Much has been written recently regarding the health benefits of vitamin D3 supplementation. Unfortunately it is difficult to find reliable research to support these claims. Vitamin D is a fat-soluble vitamin that is essential for calcium absorption and regulation. Through its effects on calcium, it plays important roles in bone, nerve, muscle, and immune system functions. Vitamin D has long been recognized as essential for calcium absorption and the prevention of osteoporosis. More recent claims have been made that vitamin D may also play important roles in reducing muscle and nerve pain and improving respiratory tract health.

Vitamin D3 (cholecalciferol) is produced in the skin when exposed to ultraviolet light, found in some foods, and available as supplements. Vitamin D3 is inactive. It must undergo two hydroxylations to become active and useful to the body. The first occurs in the liver where it is converted to calcidiol. The second occurs in the kidney to become calcitriol which is the physiologically active form.

Nutrient recommendations are established by the Food and Nutrition Board (FNB) at the Institute of Medicine of The National Academies. The Recommended Daily Allowance (RDA) is the average daily intake sufficient to meet the nutrient requirements of 97-98% of healthy people. The Adequate Intake (AI) is used when there is not enough evidence to establish an RDA. It is set at a level assumed to ensure adequate levels in the body. The Tolerable Upper Level (TUL) is the maximum daily intake unlikely to cause adverse health effects. The AI for vitamin D has been established at 200 IU/day from birth to 50 years old, 400 IU/day from 51 to 70 years, and 600 IU/day at 71 years and older. These recommended amounts have been criticized by researchers as inadequately low.

Recently published reports found an inverse relationship between vitamin D blood levels and respiratory tract infections, including influenza (flu) and pneumonia. In other words, low vitamin D levels were associated with higher rates of respiratory tract infections. More research is needed to determine if vitamin D levels may be a cause of increased risk of respiratory tract infections. Some researchers are calling for studies to be conducted to determine if vitamin D supplementation should be used to prevent and treat flu.

Some practitioners are recommending that 2,000 IU/day of vitamin D3 be taken to improve overall health. Vitamin D supplementation has been reported to reduce osteoporosis, reduce back pain, decrease the risk of cancers (especially colorectal cancer), and reduce the risk of respiratory tract infections, including the flu. Patients should talk to their doctors before taking nutritional supplements. Blood tests may be needed to determine existing vitamin D and calcium levels before starting supplementation because in a very small percentage of patients vitamin D supplementation can raise calcium to dangerously high levels. This seems to occur more frequently in African Americans.

References: http://ods.od.nih.gov/factsheets/vitamind.asp, http://www.vrp.com/articles.aspx?ProdID=2130, http://en.wikipedia.org/wiki/Vitamin_D_and_influenza, http://www.medicalnewstoday.com/articles/168587.php.

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