The cause of juvenile diabetes has long eluded medical researchers, with no one knowing why children develop the disease, and why rates vary so dramatically around the world.
Among children under 14, Canadians are believed to have the third-highest rate in the world. A youngster growing up in Finland is about 400 times more likely to develop the lifelong ailment involving insulin deficiency than one growing up in Venezuela.
But U.S. researchers believe they have a plausible explanation for the medical puzzle: They suspect the odds of acquiring the disease are linked to latitude and the way it determines how much vitamin D children produce from exposure to sunlight.
In a groundbreaking paper published today in the online version of the journal Diabetologia, researchers from the University of California, San Diego, found that the incidence of diabetes tends to be low at or near the equator, where the rate often approaches zero, and then rises steadily at progressively higher latitudes, reaching peaks in places like Canada, Finland and southern Argentina's Tierra del Fuego.
At higher latitudes, sunshine is too feeble for much of the year to allow children to produce vitamin D the natural way, through exposure of skin to strong ultraviolet light, increasing the odds of them developing juvenile diabetes, the paper says.
The researchers contend that the link to the so-called sunshine vitamin opens up a promising avenue to reduce rates of juvenile diabetes, for which doctors have no prevention strategy.
“This suggests there is a tremendous amount of room for reduction in the incidence of type 1 diabetes with vitamin D,” says Cedric Garland, professor of family and preventive medicine at the University of California, San Diego, and the paper's lead author.
Dr. Garland said it may be possible to reduce the risk of the disease by giving children about 1,000 to 2,000 international units of vitamin D daily, or less in sunny locations or during the summer. That dose would give children in northern countries vitamin D levels similar to those of people in tropical locations.
This “would revolutionize, I think, pediatric preventive medicine practice by allowing the doctors to ensure adequate vitamin D status and prevent a terrible, lifelong disease,” Dr. Garland said.
The possible link to vitamin D is “a very exciting hypothesis and if it's true, a major dent could be made in the number of children … developing type 1 diabetes every year,” agreed Shayne Taback, a pediatric endocrinologist and diabetes researcher at the University of Manitoba.
The amounts of vitamin D that Dr. Garland suggests are far higher than what Health Canada recommends – 400 IU a day for breast-fed infants under 1 and 200 IU for older children. Health Canada's maximum safe dose is 1,000 IU a day for those younger than 1 and 2,000 for those older, although the government agency said last month that it intends to review its recommendations in light of new research linking insufficiency of the vitamin to a number of diseases.
Health Canada said in an e-mail response to questions from The Globe that it recommends Canadians follow its existing doses pending the outcome of the review.
The Canadian Diabetes Association has been financing research into vitamin D, including a study by Dr. Taback that gave infants 400 IU or 2,000 IU daily to see whether there were any adverse effects. None were found.
Some researchers are cautious about the new paper because it amounts to the scientific equivalent of circumstantial evidence. The differing incidence by latitude could be due to some other factor, such as genetics.
Dr. Taback leads a team that wants to conduct a drug-style clinical study to determine whether that the nutrient actually can prevent diabetes. Type 1 Diabetes TrialNet, an international consortium that oversees research on the disease, has approved his proposed study, which is awaiting funding and would use doses as high as 2,000 IU.
As many as 180,000 Canadians have juvenile or type 1 diabetes, according to figures from the Public Health Agency of Canada. It is a chronic, lifelong autoimmune disease, usually diagnosed during childhood and treated by injecting insulin. Among its symptoms are extreme thirst and sudden weight loss.
It is a different illness from the more common adult onset diabetes, known as type 2, which is linked to such modern lifestyle factors as being overweight and sedentary.
The new research is among a number of studies suggesting a link between the vitamin and the disease.
Juvenile diabetes is thought to have a genetic component, with about 15 per cent of the population potentially susceptible, although it is not known what environmental factors trigger a fraction of those to develop the disease, in which the body's immune system turns on itself, destroying cels in the pancreas responsible for insulin production.
