I recently read a great review article on the new recommendations for Vitamin D intake in the March 2011 issue of “Contemporary Pediatrics”. I thought I would use this article to answer some question about this essential vitamin.
What is Vitamin D?
Vitamin D is a fat soluble vitamin. It’s precursor, 7-dehydrocholesterol, is synthesized from the cholesterol molecule. When sunlight hits this molecule in the skin it is converted into Vitamin D3. It is converted further in the liver and then in the kidney to its final active form. Because of increased awareness of the risk of skin cancer and use of sunscreens we are more dependent on food sources of Vitamin D.
What are the sources of Vitamin D?
Vitamin D is found naturally in a few foods like oily fish and egg yolks. Many foods are now enriched with Vitamin D, like milk, cereal and some orange juices. See the NIH website for some selected food sources of Vitamin D.
What does Vitamin D do?
Most of what is known about the function of vitamin D is related to regulation of calcium, by increasing absorption of calcium by the intestine and increasing bone mineralization. It has also been found that there are receptors for Vitamin D in many other cells including immune cells and skin cells.
What happens when children don’t get enough Vitamin D?
In a vitamin D deficient state, absorption of calcium by the gut is significantly impaired. Low calcium can lead to decreased mineralization of bone, or osteomalacia. When this happens in young bones with open growth plates, it is called rickets. With rickets the cartilaginous growth plates become disorganized and abnormal appearing on Xrays. By supplementing with Vitamin D this condition can be reversed in a matter of a few weeks. Although the Institute of Medicine could not support a causal relationships, Vitamin D deficiency is also associated with cardiovascular disease and type 2 diabetes.
How much Vitamin D do you need per day?
The Institute of Medicine issued a report in 2011 which updates guidelines for Vitamin D intake. In their report they stated that for babies age 0-6 months the daily requirement for Vitamin D is 400 IU per day. For babies over 6 months, children, and adults the daily requirement is 600 IU per day. See my post on calcium for information on calcium requirements.
Who is at risk for Vitamin D deficiency?
People who are dark skinned, live in northern latitudes with less sun exposure, people who take medicines like antiepileptic drugs (which increased metabolism of Vitamin D), people who are on chronic steroid therapy, and people who have intestinal malabsorption from diseases like cyctic fibrosis and inflammatory bowel disease are all at risk for Vitamin D deficiency. Breastmilk is naturally low in Vitamin D, even when women take supplements. The range can be anywhere from less than 25 IU/liter to 78 IU per liter. Therefore, infants who are exclusively or mostly breastfed are at risk for Vitamin D deficiency and rickets. If you are breastfeeding your baby, talk to your pediatrician about vitamin D supplementation shortly after birth.
How do you know if you have Vitamin D deficiency?
If you have the risk factors for Vitamin D deficiency your doctor may elect to do a simple blood test to check your Vitamin D level. There is some debate on what the cutoff levels should be for vitamin D insufficiency and deficiency, but it is now believed that the normal range is between 20-50 ng/ml for all ages.
How is Vitamin D deficiency treated?
With the guidance of a physician somewhat higher doses of Vitamin D can be prescribed over 2-3 months, or superhigh doses can be prescribed for a much shorter period. After vitamin D levels return to normal, the recommended daily dose of Vitamin D can be resumed. Vitamin D deficiency should be treated with the help of a physician, as too high levels of vitamin D in the blood can lead to a high blood level of calcium, causing potentially dangerous side effects.