, 0.90, 0.70, 0.70 and 0.50, i.e. the highest vitamin D status provided a 50% reduction in risk. The authors present a graph of risk (odds ratio) against serum 25(OH)D levels with an amazing correlation coefficient of 0.94 (a statistical measure of the goodness of fit to the model, in this case a straight line, and 1.00 represents a perfect fit), a correlation coefficient that would please those trained in the physical sciences and in fact a correlation very rarely seen in plots presented in the medical literature.
The authors discuss the level of intake that would accomplish the 50% level of risk reduction. If a person were to start at a serum level of 24 nmol/L (10 ng/mL) it would require supplementation of 4000 IU/day to achieve the required level of 120 nmol/L. This exceeds the current upper limit of 2000 IU/day. However, as they point out, a proposal has been made to raise this limit to 4000 IU/day. Levels of 24 nmol/L are not uncommon among US women in the winter months. An alternative they explore is to take 2000 IU/day orally and make up the balance by judicious sun exposure. They estimate that 12 minutes of sun exposure for 50% of the skin would produce the missing 2000 IU. However, this would not happen in the northern latitudes in the winter months. The authors hammer home their point regarding the importance of vitamin D by calculating that, based on their data, an intake of 4000 IU of vitamin D per day would, in the U.S., prevent over 100,000 cases of breast cancer per year. Intake of 2000 IU/day was estimated to prevent 66,000 cases. In this paper, vitamin D refers to vitamin D3. Garland, C. F. et al. Vitamin D and the Prevention of Breast Cancer; Pooled Analysis. Journal of Steroid Biochemistry & Molecular Biology, 2007, Vol. 103, pp. 708-711.