Vitamin D helps prevent and treat osteoporosis. (Mark Gollom/CBC)

Canadian adults can take more vitamin D supplements than recommended under previous guidelines, Osteoporosis Canada says.

Current Canadian recommendations for vitamin D intake are more than 10 years old and are based on preventing rickets, not properly conducted dosing studies, researchers said in Monday's issue of the Canadian Medical Association Journal.

The new guidelines recommend daily supplements of:

• 400 to 1,000 IU for adults under age 50 without osteoporosis or conditions affecting vitamin D absorption.
• 800 to 2,000 IU for adults over 50.

"A daily supplement of 25 micrograms (800 IU) should now be regarded as the minimum dose," wrote Dr. David Hanley of the University of Calgary Health Sciences Centre and his colleagues.

For people who need added supplementation to reach optimal vitamin D levels, doses up to the current 2,000 IU do not require medical supervision, but if higher doses are sometimes needed, then monitoring is appropriate, the guidelines say.

The guidelines note vitamin D deficiency should be regarded as a continuum ranging from deficiency such as rickets and bone mineralization to insufficiency.

Levels too low in Canadian winter

Vitamin D and calcium are important for preventing and treating osteoporosis, which can lead to fractures. Nontraditional roles for vitamin D include thwarting different forms of cancer, staving off multiple sclerosis and autoimmune disorders and fighting infections.

Supplements are needed because diet has little impact, Osteoporosis Canada said.

“Canadians are at risk of vitamin D deficiency from October to April because winter sunlight in northern latitudes does not allow for adequate vitamin D production,” Julie Foley, president and CEO of Osteoporosis Canada, said in a release.

"Also, because vitamin D requirements for an individual may vary considerably depending on many factors, it’s very important to check with your physician about how much vitamin D you should be taking.”

More research is needed into optimal doses and safe upper limits for vitamin D intake, the guideline's authors concluded.

"Despite a great deal of new research in the past decade, these major clinical questions have still not been addressed to the satisfaction of most experts in the vitamin D field," they concluded.

The Canadian Cancer Society and the Canadian Pediatric Society have also both increased their vitamin D recommendations in recent years. Health Canada recommends 200 IU to 600 IU of vitamin D a day.

The new osteoporosis recommendations exclude pregnancy and lactation.

The development of guidelines was funded by the Ontario Ministry of Health and Long-Term Care. Several of the authors declared ties to pharmaceutical companies.