The Truth About Vitamin D (cont.)
Vitamin D is so important that your body makes it by itself -- but only after skin exposure to sufficient sunlight. This is a problem for people in northern climates. In the U.S., only people who live south of a line drawn from Los Angeles to Columbia, S.C., get enough sunlight for vitamin D production throughout the year.
Dark skin absorbs less sunlight, so people with dark skin do not get as much vitamin D from sun exposure as do light-skinned people. This is a particular problem for African-Americans in the northern U.S.
How can I get enough vitamin D?
Thirty minutes of sun exposure to the face, legs, or back -- without sunscreen -- at least twice a week should give you plenty of vitamin D.
But this much direct sun exposure might also expose you to potentially dangerous levels of cancer-causing UV radiation. And unless you live in the South or Southwest, you probably won't get enough sunlight during the winter months for your body to make enough vitamin D. The American Academy of Dermatology recommends against getting vitamin D from unprotected exposure to sunlight.
It's probably a better idea to get vitamin D from foods or from supplements.
Will a vitamin D test tell me if I need more vitamin D?
That depends on whom you ask. As part of your regular blood test, your doctor can order a test for 25-hydroxyvitamin D (25-OHD).
The problem is not with the test. The problem is how to interpret the results. An expert committee convened by the Institute of Medicine in November 2010 concluded that "the cut-point values used to define deficiency, or as some have suggested, 'insufficiency,' have not been established systematically using data from studies of good quality."
Even so, most experts agree that anyone with a 25-OHD level of less than 15 ng/mL or 37.5 nmol/L (depending on the units reported by a lab) needs more vitamin D. A 2002 study found that 42% of African-American women of childbearing age had vitamin D levels below 15 ng/mL.
The IOM committee says that people are at risk of vitamin D deficiency at 25-OHD levels below 30 nmol/L (12 ng/mL), and that some people -- but not everyone -- may be at risk of vitamin D deficiency at 25-OHD levels from 30 nmol/L up to 50 nmol/L (12-20 ng/mL).
The Vitamin D Council considers the ideal 25-OHD level to be between 40 ng/mL and 70 ng/mL. But the IOM says there is no evidence of increased benefit at levels above 30 ng/mL, and that "there may be reason for concern" at levels above 50 ng/mL.
"There is a critical public health and clinical practice need for consensus cut-points for serum 25-OHD," the IOM committee states.
Which foods contain vitamin D?
Surprisingly few foods contain vitamin D -- unless it's added to the food. That's because your body is built to get vitamin D through your skin (from sunlight) rather than through your mouth (by food). But once your body has enough, it doesn't matter whether you got it through your skin or through your stomach.
There are three vitamin D super foods:
Other food sources of vitamin D include:
Nearly all milk in the U.S. is fortified with vitamin D. So are many brands of orange juice, yogurt, margarine, and ready-to-eat breakfast cereals.
How much vitamin D do I need?
In November 2010, the Institute of Medicine's expert committee set a new "dietary reference intake" for vitamin D.
Assuming that a person gets virtually no vitamin D from sunshine -- and that this person gets adequate amounts of calcium -- the IOM committee recommends getting the following amounts of vitamin D from diet or supplements (Note that the IOM's upper limit is not a recommended intake, but what the IOM considers the highest safe level):
That's not enough, says Boston University vitamin D expert Michael Holick, MD, PhD, professor of medicine, physiology, and biophysics, Boston University Medical Center. Holick recommends a dose of 1,000 IU a day of vitamin D for both infants and adults -- unless they're getting plenty of safe sun exposure.
In 2008, the American Academy of Pediatrics recommended that breastfed infants receive 400 IU of vitamin D every day until they are weaned. This doubled the AAP's previous recommendation.
The AAP also recommends 400 IU/day of vitamin D for children and teens who drink less than a quart of vitamin D-fortified milk per day.
The Vitamin D Council recommends that healthy adults take 2,000 IU of vitamin D daily -- more if they get little or no sun exposure.
There's evidence that people with a lot of body fat need more vitamin D than lean people.
But it's clear that the IOM's conservative recommendations will stir debate in the scientific and medical communities. Here's a rule of thumb: If you're considering taking more vitamin D than the IOM committee recommends, first check with your doctor or pediatrician.
Can I get too much vitamin D?