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Vitamin D Supplements: FAQ

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Vitamin D is found in some foods, including fatty fish like salmon and tuna, beef liver, fortified dairy products, cheese, and egg yolks. Except for those, getting enough vitamin D from your diet isn’t easy. As examples, a 3-ounce serving of salmon provides 447 IU, and 3 ounces of tuna fish offer 154 IU.

Meanwhile, our skin makes vitamin D when exposed to natural sunlight. This helps vitamin D levels in our blood. But Recker says only people who live at the equator get a large amount of D from sunlight.

Testing: Experts disagree on whether healthy people need routine testing to detect low vitamin D blood levels.

How much is enough: Experts also disagree on how much vitamin D we need in our blood to be healthy.

Which groups of people might benefit more from higher levels of D?

Older adults who are frail, Campos-Outcalt says. Getting 800 IU a day may help them prevent falls and fractures.

Recker says older people who are healthy can also benefit from the higher levels, ''because the skin loses the ability to make vitamin D" as people age. Some older people also stay indoors more as they age, he says.

Other people may also need to pay close attention to vitamin D in their foods. Among them are people on corticosteroids and other medications that can affect bone health, Recker says.

What are the potential harms of excess vitamin D supplements?

Very high doses of vitamin D can cause extremely high levels of calcium in your blood, which can lead to heart rhythm problems, kidney stones and damage, and severe muscle weakness. This calcium excess usually happens if you take 40,000 IU per day for a couple of months or longer, or take a very large one-time dose.

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