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Q&A on Vitamin D With Michael Holick

The nutrient's benefits, the best ways to get it and how much you really need

Vitamin D has been racking up a stellar list of health benefits, especially for people over 50. Just ask Michael Holick, M.D., professor of medicine, physiology and biophysics at Boston University Medical Center and author of The Vitamin D Solution.

When it comes to vitamin D, Holick follows his own advice. "I'm over 50 and I drink three glasses of milk a day as well as take a multivitamin and a 2,000 IU vitamin D supplement. I also like to cycle, play tennis and garden. When I do, I always protect my face from the sun with sunscreen and a broad-brimmed hat, but I don't use sunscreen on my arms or legs."

Here, he answers questions about the sunshine vitamin.

Q. Why does vitamin D benefit men and women over 50?

A. We have good evidence that increasing vitamin D intake will improve muscle function and reduce the risk of falling and fracturing a hip, developing several different types of cancer, having a heart attack and developing diabetes.

Q. How much vitamin D do I need?

A. I recommend that people over 50 take supplements of at least 2,000 IU of vitamin D a day, either as vitamin D2 or vitamin D3. Both are equally as effective.

The best source of vitamin D is the sun, so in addition to supplements, I suggest that adults expose their bare arms and legs to sunlight between the hours of 10 a.m. and 3 p.m. two or three times a week. Of course this isn't possible in winter if you live in the North, but you can in spring, summer and fall. Stay in the sun for only half the time it would take to get a mild sunburn and always be sure to protect your face with sunscreen and a broad-brimmed hat. And don't forget sunglasses.

Q. Do I have to take my vitamin D supplements every day?

A. No. You can take them daily, weekly or even monthly as long as the total dose is the same, that is, at least 2,000 IU a day. If you prefer a once-a-week schedule, take 14,000 IU on one day of the week. You can take it either with food or on an empty stomach.

Q. What foods contain vitamin D?

A. Wild-caught salmon, fresh mushrooms exposed to ultraviolet light, sun-dried shiitake mushrooms, and fortified milk and orange juice are all good sources.

Q. Can I take too much vitamin D?

A. Adults can take up to 10,000 IU a day with no ill effects.

Q. Can my skin produce vitamin D if I sit in the shade or get sunlight through a window?

A. No in both cases. You have to be exposed to direct sunlight. But you can still get a sunburn.

Q. I'm over 50 and don't take vitamin D supplements. Should I be tested for a vitamin D level?

A. If you're not taking at least 2,000 IU of vitamin D a day, chances are your levels are too low. The only sure way of knowing is to have a 25-hydroxy vitamin D test, also called a 25 (OH) D test. Vitamin D sufficiency begins at 30 nanograms per milliliter [30 ng/mL].

Nissa Simon writes about health issues and lives in New Haven, Conn.

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