Source: Web exclusive, January 2011
You’ve probably read plenty about the reported health benefits of vitamin D. But the amount of the so-called sunshine vitamin that one needs to be healthy remains confusing. While Health Canada recommends that adults under the age of 50 take a daily supplement of 200 IU (400 IU for adults over 50), organizations such as Osteoporosis Canada and the Canadian Cancer Society recommend 400-1,000 IU daily in fall and winter.
New guidelines on vitamin D were recently released by the Institute of Medicine in the U.S. But if you were hoping for resolution on how much vitamin D is enough from the long-awaited report commissioned by Canadian and U.S. governments, you’ll be disappointed. The Institute of Medicine committee reviewed available research, and concluded in its report, Dietary Reference Intakes for Calcium and Vitamin D, that there just isn’t enough solid evidence to make the case for significantly increasing vitamin D levels to help prevent diseases such as heart disease and cancer. Instead, it recommends a slightly increased daily intake of 600 IU for the average adult, based on evidence it felt was consistent to support bone health.
So is this new recommendation enough? We asked leading experts on both sides of the debate to weigh in with their thoughts to help you decide for yourself.
It’s not enough
Susan Whiting, professor of nutrition at the University of Saskatchewan and co-author of Statistics Canada’s Canadian Health Measures Survey (which assessed vitamin D blood levels in Canadians between 2007 and 2009): I do not think they went quite far enough in terms of making recommendations for all of the health actions vitamin D has. They made a very conservative recommendation based on bone health. The [IOM report reviewers] seem to think that the evidence for vitamin D and colon cancer and immune system risks is inconsistent. But by only looking at rigorous randomized controlled trials (RCTs), they eliminated the possibility of looking at other really good evidence out there. For example, there is a Nebraska cancer trial that showed a reduction in cancer in those who took 1,000 IU vitamin D daily, but it was not considered because of a technicality. On the other hand, they kept in the Women’s Health Initiative, where participants only took 400 IU daily, which is barely enough to make a difference. I agree that there needs to be more research on vitamin D and various health outcomes, but they could have increased the recommended amount to 800 or 1,000 IU for persons over 50 years, ensuring bone health and benefits such as preventing cancer and protecting the immune system safely.
It is enough
Krista Eslinger, Nutrient Advisor, Health Canada’: The IOM committee really did take a close look at all of the evidence available, and the reason it made the recommendation of 600 IU for bone health was because the evidence for other health outcomes such as cancer and cardiovascular disease was inconsistent, inconclusive and did not show a clear cause and effect relationship. The committee looked at RCTs as well as observational studies: it looked at the totality of the evidence. It’s not like it totally discounted the relationships shown in research between vitamin D and cancer, for example. But what it concluded was that at this point the relationships are not strong enough to make a public recommendation in that regard. We find the report sound, well documented, and agree with the conclusion.
Are Canadians deficient in vitamin D?
Whiting: The challenge is equating blood levels with intake levels and in deciding on a cut-point. (In other words, we don’t know enough to say exactly how much vitamin D is needed for any particular condition, and therefore it’s tough to say with accuracy what is a deficiency.) In the clinical world, we have cut-off points for high cholesterol or iron deficiency. We don’t have that for vitamin D. Some say it is at least 50 nanomoles per litre (nmol/L) for bone health, however the IOM report indicates that 50 nmol/L is generous. Based on that, the IOM said that 87 percent of Canadians are above the amount of blood levels of vitamin D required for bone health. But they need to determine why some people were above in the winter and some were below. Maybe some of the Canadians studied were already taking supplements in the winter (they didn’t ask that). Certainly there are subgroups, people who are not of European origin, people who never get sun exposure even in the summer, and older people, who are at risk of being vitamin-D deficient. To say everything is fine in regard to vitamin D levels, which is what Health Canada recently announced, is not okay. There are still 15 percent of people, maybe more, who are vitamin D deficient.
Eslinger: The Health Measures Survey did only look at blood status. There was a question about whether participants were taking a supplement, but it was a generic question, not specific to vitamin D. We are looking to try to assess that in the future. It will be an important piece of information to help guide future policy. And we do know that 10 to 15 percent of the population is vitamin-D deficient for what has been determined to be an adequate cut-point for bone health. But we don’t know who they are.
Will the Canadian Cancer Society lower its recommended vitamin D intake based on the new report?
Heather Chappell, director of Cancer Control Policy at the Canadian Cancer Society: We made the recommendation of 1,000 IU of vitamin D for Canadian adults in fall and winter in 2007 based on research at the time. We were comfortable with that, and we still are, because the research showed a relationship between vitamin D and colon cancer, and breast cancer. We recognize that there is no definitive evidence (proven cause and effect) in terms of the optimal dose of vitamin D, but we also feel that there is enough scientific evidence to provide guidelines while research continues.
Eslinger: I can’t speak to how the Canadian Cancer Society reviewed the evidence. What I can say is that the amounts being recommended by other health organizations are well within what is considered to be a safe upper intake level (the IOM report increased that 2,500 IU daily, for adults 19-50 years old).
What the bottom line for the average Canadian?
Whiting & Eslinger: The key message at this point in time is that vitamin D intake amounts will differ for everyone depending on your risk profile. Talk to your doctor before adding a vitamin D supplement to your daily regimen. A professional can help you assess how much vitamin D you are getting from diet and sunshine, and, take into account the various guidelines and your risk factors for vitamin D deficiency in order to make the best recommendation.
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