Istock Ninety to 95 per cent of the vitamin D in your body comes from sun exposure.

You know vitamin D is important for your health, and you’ve likely read that hardly anyone gets enough of it.

Many studies suggest that maintaining the amount of D recommended by the National Institutes of Health — 30 to 50 nanograms per millilitre in your blood — can help ward off high blood pressure, multiple sclerosis, fibromyalgia, diabetes, depression, some cancers and muscle weakness.

So how do you keep up a healthy level of vitamin D?

The best way is exposure to the sun in warmer months. “Ninety to 95 per cent of the vitamin D in your body comes from sensible sun exposure,” Dr. Michael F. Holick, professor of medicine, physiology and biophysics at Boston University School of Medicine, 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 per cent. 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.

“For some people, it could be 10 minutes, for others it can be 15,” says Dr. Houman Danesh, director of integrated pain management at Mt. Sinai in New York City.

How can you get enough vitamin D from the sun during winter? Your body will access the vitamin D in your fat cells, and because most people don’t get enough sun to make this crucial vitamin year-round, taking a supplement can also help.

Although the Institute of Medicine recommends 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. Pregnant and lactating women and the obese need more. Breast milk doesn’t contain vitamin D, so Holick says that even breastfeeding infants need a daily supplement.

It’s also impossible to get all the vitamin D you need from food. 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.”

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