Vitamin D may be the most important supplement you’re not taking—or not taking enough of. Most of us—and even our doctors—have little idea that taking regular amounts of it may help stave off some of the most common life-threatening illnesses.

Best known for building bones and preventing rickets—a bone disease more common in the days of Charles Dickens than today—vitamin D has recently been shown to lower the risk of diabetes, hypertension, multiple sclerosis, osteoporosis, memory loss and several types of cancer.

Despite this good news, most Americans don’t get near enough vitamin D. And among African Americans, some experts have called vitamin D deficiency a “hidden epidemic” and have speculated that low levels are to blame for higher rates of diseases such as hypertension, heart disease and diabetes. The Chicago Sun-Times went even further, linking African-American death rates from aggressive forms of breast and prostate cancer to low levels of vitamin D.

In the body, vitamin D is produced by sun exposure. But Americans aren’t exposed to as much sunlight as we used to be—either because we’re inside watching TV or hunched over computers or avoiding the sun to prevent skin cancer. 

So how much vitamin D do we need? That’s still being debated. In March, researchers at the University of Colorado Denver School of Medicine found that 3 in 4 Americans had insufficient levels of vitamin D, up from about 1 in 2, when measured 20 years ago.

Last fall, the American Academy of Pediatrics recommended infants, children and adolescents double the amount of D they ingest each day. The government recommends a daily intake of 200 international units (IU) from birth to age 50, 400 IU for people between 51 and 70, and 600 IU for those over 70.

Other experts have suggested even bigger boosts. The University of Colorado researchers advised increasing vitamin D intake to 1,000 IU daily. The well-respected Institute of Medicine went even further, recommending 2,000 IU a day. So drinking fortified milk, at 100 IU a glass, is just not enough.

New national guidelines are expected next year, and there’s little doubt that recommended vitamin D intake will be increased.  

To help sort through the vitamin D maze, we spoke to Dr. Consuelo Hopkins Wilkins, an assistant professor of medicine and psychiatry at Washington University School of Medicine in St. Louis, who has spent nearly a decade studying this overlooked vitamin.

The Root: How does exposure to sunlight produce vitamin D?
Dr. Consuelo Hopkins Wilkins: Everybody has the ability to make vitamin D. In the second layer of the skin, there’s a kind of a pre-vitamin D. When the skin is exposed to ultraviolet light, it activates this pre-vitamin D, which makes its way through the blood stream to the liver and kidney. There, it gets further activated from pre-vitamin D to vitamin D.

TR: What has caused our worsening problem of vitamin D deficiency?
CHW In general, people are exposed to the sun less, partly because of the risk of skin cancer. And we’re wearing more sunscreen, which blocks production of vitamin D. People are also living longer, and as we get older, we’re less likely to be in the sun. Aging also affects the skin’s ability to convert pre-vitamin D into vitamin D, and in older people, the liver and kidney can’t activate it as well.

Another contributing factor is that more and more people are overweight or obese. Research shows that when you expose overweight and normal weight people to the same amount of sun, the heavier group doesn’t produce as much vitamin D. No one is sure why, but it may be that vitamin D is “hiding” in fat cells.

TR: Why are African Americans particularly vulnerable to vitamin D deficiency?
CHW Melanin protects the skin against ultraviolet light. But by blocking the sun’s rays, melanin affects the skin’s ability to activate pre-vitamin D. So the darker the skin, the less vitamin D you produce. In the scientific literature, the difference is striking.

TR: How do you know if you have enough vitamin D in the body?
CHW Your doctor can give you a blood test. You probably have to ask for it, and here in St. Louis it costs about $90. There’s also a home test you can use, which costs about $65 [or] $75. Serum vitamin D is measured in nanograms. Ideally, your level should be over 30 ng/ml but less than 100. Too much vitamin D in the blood, which is rare, can lead to toxicity.

TR: How do you get more vitamin D?
CHW: Start with foods. Dairy products and some breads and cereals are fortified with vitamin D. Fatty fish, like sardines, salmon and mackerel is a good source. Liver and eggs are also good sources. Cod liver oil has one of the highest concentrations. My family is from Mississippi, so as kids we used to line up for our cod liver oil.

TR: Can you get enough D from your diet?
CHW: It’s hard; vitamin D is something the body was meant to make. I’m a strong proponent of vitamin D, so I recommend supplements.

TR: What do you take?
CHW: I’m not necessarily the best patient, but I try and take 1,000 IU a day.

Linda Villarosa is a health columnist for The Root. Passing for Black is her first novel.

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