Vitamin D: Sunshine and So Much More
If this vitamin isn’t in your medicine cabinet, it probably should be.
February/March 2008
By Linda B. White, M.D.
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Our chief source of vitamin D is sunshine.
VEER.COM/DIGITAL VISION PHOTOGRAPHY
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What do the following conditions have in common: osteoporosis, multiple sclerosis, high blood pressure, diabetes and cancer? Give up? Experts suspect that insufficient levels of vitamin D raise your risk of getting these diseases. Unfortunately, most of us probably are vitamin D deficient.
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About all I was taught in medical school is that vitamin D keeps bones strong. Recently however, this area of study has exploded as scientists uncover the vitamin’s far-reaching effects. Because it increases calcium levels, vitamin D indirectly fortifies bones and teeth. It also regulates cells all over the body, which explains vitamin D’s disparate roles, such as influencing insulin production and immune function, as well as helping prevent inflammation and cancer.
The scary thing is that vitamin D deficiency appears to be quite common. A recent British study found that 87 percent of volunteers had low blood levels of the vitamin in winter and spring, and 61 percent had low levels in summer and fall. Why the seasonal variation? Our chief source of vitamin D is sunshine.
Why We’re D-ficient
In response to ultraviolet B (UVB) rays in sunlight, our skin transforms a derivative of cholesterol normally found in the skin into vitamin D3 (cholecaliferol). The liver, kidneys and other tissues further activate this molecule. Given that the skin is a veritable vitamin D factory, why is deficiency so rampant? History — ancient and recent — holds the answers.
Humans evolved near the equator and spent days outdoors, allowing the skin to generate ample amounts of this vitamin. About 50,000 years ago, some of our ancestors migrated toward the poles, where winter sunlight isn’t intense enough for vitamin D production. However, their diet of vitamin D-rich fish compensated for the deficit.
But rickets became prevalent in the 18th century during the Industrial Revolution, when people shifted to indoor labor and the skies darkened with pollution. This manifestation of severe vitamin D deficiency causes skeletal deformities, such as bowed or knocked knees and bony knobs along the ribs, known as rachitic rosary. During the 1930s, the decision to add vitamin D to milk nearly eradicated rickets in the United States. But nowadays, kids and adults drink less milk and more juice and sodas, and sadly, rickets is making a comeback in American children according to a study released last year.
Starting about 30 years ago, another cultural shift deepened our vitamin D deficit: public health campaigns to avoid the midday sun, cover up and apply sunscreen. They were justified attempts to save our skins from sun-induced aging and cancer, but now we’re not making enough vitamin D. These days, vitamin D deficiency has become commonplace, even in the tropics. For instance, a sampling of adults in sunny Honolulu showed that half were low in D.
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