Vitamin D supplements' benefits panned in review of studies
Most Canadians probably not vulnerable to low vitamin D levels, experts say
Taking vitamin D supplements to prevent cancer, heart disease, fractures and premature death provide few if any benefits, a new review of studies says.
Vitamin D, the sunshine vitamin, has been supplemented in foods like milk for decades to prevent rickets in Canada and northern Europe.
Vitamin D pills became popular after observational studies linked its use to a reduced risk of multiple sclerosis, diabetes and breast and prostate cancers. But more rigorous randomized control trials don’t support a cause-and-effect relationship between taking the vitamin and gaining health benefits.
Now a review and analysis pooling findings from 40 trials on the effect of vitamin D supplements concludes the pills likely provide few, if any, health benefits.
“In view of our findings, there is little justification for prescribing vitamin D supplements to prevent myocardial infarction or ischaemic heart disease, stroke or cerebrovascular disease, cancer or fractures, or to reduce the risk of death in unselected community-dwelling individuals,” in the general population, Dr. Mark Bolland, of the University of Auckland in New Zealand, and his co-authors concluded in Friday’s online issue of the Lancet Diabetes & Endocrinology.
Critics claim certain people could still benefit from vitamin D supplements, said Glenville Jones, a biochemistry professor at Queen's University in Kingston, Ont.
Jones was part of the Institute of Medicine’s panel in 2011 that concluded the majority of Canadians and Americans are getting enough vitamin D based on national surveys of blood tests.
Vitamin D supplements continue to be important for people living close to the North Pole, those who suffered rickets in childhood and adulthood, osteoporosis or chronic kidney disease, he said.
Jones suggested that people consult their doctor to determine whether their vitamin D levels are low.
"Remember that Canadians can't make vitamin D between October and April, so if we're vulnerable at all it would be at this time of the year. But most of us are probably not vulnerable."
The scientific and medical debate about vitamin D is driven in part by differences in defining vitamin D deficiency and insufficiency, Jones said. A current U.S. government-funded trial of 20,000 people should provide more definitive answers.
The Institute of Medicine's recommendation to the Canadian and U.S. governments is for 600 IU to 800 IU of vitamin D from foods such as salmon, fortified foods or supplements, depending on age.
In a journal editorial on multivitamins last December, Dr. Edgar Miller, a professor of medicine and epidemiology at Johns Hopkins University in Baltimore, Md., wrote that proponents of supplements, including vitamin D, hope the pills will overcome poor diet or behaviour, but the latest research isn’t supporting that.
"Unfortunately, consumers continue to take supplements and it's hard to turn that ship even in the face of strong evidence from trials," Miller said in an interview.
With files from CBC's Kas Roussy and Amina Zafar