A new study from France has shown that women who were exposed to a combination of sunlight and dietary vitamin D had up to a 45% reduced risk of contracting breast cancer (BC). The researchers noted that “high” dietary vitamin D by itself did not correlate to a reduced risk of BC, whereas sunlight exposure alone did correlate to a lowered risk.
This research should come as no surprise, since there is a miniscule amount of vitamin D in the typical diet. For instance, the typical 3 ½-oz piece of farmed salmon contains about 175 International Units (IU) of vitamin D; 8 oz. of fortified milk 100 IU; 8 oz. fortified orange juice 100 IU. The amounts typically derived from eggs, oils and margarine is negligible. It is now felt by many experts in the vitamin D field that 4,000-5,000 IU of vitamin D supplementation is necessary for optimal health, so it can be seen that trying to optimize breast health with the paltry 400-500 IU from diet is like trying to color the ocean red with a cup of tomato paste.
Conversely, 20 minutes full-body exposure to summer sunlight at noon can produce as much as 20,000 IU; so this study, showing that sunlight correlates far better to lowered BC risk than does dietary vitamin D, would be expected. However, most people are not actively seeking the sunlight and are not even close to producing the 20,000 IU mentioned. Therefore, in this French BC study, it was probably the combination of both sunlight-produced vitamin D and dietary vitamin D that sufficiently increased blood levels to a threshold that triggered vitamin D’s cancer protection mechanisms, which are numerous.
Other research—a double blind, placebo controlled interventional study—has shown that when vitamin D supplementation is over 1,100 IU daily, there is a profound correlation to a lowered risk (from 60-77%)of all cancers in women.
And as to sunlight per se, Dr. Esther John and colleagues conducted research on the sun-exposure habits of women and correlated those habits to the risk of developing BC. Those women who had the greatest exposure to sunlight were 65% less likely to develop BC.
After the Institute of Medicine (IOM) made their inanely low recommendations for vitamin D supplementation (600 IU daily for all ages), it is good to see that research belying that foolishness continues to surface. We must remember that sunlight exposure is the most natural way to produce vitamin D, and that if supplements are going to be used when sunlight is not available, a minimum of 2,000-4000 IU daily is necessary to optimize blood levels for best health.
 Engel P, Fagherazzi G, Mesrine S, Boutron-Ruault MC, Clavel-Chapelon F. Joint effects of dietary vitamin D and sun exposure on breast cancer risk: results from the French E3N cohort. Cancer Epidemiol Biomarkers Prev 2010 Dec 2. [Epub ahead of print]
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D and calcium supplementation reduces cancer risk: results of a randomized trial. Am J Clin Nutr 2007;85:1586 –91.  John, E. et al. Vitamin D and breast cancer risk: The HANES 1 epidemiologic follow-up study, 1971-1975 to 1992. Cancer Epidemiology Biomarkers and Prevention 1999;8:399-406.