Vitamin D: Boost Strength, Prevent Chronic Disease
Stacks of research link vitamin D deficiency to heightened risk of heart disease, cognitive decline, and even cancer. Studies also show that getting enough of the vitamin can give immediate benefits: D bolsters your immune system to fight off infectious diseases like the flu, and because it ups the calcium you absorb from food, it helps prevent bone loss, which can begin in your thirties.
There's a modern-day reason most of us aren't getting the 2,000 IU of vitamin D many experts say we need: We shun the sun. On average, it takes 10 to 30 minutes of midday UV exposure, without wearing sunscreen, to prompt your body to generate between 10,000 and 20,000 IU of vitamin D, says Dr. John Cannell, executive director of the nonprofit Vitamin D Council. But we can fall way short of that, even in the summer. "Most of us sit at a computer all day, then walk to and from our cars when the sun is too low to produce UV," says Robert Heaney, an endocrinologist at Creighton University. "It doesn't matter where you live. We've evaluated vitamin D statuses of hospital workers in Hawaii and Alaska, and they're exactly the same." Compounding this deficiency problem is the fact that, as you age, your body becomes less efficient at synthesizing the vitamin. According to a report from the Berkeley School of Medicine, a 70-year-old man synthesizes only about a quarter as much vitamin D as a 20-year-old who gets the same sun exposure.
You can't count on food, either. "Even vitamin D–fortified eggs and milk are basically useless," Cannell says. "You would have to drink 50 glasses of milk per day to get enough."
How Much You Need: "As a rule of thumb, get 30 to 35 IU per pound of body weight per day," Heaney says. (So again, if you're 165 pounds, that's about 5,000 IU.) Downing megadoses won't give you more benefit, and it may cause calcium buildup in the blood vessels, cautions JoAnn Manson, an epidemiology professor at the Harvard School of Public Health.
Make sure you buy vitamin D3, not D2. D3 is what you'd make from the sun, while D2 is synthetic and takes longer to convert to a usable nutrient in the body, Heaney says. That means you need higher doses and have to take it more often to get the benefits, he says. Finally, take the pill with a meal. Vitamin D is fat soluble, says Dr. Tod Cooperman, president of ConsumerLab, and you may absorb up to 50 percent more if you pair it with food.