Vitamin D is found in two forms: D2, which is synthesized in plants, and D3, which is synthesized in the skin upon the exposure of vitamin D2 to UV light. As little as 10 minutes of daily exposure to sunlight may be enough to prevent vitamin D deficiency. Keep in mind, sunscreen limits the amount of UV rays penetration, so you may need to spend more time in the sun to get the adequate supply of vitamin D3 when wearing sunscreen. The best dietary sources of vitamin D are dairy products (fortified), fish, and eggs.
After vitamin D is either consumed or synthesized in the body, it is transported to the liver where it is converted to calcidiol (25-hydroxyvitamin D). Calcidiol is then transported to the kidneys where it is converted into calcitriol (1,25-dihydroxyvitamin D), the most potent form of vitamin D. Because calcitriol exists in the blood for only a short period of time, vitamin D levels are generally measured by serum calcidiol levels.
A meta-analysis of observational studies performed in 2011 by the International Journal of Cancer reinforced claims that vitamin D deficiency is associated with an increased risk of certain types of cancers, specifically colorectal cancer. According to the study, there is an inverse relationship between 25-hydroxyvitamin D levels and risk of colorectal cancer. When all of the studies were pooled, an increase of 10 ng/ml of serum 25-hydroxyvitamin D was associated with a relative risk of .85 compared to standardized patients. This means those individuals with higher levels of vitamin D had a decrease in the risk of developing colorectal cancer by 15%. This study also examined the effect of vitamin D levels on prostate and breast cancer rates, but the analysis found no statistical association between them. (Gandini et. al, 2011)
Take home point: supplementing your diet with approximately 1000 IU of vitamin D3 (cholecalciferol), especially in the winter months when you spend less time in the sun, may help to decrease your risk of various diseases including: colorectal cancer, hypertension, dementia, cardiovascular disease, and certain autoimmune diseases*.
Gandini et. al. Meta-analysis of observational studies of serum 25-hydroxyvitamin D levels and colorectal, breast and prostate cancer and colorectal adenoma. Int. J. Cancer: 128, 1414-1424 (2011).
Natural Standards Database- Vitamin D
*This is not a diagnosis for taking this supplement. If you would like to discuss with a doctor if vitamin D supplementation would benefit you, please call the office at 724-934-7788.