Q: What is Vitamin D and what does it do?

A: Vitamin D is a fat soluble vitamin known to play a major role in calcium absorption. More recently, it has been shown to have various other effects outside calcium regulation.

Q: What foods provide Vitamin D?

A: There are two forms of Vitamin D: D2 and D3. Vitamin D2 is found in plants and can be ingested in fortified foods or as a supplement. Vitamin D3 is made in the skin or can be ingested as oily fish, fortified foods or a supplement.

Q: How do you know if you're getting enough Vitamin D?

A: Vitamin D deficiency is defined as hydroxyvitamin D level of less than 20 nanograms per milliliter or ng/mL. A level less than 10 ng/mL is defined as severe deficiency. The optimal concentration of Vitamin D should be greater than 30 ng/mL. The Third National Health and Nutrition Examination Survey (NHANES III) has reported 25 to 57 percent of adults are Vitamin D deficient. One of the reasons for this is increased effort to avoid sun exposure and an increase in indoor lifestyle.

Q: Can you get Vitamin D from the sun?

A: Yes. However, sunscreen with SPF 15 blocks 99 percent of Vitamin D production in the skin. In the winter months, the deficiency worsens due to decrease in sunlight exposure.

Q: What are the effects of Vitamin D on health?

A: Vitamin D may play a role in the development of Type 1 and Type 2 diabetes. There have been a number of studies suggesting Vitamin D deficiency may increase the risk of development of Type 1 diabetes. Epidemiological studies have suggested Vitamin D replete people have a 33 percent decrease chance of developing Type 2 diabetes compared to Vitamin D deficient people. There is good evidence showing Vitamin D is involved in insulin secretion and is essential for insulin release. People with Vitamin D deficiency may be at risk not only for diabetes but also for cardiovascular disease. NHANES III has shown Vitamin D levels are inversely correlated with hypertension, diabetes, hypertriglyceridemia and obesity. In the Framingham Offspring study, the rate of fatal or nonfatal heart attack, ischemia, stroke or heart failure was 53 percent to 80 percent higher in people with low Vitamin D levels.

Q: What are the symptoms of Vitamin D deficiency?

A: In general, one of the first manifestations of Vitamin D deficiency tends to be muscle aches and pains followed by muscle weakness. Increasing Vitamin D to levels greater than 30 ng/mL tends to improve the weakness and decreases the risk of falls. It may also improve muscle function, which in turn may lead to improvement of diabetes.

Q: What is the role of Vitamin D in osteoporosis?

A: Vitamin D deficiency does not really cause osteoporosis. It causes osteomalacia, a state where the bones are not mineralized by calcium and other minerals. This leads to soft bones and increases the risk of fractures. On a DEXA scan, osteoporosis and osteomalacia can not be differentiated so it becomes important to have a complete workup done by a physician who specializes in osteoporosis before starting treatment of osteoporosis. The complete workup should be done to make sure there are no other treatable diseases possibly causing osteoporosis.

Q: What is the recommended dosage of Vitamin D?

A: Replacement of Vitamin D should be based on the serum concentration of Vitamin D. At a minimum, daily intake as recommended by most experts should be between 800 and 2000 IU. A dose of 2000 IU of Vitamin D per day has been recognized as being safe by the FDA's nutritional guidelines.

People with Vitamin D deficiency may require much higher doses than the RDA (recommended daily allowance).

Dr. Bankim A. Bhatt specializes in endocrinology, diabetes and metabolism with St. Luke's University Hospital.