Although there are many Canadians who love to brave the outdoors in winter, many more shield themselves from the cold in their homes, shunning one of nature’s most important nutrients: vitamin D.
Vitamin D is both a nutrient and a hormone that works with calcium and phosphorous to strengthen bones. The human body naturally produces this vitamin through exposure to sunlight. Calcium can reach its optimal level only if your body has enough vitamin D.
“Unfortunately, in Canada between October and April, there just aren’t enough ultraviolet rays from the sun to get very much vitamin D in your skin,” says Dr. Jonathon Maguire, a pediatrician and researcher at St. Michael’s Hospital in Toronto.
Without enough vitamin D, children can get rickets, a disorder that leads to softening and weakening of their bones. In older adults, lack of adequate vitamin D and calcium can lead to osteoporosis, a condition that makes bones brittle and fragile.
“People are being cautious to make sure they have enough vitamin D to avoid things like that,” says Maguire, who has researched and written papers on vitamin D.
In some cases, vitamin D also can help to ward off heart disease and illnesses such as multiple sclerosis, he adds.
Vitamin D also helps to send essential signals throughout the body, says Dr. Reinhold Vieth, a retired professor who taught in the University of Toronto’s faculty of medicine and is an advisor to the Vitamin D Society.
“Vitamin D is a raw material the body uses to communicate information between the body’s tissues and its cells,” he says. “Think of vitamin D as if it were a blank piece of paper: it’s not the message itself, but it’s the carrier for the written word. When we don’t have enough paper, we can’t communicate and mistakes happen.”
There has been some controversy of late regarding how much vitamin D is enough. Health Canada recommends supplemental vitamin D of 400 international units (IUs) for infants and young children who are breastfed or receiving breast milk. Children have a recommended dietary allowance of 600 IUs a day, and this level remains constant until age 70, when the intake should be 800 IUs a day.
“It has been formally recognized, and has been for a long time, that vitamin D is the one thing that Canada’s [Food Guide] diet does not provide the recommended amount of,” Vieth says.
In developed countries such as Canada, vitamin D can be found in foods, to some extent, especially in fortified cow’s milk and margarine, fatty fishes such as salmon, as well as liver and egg yolks. One tablespoon of cod liver oil contains about 1,300 IUs.
But using just food to get your required amount of vitamin D can be difficult, says Vieth. The Dieticians of Canada’s website states that two cooked egg yolks provide only 57 to 88 IUs of vitamin D. Vieth notes the average Canadian’s daily intake of vitamin D is around 300 IUs.
Much of the human body’s vitamin D comes from exposure to sunlight. As there’s not enough sunlight in Canada to produce sufficient vitamin D, especially during the winter months, extra dietary sources and/or supplements may be used.
There are two kinds of vitamin D: D2, which comes from plant products; and D3, which comes from animal products. There is debate regarding whether one kind works better, says Maguire.
“Both work and increase vitamin D stores in people’s bodies, but there is some evidence that vitamin D3 may be a little more potent than vitamin D2,” he says. “So, for people concerned about eating animal products, they may wish to take vitamin D2 – but they may need to take a little more vitamin D2 to have the same effect as [taking] vitamin D3.”
The most a person can take without a doctor’s supervision and still be guaranteed to be safe is 4,000 IUs a day, says Vieth.
Vitamin D can stay in the body for a long time. Without any sun or supplements, a person’s vitamin D level will drain out by half in about two months. Although staying in the sun is the best way to get vitamin D, too much sun is not a good thing, either, Maguire says.
So, as with everything else, moderation is best.
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