How much vitamin D is enough?

Osteoporosis Canada has released updated recommendations on how much vitamin D adults should be taking to keep their bones strong.

TORONTO — Osteoporosis Canada has released updated recommendations on how much vitamin D adults should be taking to keep their bones strong.

The new guidelines, published in this week’s edition of the Canadian Medical Association Journal, better reflect research findings about the so-called sunshine vitamin and what should be considered “adequate intake” and the “tolerable upper level.”

“The last comprehensive update to the Canadian Osteoporosis guidelines came out in 2002, and there’s been a lot of new work that’s taken place in the last eight years,” said Dr. Bill Leslie, chair of the organization’s scientific advisory council.

“So we felt it was important, given the public’s interest in this and the new emerging scientific data, that we look at our previous statements,” Leslie said from Winnipeg. “And in so doing, (we) saw that the previous recommendations made needed to be updated.”

The new guidelines, issued Monday, recommend daily supplements of 400 to 1,000 international units for adults under age 50 without osteoporosis or conditions affecting vitamin D absorption.

Adults over 50, with or without the bone-thinning disease, should take between 800 and 2,000 IUs a day, said Leslie, a professor of medicine at the University of Manitoba. “I think that individuals can be very confident that 1,000 units a day is a very safe dose. In fact, even 2,000 units a day is considered safe and is what’s called the tolerable upper limit.”

Vitamin D is made by the body through the skin’s exposure to ultraviolet rays from the sun. Recent studies have shown that many Canadians — starved of adequate sunlight during the fall and winter months — are deficient in the fat-soluble vitamin.

In summer, though, 20 minutes of full sun for a person in shorts or a bathing suit is all you need.

Only a few foods naturally contain significant amounts of the nutrient (fatty fish and fish oils), but some dietary staples are fortified with vitamin D, including milk and other dairy products.

While vitamin D is needed to maintain normal blood levels of calcium and phosphorus, it is also essential for the absorption of calcium to form and maintain strong bones. A chronic deficiency can contribute to the development of osteoporosis, which can lead to fractures, especially in older adults.

“That’s an individual where it’s even more important to ensure optimal vitamin D status,” Leslie said of older people with thinning bones.

A simple blood test can determine by how much a person is deficient, then vitamin D supplementation can be prescribed to raise the level, he said. “And some individuals may need more than 2,000 units a day. But you should only do that under medical supervision.”

Health Canada says adequate daily vitamin D intake for anyone aged two to 50 is 200 IUs, which it says can be obtained through fortified dietary products. However, the federal department advises that all adults over 50 should also supplement their diet with 400 IUs of vitamin D daily.

The advice is based on “dietary reference intakes” (DRIs) established in 1997 by a panel of Canadian and American scientists under the auspices of the Institute of Medicine. Following a slew of recent studies on vitamin D, those DRIs are now under review by a new committee, which is expected to issue its report in the fall.

Three years ago, the Canadian Cancer Society released its own guidelines, based on research suggesting that vitamin D may boost the immune system and reduce the risk of some cancers. The society says all adults should consider taking 1,000 IUs a day during the fall and winter. Those at higher risk of insufficiency, among them older people and those with dark skin, should consider taking that amount all year round.

Leslie concedes that the various recommendations from different health organizations are sure to leave some Canadians confused about how much vitamin D they should be taking.

Osteoporosis Canada decided to set out ranges of vitamin D intake because there haven’t been definitive studies “to say this is the right dose … and we certainly would like to see better research done to nail that down,” he said, noting that the guidelines do not deal with children.

“All groups will interpret the data somewhat differently and, of course, at the point people make the recommendations there is different data available,” he said. “It’s a field that is advancing almost weekly with new reports.”

“But what the commonality is of all of these groups is the recognition that Canadians are at risk for vitamin D insufficiency and that there’s a benefit to supplementation.”

Dr. Reinhold Vieth, director of the Bone and Mineral Laboratory at Mount Sinai Hospital in Toronto, said he is glad to see the direction that Osteoporosis Canada has taken with its guidelines.

“I was expecting them to simply reiterate 800 units per day,” he said, referring to the amount of vitamin D the group recommended in 2002.

As to how much an individual should take, given the wide dose range in the new guidelines, Vieth said Canadians should not be afraid of taking vitamin D because it’s a “very forgiving molecule.”

“You don’t have to exactly take every dose every day, just make sure you keep taking it,” he said. “It’s a cumulative thing … Don’t be afraid of doubling up your dose if you’ve missed a day or two.”

In fact, the guidelines’ authors say, some patients may find it more convenient to take their vitamin D weekly in a dose of 10,000 units.