Q: For years, experts have told us to avoid sunlight, but now I'm hearing that this leads to deficiencies in vitamin D. What should I do?
-Catherine H., Sausalito, Calif.
Homo sapiens evolved in Africa as a hairless ape, a creature that spent most of its time outside in a sunny environment. Today we've become largely indoor mammals that usually cover up when we venture outside. Even when we sit on a beach, we usually slather ourselves with sunscreen. That lack of sun exposure means that our bodies synthesize less vitamin D than our distant ancestors did, a condition that's led to widespread vitamin D deficiencies in modern humans.
If you want to know how much our bodies crave D, just take a look at how hard they work to replenish it. People who are extremely deficient in vitamin D (less than 12 ng/mL) respond rapidly to sun exposure, and their serum levels rise extremely quickly. People who are marginally deficient (30-50 ng/mL) achieve optimal levels (50-80 ng/mL) more slowly. This is evidence that we need to maintain a minimal level to be fit.
One exception to this rapid repletion is the obese. It's very difficult to get obese people "up to speed" with vitamin D, because, as a fat-soluble vitamin, it "hides" in the fatty tissues. In order to build up enough, some people require very high-dose supplementation-20,000 or more IU daily as prescribed by a doctor. While that seems like a lot, it's sometimes necessary for repletion, which is important because this vitamin plays many crucial roles in the body.
It has become common knowledge that vitamin D is very important for bone density-equally, if not more so, than calcium. But research also shows that vitamin D3 can help slow the progress of various autoimmune diseases, including multiple sclerosis. There's also evidence that lupus outcomes are improved with adequate serum vitamin D levels.
Additionally, vitamin D has been shown to improve asthma, especially in patients who don't do well with inhalers. It can also improve arthritis, and it's been noted to improve mood.
Possibly the most interesting tidbit about vitamin D, however, is its effect on telomeres-the protective caps on the ends of our chromosomes. Every time a cell replicates, and the DNA divides, a little bit of the telomere tip is lost, leading inexorably to aging. But studies have shown that vitamin D can help lengthen telomeres, thus slowing the aging process by helping extend telomere life.
Maintaining optimum vitamin D levels, then, is key to good health and long life. But that's not always easy. In addition to lack of sun exposure, modern humans also tend to be vitamin D deficient because we also don't consume enough in our diets. In fact, the best natural sources of vitamin D are foods that many of us don't eat at all-fish livers and other organ meats. Plus, our culture tends to be extremely fat phobic, which means we're consciously avoiding even more chances to obtain this fat-based vitamin.
Today, most physicians are tuned into the problem, so ask your doctor to check your vitamin D levels before another winter rolls around. If you need to supplement, cholecalciferol, or vitamin D3, is what you want. Don't be fooled into taking the vegetable form D2, also known as ergocalciferol, which is far more expensive and doesn't work as well.
For optimal absorption, always take your vitamin D with fat-a spoonful of full-fat yogurt, or anything containing eggs, meat, or olive oil, for instance. And make sure that your vitamin D supplement is oily. Dry D doesn't work as well.
Just The Facts
Probably the most important early warning that we, as a society, had become deficient in this broadly useful, fat-based vitamin, was an article by Reinhold Vieth of the University of Toronto. Published in 1991 in the American Journal of Clinical Nutrition, Vieth's article "Vitamin D Supplementation, 25-hydroxyvitamin D concentrations, and safety" was recently cited by John Cannell, MD, now considered the leading expert on vitamin D, as the revelation that led him to dedicate himself to the study of this important nutrient. For the latest information on everything to do with D, visit Cannell's website at www.VitaminDCouncil.org.
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