Letter From Director
July 2010
Vitamin D a hot topic
Being nicknamed the “Sunshine Vitamin” was not the only reason that made vitamin D a hot topic. It has also been well known for its role in bone metabolism. But the important role of vitamin D beyond that was the discovery of the 1,25 dihydroxyvitamin D nuclear receptor in most tissue. This increased interest in vitamin D has come about with recently introduced evidence that vitamin D can regulate the immune system and thereby it is implicated in several immune-mediated disease states. Several studies have linked vitamin D levels with different clinical outcomes like incidence of cancer, increase risk of tuberculosis, periodontal disease, reduced muscle tone and lower-extrimity function, diabetes, and autoimmune disorders and according to a study published in the Journal of Neurology, Neurosurgery, and Psychiatry vitamin D may have an important role in keeping the brain in good working order in later life. The recognition of vitamin D deficiency in so many conditions has resulted in an increased volume of testing for vitamin D within the past 2 years at the rate of 80-90% increase per year.
Sunlight is the best source of vitamin D production, it helps synthesizing vitamin D from its precursor. Then vitamin D is converted to 25 hydroxy (OH) vitamin D by the liver which in turn is converted to 1,25 dihydroxyvitamin D by the kidney. 25 OH vitamin D is the major form of the hormone found in the blood, and because of its long half-life and higher concentration 25 OH vitamin D is commonly measured to assess and monitor vitamin D status in individuals. It is available in 2 forms: D2 which is obtained from vegetable sources, and D3 which is derived from exogenous (animal diet) and endogenous sources (from cholesterol after exposure to sun).
The optimal levels have yet to be established, although serum 25 OH vitamin D levels of 30 ng/mL or greater are generally recognized as sufficient, some researchers believe that values of 40 to 60 ng/mL are more appropriate, while others suggest levels as high as 55 to 90 ng/mL are necessary to sufficiently prevent adverse health outcomes. In addition, several studies have shown that the serum concentration of 25 OH vitamin D needs to be at least 40 ng/mL to reduce fracture risk.
Vitamin D deficiency is more common than it was thought; with an estimated 50% of the elderly and 50% of the women at any age have inadequate level of vitamin D. Increased deficiency with age may be due to the limited exposure to the sun in elderly due to limited outdoor activity and the decrease in their ability to make vitamin D. Some of the recommendations to improve vitamin D status in elderly include: fortification of food, vitamin D supplements (and calcium) and, although exposure to sunshine is recommended, it is still controversial due to the risk of skin cancer and its limited effectiveness among the elderly.