Vitamin D levels: sufficient for winter? By Marc Sorenson, EdD
Vitamin D levels and sunshine are exceptionally important to human health, and therefore we should be aware of vitamin D science. The Vitamin D Society of Canada is always at the forefront of the research on vitamin D levels and sunlight. And, they deliver press releases to keep people from Canada (and the world) apprised of new and important findings. Hence, I would like to comment on the salient points of their latest release. As I do so, it is especially relevant to note that vitamin D levels are surrogate measures for sun exposure.
The relationship of vitamin D to sun exposure
Ninety percent of vitamin D levels in the blood is due to sun exposure. The UVB portion of sunlight stimulates vitamin D production in skin. Therefore, a UVB light source, which produces vitamin D levels, is the best source in winter. Remember also that the press release information is true for the world, not just Canada.
Salient points about vitamin D levels and sunlight: breast cancer
- First of all, consider a breast-cancer study published in the scientific journal, Plos One. It showed that women with the highest vitamin D levels had a reduced breast-cancer risk. Most noteworthy, women with levels > 60 ng/ml had 82% reduced risk, compared to those with levels < 20 ng/ml. Furthermore, there was a dose-response decrease. For each increase in vitamin D levels, there was a concomitant decrease is breast-cancer risk.
Vitamin D levels and Breast Cancer
- Since we mentioned that vitamin D is produced by sun exposure, we should mention an Iranian sunlight-breast cancer study. In Iran, among women who totally avoid sun exposure, there is a 10-fold increase breast cancer risk. That is an especially relevant fact for women who believe they should avoid the sun! And remember, melanoma is also reduced in those who are regularly exposed to sunlight.
Another Vitamin D levels- and sunlight-deficiency cancer
- It seems like if breast cancer is reduced by high vitamin D levels, the same relationship could exist for other cancers. Hence, the press release mentioned colorectal cancer as the second disease associated to low vitamin D levels or low sun exposure. And, it mentioned another important piece of research. Participants with vitamin D levels below 12 ng/ml had a 31% higher risk of colorectal cancer. Those with levels above 30 ng/ml had a 27% reduced risk.
Other disorders associated with vitamin D levels
In addition, the press release mentions four other disorders where higher vitamin D levels reduce risk or improve the condition. The disorders: diabetes (81% reduced risk), multiple sclerosis (45% reduced risk), preterm birth (62% reduced risk) and poor cognitive function. As to cognitive function, those who spent the most time outdoors with the least sun protection, had better cognitive function.
Finally, this is an excellent press release regarding vitamin D levels and sunlight. I strongly suggest you read it. http://www.vitamindsociety.org/press_release.php?id=60 Also, see the previous blog regarding the vitamin D Society and vitamin D levels: https://sunlightinstitute.org/vitamin-d-canada-warning/
 Reichrath J. The challenge resulting from positive and negative effects of sun: how much solar UV exposure is appropriate to balance between risks of vitamin D deficiency and skin cancer? Prog Biophys Mol Biol 2006;92(1):9-16
 McDonnell SL, Baggerly CA, French CB, Baggerly LL, Garland CF, Gorham ED, Hollis BW, Trump DL, Lappe JM. Breast cancer risk markedly lower with serum 25-hydroxyvitamin D concentrations ≥60 vs <20 ng/ml (150 vs 50 nmol/L): Pooled analysis of two randomized trials and a prospective cohort. PLoS One. 2018 Jun 15;13(6).
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 McCullough ML, Zoltick ES, Weinstein SJ, Fedirko V, Wang M, et al. Circulating Vitamin D and Colorectal Cancer Risk: An International Pooling Project of 17 Cohorts. J Natl Cancer Inst. 2018 Jun 14.