Skin colour linked to vitamin D deficiency
CTV.ca News Staff
Published Tuesday, December 18, 2007 11:08PM EST
A new study has confirmed that people of colour -- those of African and east Asian background -- may be dangerously low in vitamin D -- so low it surprised researchers.
Esteban Parra of the Department of Anthropology at the University of Toronto conducted his study last winter by testing the blood of students on the Mississauga campus at the University of Toronto from a variety of ethnic backgrounds.
He asked 106 healthy young adults to report their ancestry and to keep a diary of everything they ate and all the supplements they took for a week. He then tested their blood for vitamin D, which are measured in 25-hydroxyvitamin D (25-OHD) levels.
Anything above 75 nanomoles per litre (nmol/L) of 25-OHD is considered optimal. Anything less than 25 nmol/L is considered seriously deficient, a level that would put one at risk of developing rickets, a condition in which the bones grow soft. A level between 25 and 50 nmol/L is considered insufficient but not yet low enough to lead to a deficiency.
His first surprise was just how many of the otherwise healthy students were seriously deficient in vitamin D during the winter months, when the number of daylight hours is shortened and when people are less likely to absorb sunlight through exposed skin.
"We found a very high prevalence of insufficiency," Parra reports.
His second finding was that the darker the skin of the students, the lower their levels of vitamin D.
- Among those of European origin, with lighter skin, 34 per cent had insufficient levels of vitamin D.
- Among those from East Asian or Chinese descent, 85 per cent had insufficient levels.
- Among those from South Asia -- countries such as India -- 93 per cent had insufficient levels.
- And among those of African ancestry, 100 per cent -- everyone tested -- had insufficient levels. And among this group, about 43 per cent were considered deficient, with levels below 25 nmol/L.
The study is awaiting publication in an academic journal.
Parra says that the reason that the darker-skinned students had lower vitamin D levels is that darker skin contains a natural sunblock, making it harder for the skin to produce vitamin D from the sun.
The fact that darker-skinned people are not as able to absorb is not new, but the results startled even Parra.
"I was really surprised, because I know that it would be expected that there was going to be a difference. But I didn't think it was going to be that high," he says.
Many of the students weren't aware they were deficient in vitamin D, even though most reported that they regularly drank vitamin D-fortified milk and dairy products.
"I am someone who makes sure I get a lot of sunlight, making sure I get external exposure every day. I thought I was getting the right amount of vitamin D," says one of the test subjects, Roselle Gonsalves, who is of South Asian ancestry and says she takes a daily multivitamin.
Dr. Reinhold Veith, a nutritional researcher at Mount Sinai Hospital in Toronto says he was impressed with the study.
"The results are really quite surprising because we'd expect young people to be outside more than others, but they're almost shockingly low in vitamin D levels," he says.
"Vitamin D affects lots of aspects of health. I mean there is the bone but also cancer, and even risk of type 2 diabetes. These are not minor items."
A landmark study, released earlier this year, found that a combination of vitamin D3 and calcium had a substantially marked effect on reducing cancer incidence. The four-year study found that women who regularly took vitamin D3 had a 60 per cent reduction in cancer infections compared to a group taking placebos.
Shortly after the release of that study, the Canadian Cancer Society issued a recommendation that Canadians take 1,000 International Units of vitamin D during winter months. It also advised those with darker skin to take 1,000 IU units year-round.
Veith believes those are excellent recommendations.
"I think it is a lot like saving for your retirement, you know: the sooner you start, the better," he says.
"What easier way is there to save for your healthy retirement than to protect yourself when you are younger -- in this case, it is probably taking a vitamin D supplement, something I don't think any university student does."
"It's almost like: 'Why should I worry about smoking? I'm healthy right now, I can keep smoking.' I think the vitamin D story is very much analogous to the smoking story, that it will catch up to you in the end, so you better start doing something about it now."
Parra says he hopes this study will remind Canadians to take their vitamin D supplements, particularly because they are already at risk of deficiencies because of the country's latitude and short summers.
"I think the research in the last decade has been very clear in indicating that vitamin D is very important for ultimate health," he says. "And again, it's not that it is something unachievable, really, to get ultimate levels."
Health Canada currently recommends that Canadians in the 18-to-30-year-old age group consume about 200 IU of vitamin D a day, the amount in two cups of milk. The agency has said that it is interested in reviewing the country's vitamin D recommendations.
"Before Health Canada can issue a revised recommendation concerning vitamin D, a comprehensive review that looks at both benefits and safety needs to be undertaken," it said in June.
With a report from CTV's Avis Favaro and producer Elizabeth St. Philip