Tuesday, July 9, 2002
By Suzanne Rostler
NEW YORK (Reuters Health) - Canadian adults may be at risk of a vitamin D deficiency and therefore more prone to osteoporosis and fractures, researchers report.
The findings, coupled with those of other recent reports, indicate that the recommended intake of vitamin D should be higher than the current 200 international units (IUs) for adults in Canada and the United States.
However, more research is needed into the health effects of low blood levels of vitamin D, David A. Hanley, the study's lead author, said in an interview.
"We need new studies to carefully assess the potential harm associated with mild vitamin D deficiency. In other words, is the finding of generally low vitamin D levels in a population indicative of increased risk of osteoporotic fracture or other health problems? If so, we need to re-assess our public health recommendations for vitamin D intake," said Hanley, who is from the University of Calgary in Canada.
The investigators collected blood samples every 3 months from 188 Canadian adults aged 27 to 89 who were participating in the Canadian Multicentre Osteoporosis Study. This trial was supported by the Dairy Farmers of Canada, Merck Frosst Canada, Eli Lilly Canada, and Procter and Gamble Pharmaceuticals, among other groups.
Blood levels of vitamin D and hormones that help to synthesize the vitamin were measured, but calcium intake was not assessed.
More than one third of the group had blood levels of vitamin D that fell below optimum levels at least once during the year, but the actual proportion of adults with insufficient blood levels of vitamin D may be even higher. The study relied on a conservative threshold for vitamin D in the blood and was conducted in a city with one of the highest levels of sunlight exposure in Canada.
Not surprisingly, levels of vitamin D were lowest in the winter among all the study participants, the researchers report in the June issue of the Canadian Medical Association Journal. Vitamin D, which helps the body to absorb calcium, is added to milk and is also made by the body when skin is exposed to sunlight.
Regardless of season, blood levels of vitamin D were lowest among elderly adults, who are at higher risk of the brittle-bone disease osteoporosis.
The findings support those of other studies on adults living in countries at higher latitudes, where people may not get enough wintertime sunlight to trigger the conversion of the vitamin D precursor in the skin. However, the researchers caution against generalizing the results to all Canadians, since study participants were predominately white and lived in the same city in western Canada.
The darker a person's skin, the more difficult it is for him or her to obtain adequate vitamin D via sunlight.
SOURCE: Canadian Medical Association Journal 2002;166:1517-1524.
Copyright 2002 Reuters