Vitamin D tests conducted on a group of University of Toronto students have found that virtually all non-whites had insufficient levels of the sunshine vitamin, putting them at elevated risk of debilitating diseases such as osteoporosis, cancer and diabetes.
The research, which is awaiting publication in a medical journal, found that 100 per cent of those of African origin were short of vitamin D, as were 93 per cent of South Asians (those of Indian or Pakistani origin), and 85 per cent of East Asians (those of Chinese, Indochinese or Filipino origin, among other countries).
The findings have alarmed the researchers, who say that if the results are typical of Canada's growing non-white population, the country could be facing a public health crisis.
"I think it's important to take measures as soon as possible for this," said Esteban Parra, an anthropologist at the university who worked on the study and said the result "really surprised" researchers.
Insufficient vitamin D amounts were also found among those of European ancestry, but were less widespread, at 34 per cent of those surveyed.
The research, based on blood tests conducted at the university's Mississauga campus in February and March, is the first to systematically examine vitamin D levels of a group of racially diverse, young Canadian adults and categorize the results by ethnicity.
A variety of factors influence how much of the vitamin people have, but skin colour and diet are among the most important.
The results indicate that Canada may have to revise its vitamin D intake levels and increase awareness about the risk of deficiencies, particularly among non-whites.
Some of the levels found - among people from all ethnic groups - were so low that if the students had been infants, they would have been at risk of the debilitating childhood bone disease known as rickets. Insufficiency in the study was defined as a blood level of less than 50 nanomoles/litre, or about half the amount found earlier this year to prevent cancer in a U.S. trial.
Currently, Health Canada doesn't have a racially based recommendation for vitamin D, and tells everyone to take the same amount. It didn't respond to requests for its reaction to the study, but said earlier this year that it was interested in reviewing the country's vitamin D recommendations.
The Canadian Cancer Society, however, earlier this year advised non-whites that they need to consume more than whites. The recommendation, through diet and supplements: 1,000 IU a day year-round for non-whites, and that amount in fall and winter for whites.
The new study vindicates the cancer society's approach, and also suggests that the country's main food-fortification strategy - adding vitamin D to milk and infant formula - doesn't work for non-whites as they get older, although it helps prevent rickets during infancy.
The idea of adding the nutrient to milk was adopted when the population was mainly of Northern European origin, the group most likely to drink the dairy product over a full lifetime and least likely to have allergies to it.
The U of T findings reinforced the importance of skin colour, which has been known for more than a decade to be a factor determining how easily a person is able to make vitamin D at a given latitude.
Most of a person's vitamin D is made when skin is exposed to strong spring and summer ultraviolet light, hence its nickname the sunshine vitamin. Those with darker skins have more pigmentation due to melanin, a natural sunscreen, that slows the ability of skin to make the vitamin.
"The darker your skin, the lower your average vitamin D level will be. There is no doubt about it," said Reinhold Vieth, a professor in the department of nutritional sciences at the university and another of the researchers. Dr. Vieth said Canada needs a public health strategy that includes more information about vitamin D, particularly for those at risk of deficiencies based on skin colour.
One of the participants in the study, Roselle Gonsalves, said she was "very much surprised" that her vitamin reading, while near the average of the group, was considered insufficient, even though she had a summer job working outdoors for part of the day. Ms. Gonsalves, of South Asian ancestry, hadn't been aware that melanin in skin reduced vitamin D levels, and before participating in the study had thought her skin colour gave her an advantage when it came to the nutrient. "I was shocked," she said.
Regardless of racial background, people living in Canada are among those at the highest risk in the world for vitamin D insufficiency because of the country's northern latitude. It is impossible, even in southern parts of Canada, to make the vitamin in skin for about six months each year during the fall and winter because the sunlight is too feeble, so the amount a person is able to build up during the summer is of critical importance.
The study took samples from 107 healthy young adults who self-reported their ancestry. Those participating were also asked to keep a diary of everything they ate and all the supplements they took for a week, to determine how much of the nutrient they are consuming.
Even among those whose diet log indicated they were complying with Health Canada's daily recommended intake of 200 IU, Dr. Parra said many students still had insufficient levels of the nutrient, suggesting the national standard is too low.
THE SUNSHINE VITAMIN Most of the vitamin D circulating in our bodies is made in our skin, when it is exposed to ultraviolet light.
Whites can make about 10,000 International Units after about 10 minutes to 15 minutes in a bathing suit around noon in summer. Those with darker skin need up to six times longer to make the same amount because their higher levels of melanin act like a natural sunscreen.
Those with low levels can easily correct the problem by taking supplements. Most multivitamins contain 400 IU, but vitamin D pills have up to 1,000 IU. A year's supply of the bigger dose costs about $15 to $20, or about five cents a day.
There are a number of conflicting recommendations on how much vitamin D to take. Health Canada developed its recommendations 10 years ago, and many critics say its advice is outdated. In any case, the agency says an adequate amount for those aged one to 50 is 200 IU daily; for 51 to 70 it is 400 IU, and over 70 it is 600 IU. The safe upper limit is 2,000 IU.
Given that differences in skin colour determine how much vitamin D a person makes in sunlight, the Canadian Cancer Society is recommending non-whites take 1,000 IU daily year-round, while whites take that amount only in fall and winter.
Government health-insurance plans cover blood tests for vitamin D requested by physicians. Many researchers think people need at least 75 nanomoles/litre for optimum health, although typical levels in Canada in winter fall to around 40 nmol/L, and even less in non-whites.
Vitamin D insufficiency used to be thought of as a problem causing only rickets, but in recent years, researchers have found that low levels of the nutrient are linked to a disparate range of diseases and health problems, including many types of cancer, osteoporosis, mult-iple sclerosis, diabetes and susceptibility to tuberculosis and influenza.
Diet is a source of vitamin D, but very few foods contain it naturally. In Canada, milk and some other products are artificially fortified: a cup of milk contains about 100 IU. Oily fish, such as salmon and sardines,
also contain about 300 IU a serving. Smaller amounts are found in organ meat and egg yoke.
MAN-MADE VITAMIN D
With the right amount of exposure to UV-B sunlight, it's possible for humans to create enough vitamin D. Here's how:
- Sebaceous glands Produce an oily substance thatcontains acompound called 7-dehydrocholesterol.
- Sunlight Provides the energy needed for 7-dehydrocholesterol to rearrange itself into a chemical called previtamin D3.
- Key organs The liver and kidney convert the previtamin D3 to vitamin D. From there, it is released into the general circulation and transported to target organs. As people age, the concentration of 7-dehydrocholesterol falls, reducing their ability to produce vitamin D.
Sources: University of Toronto, Scientific American, American Society for Nutrition