The most comprehensive survey ever undertaken on vitamin D in Canadians has found widespread deficiencies of the sunshine vitamin, which is being promoted for everything from the prevention of cancer to reducing heart attack risk.
The survey, conducted by Statistics Canada, found that two-thirds of the population has vitamin D levels below the amounts research is associating with reduced risk of chronic diseases such as cancer, while one in 10, or more than three million people, have such low readings that they don't have enough for good bone health. About 4 per cent have so little that they're at risk for rickets, a debilitating childhood bone disease.
Statscan also found a huge vitamin D disparity among Canadians based on racial origin, with whites having substantially higher concentrations than the prevailing levels in the country's growing non-white population. Whites had an average of nearly 40 per cent more of the nutrient than non-whites.
It termed low levels of the vitamin a "worldwide problem," and said most Canadians don't have concentrations at "the level proposed for optimal health."
It said some of the biggest factors in low vitamin D readings were being non-white and consuming a smaller amount of milk, which is fortified with the vitamin.
Gerry Schwalfenberg, an assistant clinical professor in the department of family medicine at the University of Alberta, said testing showing that "60 to 70 per cent [of Canadians] have inadequate levels [is] not good," given that vitamin D insufficiency is being linked to so many chronic diseases
The research from the Statscan, conducted as part of a broad analysis of the health of Canadians, is likely to add to the controversy over the adequacy of current advice on the amount of Vitamin D people need to consume each day.
Health Canada, in conjunction with U.S. government agencies, set a recommended daily intake in 1997 based on the relatively low amounts needed for good bone development. The new data indicate that a substantial number of Canadians aren't getting enough even for this purpose, let alone the far higher levels suggested for the prevention of chronic diseases.
The recommendation also doesn't differ based on skin type, one of the most important determinants of vitamin D levels. People make most of the nutrient circulating in their bodies themselves, in bare skin exposed to strong summer light – hence the sunshine nickname. Non-whites make less because their skins have more pigmentation, a natural sunscreen.
Health Canada is reviewing whether its advice needs to be revised, but the results aren't expected until this summer.
In the meantime, many doctors and some public health groups, such as the Canadian Cancer Society, have been advising people to take larger amounts as a precaution, although Health Canada doesn't endorse this and some medical professionals worry that vitamin D is being overhyped and say its possible benefits need to be further confirmed in drug-style clinical trials.
Statscan deemed readings of 75 nanomoles/litre or more as optimal, based on research showing people with amounts below this threshold appear to be at increased risk for breast cancer, colorectal cancer, heart disease and multiple sclerosis, among other ailments. A nanomole per litre is a count of vitamin D molecules in a litre of blood. But the agency also cautioned that there is scientific uncertainty about this figure, as did Health Canada in a statement.
"There is currently a lack of consensus on the levels considered to be associated with adequacy, inadequacy and deficiency," Health Canada said.
The average white person had 71 nmol/L, modestly under the purported optimum threshold, while non-whites were far lower, at 52 nmol/L, Statscan found.
Researcher Kellie Langlois said the sampling wasn't extensive enough to discover whether there was a difference among South Asian, black and Chinese Canadians, or whether non-whites were disproportionately found among those at risk for rickets or poor bone health.
The low levels in people of non-European ancestry worry researchers.
Reinhold Vieth, professor of nutrition at the University of Toronto, said people with readings below 50 nmol/L may have so little of the nutrient that their bodies will scavenge calcium from bones to meet other metabolic needs.
Health Canada says Canadians should take from 200 to 600 International Units of vitamin D a day for good bone health. A cup of fortified milk contains about 100 I.U., while a typical multivitamin has 400. But some researchers say this amount is woefully inadequate. Dr. Schwalfenberg says vitamin D's anti-cancer benefit "probably begins at 90 nmol/L. That would require at least 3,000 I.U. a day to achieve."
Vitamin D is needed to properly absorb calcium and phosphorous, but nearly every cell has receptors for it, and it is involved in the proper functioning of hundreds of genes.
Statistics Canada tested the vitamin D in blood from about 5,300 people aged 6 to 79, a sample group it said was representative of the vast majority of Canadians. About half of 1 per cent had readings over 220 nmol/L, indicating high sun exposure, high use of supplements or tanning lights. No one had levels above the 375 nmol/L considered potentially toxic.