With sales figures showing Canadians becoming a nation of vitamin-D-pill poppers, questions are arising on the best way to take it.
Should it be with a meal? If you forget one day, is it safe to have several days' worth of doses at once? Can you get too much of a good thing and overdose? What about cod liver oil, the favourite vitamin-D treatment from days of yore?
For people who've been ingrained with the one-a-day-concept as the sensible way to take supplements, nutrition experts say vitamin D is a forgiving vitamin, and many different approaches work equally well.
People can pop a lot at once, even a week's worth at a single sitting, with no adverse effects. And unlike the other fat-soluble vitamins, A, E and K, the sunshine vitamin is absorbed well without food, so it can be taken any time.
"Take it on a full stomach, take it on an empty stomach. Take it once a day, take it twice a day. Take it with fat, take it without fat. None of that matters," said John Cannell, head of the Vitamin D Council, a California-based advocacy group promoting the nutrient.
In recent years, vitamin D has emerged as one of the most-hyped vitamins, with many medical experts intrigued by its purported ability to protect against illnesses ranging from flu to cancer.
There has been a flurry of research suggesting that high doses – a few thousand international units a day – might help ward off the diseases in people who don't have enough of the nutrient circulating in their blood. That includes most Canadians in winter, because the sun doesn't get high enough in the sky to make the vitamin the natural way – from exposure of bare skin to strong ultraviolet light.
The vitamin-D winter is now under way throughout Canada. In a city in the extreme south, such as Windsor, Ont., skin synthesis plunges to virtually nothing from November to February, while in more northerly Edmonton the period runs from October to April.
Vitamin D is available as a pill or a liquid. Some manufacturers are trying to cash in on the craze by developing new products, such as chocolate-flavoured pills.
One advantage of vitamin D is that a lot can be taken at once. Reinhold Vieth, a professor in the department of nutritional sciences at the University of Toronto, was part of a research team that in 2008 published results from a study in which they gave three groups of women with hip fractures the equivalent of a daily dose, but at different intervals. Some took 1,500 IU a day, others 10,500 IU once a week or 45,000 IU once in 28 days.
There was no significant difference in their blood levels, suggesting that it's efficacious to take a week's worth or even more at one time. Those popping the vitamin daily can safely double up if they've forgotten one day. "If you don't have to take your medicine as often, you actually take a larger percentage of your medicine," said Prof. Vieth, who has acted as a paid consultant for nutrition companies.
The reason people can take large, one-time doses is that any excess vitamin D is stored in fat and released into the body when needed.
There is currently no consensus on how much to take. Research indicates the anti-cancer properties click in at daily doses of 1,100 IU, but Health Canada only recommends 200 to 600 IU, depending on age. Its recommendation is based on the amount needed for bone health.
Health Canada says people shouldn't take more than 2,000 IU a day, although experts who are advocating for the nutrient believe higher amounts may be needed for optimum health.
In other research, vitamin D was added to orange juice and found to be well absorbed, suggesting that it's not necessary to take it with a fatty substance or a meal.
Susan Whiting, a professor of nutrition at the University of Saskatchewan, said some people worry about getting too much by taking a 1,000-IU pill daily when the nutrient is also in milk and some foods such as oily fish.
"You can still take a multivitamin, drink milk, eat salmon, and you're likely not going to get over 2,000," she said.
Milk contains 100 IU per cup, an egg yolk 20 and farmed salmon between 100 and 250 IU per portion.
Dr. Whiting cautioned about taking vitamin D through cod liver oil, the favourite of parents of yesteryear.
She said the oil is formulated differently than a generation or two ago, and now contains too much vitamin A relative to its vitamin-D content.