American Diets May Lack Vitamin D

Credit: stock.xchng (Image credit: stock.xchng)

A friend recently told me about how his uncle had heard that garlic could help lower his high blood pressure. So the uncle generously added garlic salt to his diet.

A little knowledge can kill you.

A similar misunderstanding appears to be spreading about vitamin D. More and more people are realizing that they are lactose intolerant. So they eliminate milk from their diets.

People also are worried about sun exposure and skin cancer, so they slop on sunscreen whenever they go out or otherwise avoid direct sunlight. And mercury is scaring folks away from eating fish.

As a result, some people are losing all sources of vitamin D. For the first time in a century, doctors are seeing a resurgence in rickets, that bone-deforming disease once endemic to wobbly-kneed child laborers in the Victorian era who never saw the light of day.

Pediatricians in Philadelphia have reported more than 150 new cases in the past three years, up from about zero. Washington, D.C., and other areas with large African-American populations are reporting the similar increases.

No formal studies have found the precise cause of the rickets — be it less milk consumption, less sun exposure, or other factors — but it does appear that Americans in general aren't getting enough vitamin D.

Vitamin Q and A

Vitamin D is a complicated essential micronutrient. The National Institutes of Health convened a panel of experts last September to establish nutritional guidelines. As revealed in the official meeting proceedings, published in the August 2008 issue of the American Journal of Clinical Nutrition, they couldn't come to any consensus. The published overview is essentially a collective shrug of the shoulders.

Vitamin D is crucial for calcium metabolism — namely, the making of strong bones — and likely for immune function, heart health, cell proliferation and cancer and diabetes protection, at a minimum. An independent study from Johns Hopkins University, published in the current issue of the Archives of Internal Medicine, associated lower levels of vitamin D in the blood with a higher risk of death.

Yet the experts couldn't agree to any details. The current recommendation is to get 400 IU of vitamin D daily. Many say this isn't enough, but no one knows how much more is too much.

Complicating issues further is the fact that vitamin D is the only nutrient that can be made entirely in the skin upon exposure to sunlight, yet this varies greatly with skin color and latitude. It's hard to assess your daily dose. Few foods other than fish contain vitamin D. Milk is fortified with it, but you need four glasses to get 400 IUs.

Out of Africa

Lighter skin is more efficient at producing vitamin D. So African-Americans are at a double disadvantage for synthesizing vitamin D from sunlight — in the United States. Their darker skin blocks the ultraviolet light that triggers this chemical reaction. In their native lands, closer to the equator where sunlight is more direct, their darker skins would have enough sun exposure to synthesize vitamin D.

Peoples in high northern latitudes, such as Europeans, slowly developed lighter skin over tens of thousands of years to adapt to the weaker sunlight to generate enough vitamin D to survive. African-Americans forced migration from Africa occurred over a period of only a few hundred years.

Also, most African Americans — and most of the world, actually — are lactose intolerant and cannot digest cow milk well. So many do not drink enough milk. Natural sources of vitamin D include cod liver oil (as if anyone can stomach this, let alone find it outside their great-grandmother's cupboard) and salmon and mackerel (tasty, but expensive).

In Philadelphia many rickets cases involve children of Black Muslims, and the culture of conservative clothing likely played a role.

Yet doctors wonder whether the African-American communities are providing a warning call for all of America, as kids of all races drink less milk, the primary albeit artificial source of vitamin D for most clothed, non-farming residents of North America.

Killer rays

More sunlight isn't the answer. Humans evolved to frolic naked in the sun but also to live about 30 years or so in Africa. Take your fair skin better suited for Scandinavia and place it in Miami for several summers, and you're going to get skin cancer.

Regardless, for latitudes north of New York City, and considering how people bundle up during winter, there's not enough sunlight year-round to satisfy the daily vitamin D requirement.

Milk fortification works well. But all vitamin D supplementation and fortification is essentially created equal. Look for new vitamin D recommendations later this year that try to make sense of the ambiguous NIH report.

Christopher Wanjek is the author of the books "Bad Medicine" and "Food At Work." Got a question about Bad Medicine? Email Wanjek. If it’s really bad, he just might answer it in a future column. Bad Medicine appears each Tuesday on LiveScience.

Christopher Wanjek
Live Science Contributor

Christopher Wanjek is a Live Science contributor and a health and science writer. He is the author of three science books: Spacefarers (2020), Food at Work (2005) and Bad Medicine (2003). His "Food at Work" book and project, concerning workers' health, safety and productivity, was commissioned by the U.N.'s International Labor Organization. For Live Science, Christopher covers public health, nutrition and biology, and he has written extensively for The Washington Post and Sky & Telescope among others, as well as for the NASA Goddard Space Flight Center, where he was a senior writer. Christopher holds a Master of Health degree from Harvard School of Public Health and a degree in journalism from Temple University.