This powerhouse vitamin, which acts like a hormone in the body, has captured the media spotlight over the last few years and is likely to remain there, thanks to study after study linking it to (seemingly) every ailment. Researchers at Oregon State University’s Linus Pauling Institute in Corvallis studying the role nutrient deficiencies play in chronic diseases point out that one billion people worldwide are D deficient. “Vitamin D is a very good general biomarker for health— just like cholesterol, blood pressure and your body mass index,” says James Dowd, M.D., a rheumatologist and co-author of The Vitamin D Cure (Wiley). “People who have low levels are at risk for colon, breast and prostate cancers, heart attack, hypertension, Parkinson’s and dementia.” But before you race to the supplement aisle, Dowd urges patients to take a look at the lifestyle choices that could also be contributing to the deficiency. “People think they can just take a pill and solve the problem, but your lifestyle is the root of the issue.” Dowd notes that deficiencies have reached such huge proportions for a few reasons. First, we’re wearing more sunscreen and spending less time outdoors, so we’re not getting the UVB rays that prompt the body to manufacture vitamin D. In addition, we’re eating processed, sugary foods that spike insulin levels, which sends vitamin D into fat stores instead of keeping it in the blood where different body systems can use it. Finally, we’re not exercising as much as we should be. Exercise helps keep blood sugar stable, lowers insulin levels and burns fat stores, freeing up more vitamin D.
The recommended dose: The Recommended Dietary Allowance (RDA) for adults is 600 IU (if you’re over 70, it’s 800 IU), according to the Institute of Medicine. If you’ve been told you’re low, Dowd recommends taking 20 IU of vitamin D3 (not D2) per pound of body weight daily, or about 3,000–4,000 IU per day for the average 150-pound woman. “Therapeutic amounts are higher than the RDA,” explains Dowd, “because you’re trying to come back from a deficiency.” Once you’re back in normal range again, he says, you can go back to taking just the RDA.
Warning signs: Since D affects so many bodily functions, it can be hard to pinpoint specific signs and symptoms of a deficiency. But fatigue is common, and any kind of long- term issue where you’re just not feeling right is a cue to see your doctor.
Who’s at risk: People with darker skin such as African-Americans and Hispanics have a tougher time getting enough vitamin D because their increased melanin levels block UVB rays. The elderly, obese, anyone living in low-sun environments, and those suffering from Crohn’s disease or other gastrointestinal disorders or kidney disease might also have a hard time making or using D. Vegans as well as anyone with milk allergies will also have to work harder to get adequate amounts. Get tested: Ask your doctor for a 25-hydroxyvitamin D blood test. Dowd says your risk of disease increases if your blood levels of D are below 30 nanograms per milliliter (ng/mL); between 40 and 60 is ideal.
How to get it: Fifteen minutes of daily sun exposure without sunscreen will do it, unless you’re in a northern latitude (above the level of San Francisco in the U.S.) where the sunlight is weaker. In that case you’ll need more. “There aren’t many good natural food sources of vitamin D, so you have to look for fortified dairy,” says Liz Applegate, R.D., director of sports nutrition at the University of California at Davis. Canned salmon and other fatty fish, egg yolks, cultured soy and kefir are good options, too.
Best buy: Nature’s Way Vitamin D3 (2,000 IU) ($6 for 120 softgels; drugstore.com); Premier Research Labs D3 Serum ($11 for .05 ounces; purelifenutrition.com)