May offer explanation for less type 2 diabetes in white population.
As serum levels of 25-hydroxyvitamin D increase, the risk of diabetes decreases in non-Hispanic whites and Mexican Americans, but not seen in blacks.
In the December issue of Diabetes Care, Dr. Robert Scragg, from the University of Auckland in New Zealand, and colleagues note that the findings may "offer an explanation, in part, for the generally lower prevalence of type 2 diabetes observed in Caucasian populations around the world compared with other ethnicities."
The results are based on a study of 6228 subjects who participated in the Third National Health and Nutrition Examination Survey (NHANES III). They provided a sample representative of the US population.
The risk of diabetes fell in non-Hispanic whites and Mexican Americans as vitamin D levels rose. Compared to those with lowest levels (43.9 nmol/L or less), whites with the highest levels (at least 81.0 nmol/L) had an odds ratio for diabetes of 0.25. For Mexican Americans, the corresponding ratio was 0.17.
The reason why no inverse association was seen in blacks is unclear, but the researchers believe it may "reflect decreased sensitivity to vitamin D and/or related hormones" in this ethnic group.
The team calls for further research to confirm the findings and to pinpoint underlying mechanisms, but point out that simple and cheap strategies to increase vitamin D levels are readily available.
Diabetes Care 2004;27:2813-2818.