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Canadian study points to ‘D’ deficiency

Sunday, December 30th, 2007

 A study of vitamin D levels in more than 100 University of Toronto students has found a much higher proportion of non-white participants had insufficient levels of the vitamin in their blood compared to white students.

The pilot study, which hasn’t been published in a peer-reviewed medical journal yet, was conducted in February and March at the university’s Mississauga campus.

Jodi Lynn Barta, a postdoctoral fellow in anthropology and one of the co-authors, said the researchers wanted to look at wintertime vitamin D levels. The blood of participants was tested, and dietary intake was studied as well.

All seven students of African origin had insufficient levels of vitamin D, along with 93.5 per cent of 31 South Asians, 85 per cent of the 27 East Asians and 34 per cent of the 32 students of European ancestry, Barta said. There were also some mixed-race participants.

The researchers chose to do the tests in winter because that’s when there are fewer UV-B rays from the sun available to Canadians to actually synthesize vitamin D in our skin.

“So the only way that we’re getting vitamin D intake in the winter is through dietary intake and also through any supplementation,” Barta said in an interview Wednesday.

Oily fish, organ meats, fortified milk and margarine are a few of the dietary sources of vitamin D.

“Vitamin D status was actually linked very closely with dietary intake, as one would imagine, but the other significant finding was that it was also correlated with skin pigmentation levels because we measured the amount of melanin in each of the participants’ skin,” Barta said.

“People who had more melanin tended also to have less vitamin D.”

The researchers also found differences in diet among the groups.

“We found that people who are of European background had the highest daily intake of vitamin D in their diet, and subsequently they also had the highest levels of vitamin D,” Barta said.

Supplementation should be encouraged, she said, noting that the Canadian Cancer Society has suggested that everyone in the winter months should take supplements of 1,000 international units per day.

“Those who are at risk – people with darker skin, people who are older because as you get older your skin actually synthesizes less vitamin D – so all of these groups should be paying extra attention, and really supplementing their diet with vitamin D,” Barta said.

Health Canada currently recommends 200 IUs for adults 19 to 50 years of age. In September, it released a statement saying recommendations by various organizations to boost intake were premature, and a comprehensive review was needed before it would revise its own recommendations.

Various studies have suggested that vitamin D deficiency may be linked to a higher risk of dying from cancer, heart disease and diabetes. However, a large study by the U.S. National Cancer Institute published in October found no sign that vitamin D lowers the overall risk of dying from cancer, although people with more vitamin D in their blood did have a significantly lower risk of death from colorectal cancer.

Dr. Reinhold Vieth, a U of T professor and director of the bone and mineral laboratory at Mount Sinai Hospital, said people should want blood vitamin D levels of 75 nanomoles per litre or higher.

“What students of European ancestry have in the winter in Toronto is 52 nanomoles per litre,” said Vieth, who was involved in the study.

“And whether you’re African or East Asian or Indian sub-continent in your family history, the average level was 35 to 30 nanomoles per litre; in other words, less than half what you would wish it to be.”

Below 50 nanomoles is considered insufficient, Barta said.

Vieth said the study confirms information that was already known about vitamin D and skin color.

People with darker skin should be doing something to increase their vitamin D blood level, he said.

“The level your doctor would diagnose rickets at is 25,” he said. “So there are a lot of people walking around with almost rickets’ level of vitamin D during winter.”

Vieth said the anthropologists studying the U of T students in Mississauga (he conducted another portion of the study on an additional 80 students at the downtown Toronto campus) plan to continue their study by giving the students vitamin D supplements to see if that makes a difference, and also tracking their vitamin D levels in summer.

— From the Toronto Globe & Mail and canadapress.com


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