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Report: Most Americans Don't Get Enough Vitamin D

Three out of every four Americans are deficient in vitamin D. That's a big increase, according to a study published in the Archives of Internal Medicine.

Transcript

STEVE INSKEEP, host:

Consider this when planning your breakfast this morning. Three out of every four Americans are deficient in vitamin D. That's a big increase, according to a study published in the Archives of Internal Medicine. Here's NPR's Patti Neighmond.

PATTI NEIGHMOND: Vitamin D helps build strong bones. This we know. It helps the body absorb calcium. But over the past 10 years, scientists have discovered it has lots of other potential health benefits, too. Dr. Adit Ginde says advances in molecular genetics have taught us a lot.

Dr. ADIT GINDE: Vitamin D is involved in the regulation of over 1,000 human genes. It appears to be necessary for some normal function. So for instance, for heart disease, there are receptors for vitamin D in the blood vessels, and it appears to play a roll in prevention of hardening of the arteries or stiffness of the arteries, which can play a roll in blood pressure and even the development of cardiovascular disease.

NEIGHMOND: It's been known for years that severe deficiencies of vitamin D can lead to rickets, where bones don't develop properly. But Ginde says vitamin D also seems to be important in regulating the immune system. People with milder deficiencies tend to get more respiratory infections. And the vitamin may even have a role in preventing some cancers.

So to find out whether Americans were getting enough vitamin D, Dr. Ginde and colleagues from the University of Colorado Denver School of Medicine analyzed data from national health surveys. Ginde found that 20 years ago, a little more than half of those surveyed were getting less than the optimal dose. But more recently…

Dr. GINDE: Over three out of every four Americans now have levels below what we believe is necessary for optimal health.

NEIGHMOND: UV rays from the sun do interact with the skin to produce vitamin D in the body, but it's hard to get enough that way, especially now, with people so aware that it's important to wear sunscreen and hats in order to avoid skin cancer. To get around that, Ginde thinks most adults should take vitamin D supplements. For decades, the recommended daily allowance has been 200 to 600 international units a day, depending on your age.

Dr. GINDE: Most people could use more vitamin D than that current recommendation. We're still learning about - sort of what the optimum dose is to recommend. But probably, it's going to end up being at least 1,000 international units per day.

NEIGHMOND: But the Institute of Medicine committee that sets the RDAs for vitamins is not yet convinced. They are currently evaluating all the data on vitamin D, and expect to make a new recommendation within a year or so. Whatever their decision, nutritionist Bruce Hollis with the Medical University of South Carolina says that without supplements, vitamin D deficiencies are likely to get worse - especially with America's expanding waistline.

Dr. BRUCE HOLLIS (Medical University of South Carolina): We know that obesity and increased BMI causes vitamin D to somehow disappear from the blood. And it takes a lot more - either sun exposure or intake to overcome it. We don't exactly know the mechanism, but we do know it's a fact. So people who are extremely obese usually have very poor vitamin D status.

NEIGHMOND: In the study, Dr. Ginde found that people with darker skin - African Americans and Hispanics - had even lower levels of vitamin D than Caucasians. That's because the skin pigment melanin blocks UV radiation, which can be protective against sun damage but also means less vitamin D. That's why Ginde and Hollis say people of color might benefit even more than whites from vitamin D supplements.

Patti Neighmond, NPR News. Transcript provided by NPR, Copyright NPR.

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