And a new study examining type 1 diabetes rates in specific populations confirms that rates are lower in sunny equatorial countries and higher in northern latitude countries that get far less sunlight.
UVB and Type 1 Diabetes
Skin exposure to ultraviolet B (UVB) through sunlight is a major source of vitamin D, and it has long been recognized that type 1 diabetes rates tend to be greater in higher latitude countries where there is little sunlight, like Finland and Sweden, and lower in countries that are close to the equator.
The observation led to the speculation that vitamin D plays a major role in type 1 diabetes risk, longtime vitamin D researcher Cedric F. Garland, DrPH, tells WebMD.
In an effort to test the theory, Garland and colleagues from the Moores Cancer Center at the University of California, San Diego, examined type 1 diabetes rates worldwide in 51 regions while attempting to control for confounding factors such as the level of medical care.
They confirmed that incidence rates were generally highest in high latitude regions, independent of per capita health expenditures.
"One theory is that high levels of health care in (high latitude) Scandinavian countries may explain the higher diagnosis rates," Garland says. "But Cuba also has very good health care, and we saw very low rates there."
In Finland, for example, about 37 out of 100,000 boys under the age of 14 develop type 1 diabetes. In Cuba, the rate is closer to 2 in 100,000.
The study appears in the June 4 online issue of the journal Diabetologia.
Vitamin D Supplementation
The researchers conclude that their findings are compelling enough to recommend vitamin D supplementation for all babies and young children.
Garland says children over the age of 1 can take up to 1,000 international units (IU) of vitamin D a day, if approved by their pediatrician. Younger children should take no more than 400 IU a day.
American Diabetes Association Vice President of Clinical Affairs Sue Kirkman, MD, considers the recommendation premature.
"It is a bit of a leap at this point to conclude that vitamin D supplementation can prevent type 1 diabetes," she tells WebMD. "We always have to be careful when we recommend interventions to prevent disease, and this is certainly no exception."
But Kirkman adds that possible vitamin D-diabetes connection deserves further study.
"There is growing evidence about the potential benefits of vitamin D or the harm that is caused from not getting enough of it," she says.
What's the Right Dose?
In the research analysis, published in the June issue of the journal Archives of Diseases in Childhood, investigators combined the results of five studies that examined vitamin D supplementation and type 1 diabetes risk.
They concluded that vitamin D supplementation during infancy is associated with a reduced risk for type 1 diabetes later in childhood.
Supplementation of more than 400 IU a day is not generally recommended for infants and young children.
Lead researcher Christos Zipitis, MD, tells WebMD that it appears that higher levels of vitamin D may be more protective, but he adds that this must be confirmed in future studies.
Zipitis is a pediatrician with the Stockport NHS Foundation Trust in the United Kingdom.
"I think our efforts should concentrate on getting as many babies supplemented as possible rather than worrying too much about the absolute dose," he says. "At the moment, in the U.K., despite official advice, only a tiny minority of babies are supplemented."