Vitamin D and Its Health Benefits

Vitamin D is a fat-soluble vitamin that helps the body absorb and regulate calcium levels in the body.

It is critical for building and maintained bone mass which, in turn is critical to our health. The presence of vitamin D receptors in tissues throughout the body suggests that vitamin D has important roles beyond bone health. It can help reduce cancer cell growth as well as inflammation and infections. 

Insufficient vitamin D can even predispose to diabetes and hypertension.

Most of us need to take vitamin D supplements in order to have sufficient levels of the compound in our bodies, especially since most foods do not contain much vitamin D unless it is added (eg. to milk). 

The two forms are vitamin D2 (“ergocalciferol”) and vitamin D3 (“cholecalciferol”). Recent studies indicate that vitamin D3 is significantly more potent than vitamin D2. Both forms are produced in the skin if there is sufficient exposure to the sun’s ultraviolet-B (UVB) light. Most of us do not get enough sunlight exposure to generate the needed amount of vitamin D because we live in northern or southern latitudes, where the sun’s ray are indirect, or we are not outside with exposed skin very much. Those with darker skin have lots of melanin, which limits vitamin D synthesis. 

Accordingly, vitamin D deficiency may be the most widespread nutrient deficiency in developed countries.

When vitamin D is taken orally or produced in the skin is metabolized in the liver to a precursor of the hormone calcitriol, which is manufactured in the kidney. Calcitriol increases absorption of calcium in the gut. Vitamin D has recently beed found to have other essential roles in the body. For example, it increases (“upregulates”) responses to estrogen and progesterone. Immune cells called macrophages require vitamin D in order to synthesize proteins needed to attack bacterial pathogens. Low vitamin D levels are associated with an increase incidence of a variety of cancers as well as both type 1 and type 2 diabetes. The same applies to cardiovascular disease, especially hypertension.

As with other nutrient deficiencies, chronic oxidative stress and inflammation, low levels of vitamin D contribute to the diseases associated with aging. Fortunately, this can be easily remedied.

Recommendations for vitamin D intake are based only on bone health and are (variably) 400 IU/d for infants, 600 IU/d for adults, and 800 IU/d for those over age 70, since vitamin D synthesis in the skin decreases with age. We can have our vitamin D levels checked with a blood draw – healthy levels are over 30 ng/mL (75 nmol/L). 

The Institute of Medicine has suggested that the upper limit for supplementation is 4,000 IU/day. One reasonable approach would be to take 800-1,000 IU/day for a few months and then have a blood level checked to help determine dose adjustment. Toxicity of vitamin D, as with other fat-soluble vitamins, is reported, with symtpoms including anorexia, weight loss, cardiac rhythm disturbances, and hardening of arteris related to calcium deposition.

Note: Although I am a physician, the content in this article is not meant to diagnose, treat, cure or prevent illness or disease in the reader – it is for educational purposes only.

References

• Heaney R. Vitamin D in health and disease. Clin J Am Soc Nephrol. 2008;3(5):1535–1541.
• Feskanich D, Ma J, Fuchs CS, Kirkner GJ, et al. Plasma vitamin D metabolites and risk of colorectal cancer in women. Cancer Epidemiol Biomarkers Prev 2004;13:1501– 1508.
• Institute of Medicine, Food and Nutrition Board. National Academy Press, 2010.