Vitamin D deficiency common in Americans? Known as the "sunshine vitamin," vitamin D is produced by the body in response to sunlight. But with this year's winter weather, many of us are spending even more time indoors — and when we do go out, we're bundling up.
What causes vitamin D deficiency? The main causes of vitamin D deficiency are a diet low in vitamin D and infrequent (or blocked) exposure to sunlight. There are genetic disorders that can cause an inability for the body to absorb vitamin D, but these diseases are rare.
In the United States, a large percentage of the population is deficient in vitamin D, mainly due to overall poor diets. Also, many skin lotions and make-up have sunscreens in them, limiting our body's ability to produce vitamin D following sunlight exposure.
What health problems can occur due to vitamin D deficiency? Vitamin D reduces risk of chronic and infectious diseases, including many types of cancer, autoimmune diseases, and certain bacterial infections. This vitamin promotes good vascular health, which can lower risk of heart disease and stroke. Vitamin D may promote good insulin regulation, consistent with lower risk of type 2 diabetes. Consequently, vitamin D deficiency conceivably may increase risk of these disorders, though more studies are needed to confirm.
Vitamin D deficiency has been linked to an elevated risk of Alzheimer's disease. Studies performed in my laboratory at the University of Kentucky showed that rats who were fed a low vitamin D diet had elevated measures of free radical damage to their brains compared to counterparts who were fed a normal or high vitamin D diet. The rats also showed significant deficits in learning and memory.
How can I make sure to get enough vitamin D? Each person should consult a physician for the best advice specific to the individual on how to increase vitamin D. In my opinion, the two easiest ways to elevate vitamin D levels are eating a diet rich in Vitamin D and take a daily supplement.
Vitamin D is rich in certain fish, including salmon and halibut. Green, leafy vegetables also contain high levels of vitamin D. In the United States, milk is fortified with vitamin D as are other foods.
Exposure to sunlight for as little as 15 minutes a day will produce sufficient daily vitamin D. Of course, there are caveats to sun exposure, including being careful to avoid too much exposure.
Allan Butterfield is the Alumni Association Endowed Professor of Biological Chemistry at the University of Kentucky.