Wednesday, December 19, 2007

Ethnicity/Skin Color May Link to Vitamin D Deficiency

Canadian researchers are working on a new study which confirms that people of color--those of African and east Asian backgrounds--may be dangerously low in vitamin D. Dr. Esteban Parra and his colleagues at the University of Toronto were surprised by these deficiencies. Their study was conducted last winter through blood tests performed on students of the Mississauga campus at the University of Toronto. The students were 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.

When testing for Vitamin D, 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 at which the bones go soft (commonly called rickets). A level between 25 and 50 nmol/L is considered insufficient; but it is not yet low enough to lead to a deficiency.

Parra and his colleagues found a very high prevalence of insufficiency. Their 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.

The big shock came when it was discovered that the darker the skin of the students, the lower their levels of vitamin D.

Among those of European origin, 34 per cent had insufficient levels of vitamin D. For those from East Asian or Chinese descent, 85 per cent had insufficient levels. The students 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. In this last group, about 43 per cent were considered deficient, with levels below 25 nmol/L.

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 the research team.

"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," said one author.

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.


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