Are You Getting Enough Vitamin D?
Many of us are short on Vitamin D, which has plenty of health benefits.
By Kathleen Zelman, MPH, RD/LD
Reviewed by Brunilda Nazario, MD
It has long been known as the vitamin that cured rickets. But today, vitamin D is being hailed for being able to do much more than that.
Scientists have known for some time about vitamin D's role in helping the body absorb calcium, in maintaining bone density, and in preventing osteoporosis. But new research suggests it may also help protect against chronic diseases such as cancer, type 1 diabetes, rheumatoid arthritis, multiple sclerosis, and autoimmune diseases.
Yet many adults have low blood levels of vitamin D. Vitamin D is not abundant in our usual food choices, so we get most of the vitamin from sun exposure and multivitamins. The problem is that the sun is not a reliable source for everyone.
The season, time of day, geography, latitude, level of air pollution, color of your skin, and your age all affect your skin's ability to produce vitamin D. Further, the form of Vitamin D found in most multivitamins is vitamin D2, which does not deliver the same amount of the vitamin to the body as the more desirable D3 form.
Deficient in D?
Vitamin D is the only vitamin that is also a hormone. After Vitamin D is made by the skin or eaten, the kidney and liver help to convert it into an active hormone form. As a hormone, it controls calcium absorption to help the body build strong bones and teeth, and it helps maintain muscle strength. When you are deficient in calcium and vitamin D, your bones break down to supply calcium to the rest of your body. But being deficient in vitamin D can take a toll on more than just your skeleton.
"There have been concerns about vitamin D status in the U.S. because of increasing reports of deficiencies, with an estimated 10 million Americans over age 50 diagnosed with osteoporosis," says Atlanta-based rheumatologist Eduardo Baetti, MD.
"Vitamin D deficiency is associated with low bone mass and osteoporosis because vitamin D is needed to absorb calcium from the diet. Low levels of vitamin D have also been linked with poor muscle strength and other chronic conditions, such as autoimmune disease and some forms of cancer."
The Sunshine Vitamin
D is also the only vitamin that does not need to be consumed in food or supplements because our bodies are efficient at making it when our skin is exposed to direct sunlight (not through a window). But not all sun exposure is the same, and many factors help determine how much we absorb. In general, the further away you are from the equator, the more efficient the vitamin D production, but cloud cover and air pollution can hinder the sun's ultraviolet (UV) rays.
Many people living in the Southern United States can get enough vitamin D by getting about 10-15 minutes of sun exposure on their arms and face a few times a week -- as long as they don't use sunscreen, which blocks some of the UV rays necessary to make the vitamin.
Along with geography, age and skin pigmentation are also factors.
Even in Atlanta, where the sunshine is adequate all year long, Baetti says, many of his patients -- especially elderly and dark-skinned people -- have low levels of vitamin D.
Dark pigment in the skin reduces the skin's ability to synthesize vitamin D from sunlight by 95%.
"Darker skinned people need 5-10 times as much exposure to synthesize the same amount of vitamin D as lighter skinned people," says vitamin D expert Michael Holick, PhD, MD.
But what about the dangers of sun exposure, which dermatologists often warn us about?
How Much Do We Need?
The current recommended intake of vitamin D is 200 IUs (international units) for those up to age 50; 400 IUs for people 51-70; and 600 IUs for those older than 70. Requirements increase with age because older skin produces less vitamin D.
But these recommendations date back to 1997. "Additional studies have been published since that time documenting the effectiveness of higher levels of vitamin D," says Holick, who was a member of the Institute of Medicine (IOM) committee that issued the recommendations.