The list of illnesses that might be prevented by getting enough vitamin D seems to grow every day. Many studies suggest that maintaining the amount of D recommended by the National Institutes of Health – 30 to 50 nanograms per milliliter in your blood – can help ward off high blood pressure, multiple sclerosis, fibromyalgia, diabetes, depression, some cancers and muscle weakness, in addition to thwarting the long-established risks of rickets in children and osteomalacia (which weakens bones) in adults.
“It's only been in the last 10 years or so that we've started to understand more of what vitamin D does,” says Dr. Houman Danesh, director of integrated pain management at Mt. Sinai in New York City. “It affects every system in the body. The main thing that it does though is help with the absorption of calcium. If your body doesn't absorb enough calcium, it leeches it from our bones.”
You know vitamin D important for your health, and you've likely read that hardly anyone gets enough of it. You might also have heard warnings that too much vitamin D can be toxic, causing constipation, confusion or kidney stones – but experts say that ODing on D is likely more difficult than you think.
“People tend to think that if a little is good, a lot is better, so some have raised concerns about the risk of toxicity,” says Dr. Michael H. Holick, professor of medicine, physiology and biophysics at Boston University School of Medicine. “But vitamin D toxicity is one of the rarest medical conditions; you would need to take thousands of IUs every day for months for your body to take in enough to be harmful.”
So how do you keep up a healthy level of vitamin D? From these three sources:
The best way to get enough vitamin D is exposure to the sun in warmer months.
“Ninety to 95 percent of the vitamin D in your body comes from sensible sun exposure,” Holick says.
Skin needs to be exposed directly to the sun for your body to make vitamin D. A product with SPF 30 decreases your ability to make vitamin D by 95 percent. Because dermatologists have been telling us for decades to never expose unprotected skin to the sun's cancer-causing rays, many people are understandably confused about how to get enough vitamin D from sun exposure — especially because there's no set exposure standard that can be applied to everyone.
“For some people, it could be 10 minutes, for others it can be 15,” says Danesh, who recommends Dminder.info, an iPhone app that tracks the amount of vitamin D you're getting from the sun and helps keep you from burning, based on your skin and location.
How can you get enough vitamin D from the sun during winter? You can't if you live north of Atlanta. Your body will, however, access the vitamin D in your fat cells during the winter, Danesh says. But most people benefit from supplementing, Holick says.
Because most people don't get enough sun to make this crucial vitamin year-round, taking a supplement can help. Doctors usually recommend getting vitamins from food sources rather than supplements, but vitamin D is a special case.
Although the Institutes of Medicine recommend 400 to 600 IUs of vitamin D for children and 600 to 800 for adults, Holick recommends 600 to 1,000 for kids, and as much as 2,000 to 4,000 IUs daily for adults. The Endocrine Society's recommendations are also higher: 600 to 1,000 for kids and 1,500 to 2,000 for adults. Pregnant and lactating women and the obese need more and should consult their doctors about how much D they should supplement. Breast milk doesn't contain vitamin D, so Holick says that even breastfeeding infants need a daily supplement.
The bottom line: It's not possible to get all the vitamin D you need from food. For example, egg yolks are often recommended as a food source of vitamin D, but they only have 40 IUs per yolk. Similarly, you would need to eat wild-caught salmon and other fatty fish such as mackerel and herring every day to get enough D. Vitamin D is added to many foods, such as milk, juice and cereal, however, and mushrooms can be irradiated with good amounts of vitamin D as well.
Because of conflicting recommendations and research about what vitamin D actually does, “doctors are struggling with who to check, if they should check and when to check vitamin D levels,” says Dr. Robert Graham, an internist at Lenox Hill Hospital in New York City.“But I would argue that you need to get tested first to know at what level you are starting with, and figure out how much you need to supplement from there.”