An epidemiological study has linked a deficiency in vitamin D to an increased risk of diabetes.
Researchers from the University of California San Diego School of Medicine (CA, USA) and Seoul National University (South Korea) performed an epidemiological study on a cohort of 903 adults, with an average age of 74, which linked the level of vitamin D in their blood to an increased risk of diabetes. The cohort was free of diabetes in 1997–1999. The study, published in PLoS One, followed the patients through 2009.
Previous studies have suggested that a higher plasma concentration of 25-hydrocyvitamin D is associated with a lower risk of pre-diabetes or diabetes. However, until now there has been no large-scale epidemiological study of at-risk age groups to test this hypothesis.
Prior to the study, the scientists established the healthy concentration of 25-hydrocyvitamin D as 30ng/ml. Controversially this concentration is 10ng/ml more than the current level recommended by the US government.
Through 2009 the researchers performed diagnostic diabetic tests on the cohort including fasting plasma glucose and oral glucose tolerance. They also measured the blood plasma concentration of 25-hydroxyvitamin D and considered any patient with a concentration below 30ng/ml to be deficient.
Author Sue Park sums up the results:
"We found that participants with blood levels of 25-hydroxyvitamin D that were above 30ng/ml had one-third of the risk of diabetes and those with levels above 50 ng/ml had one-fifth of the risk of developing diabetes."
However, the authors are reticent to read too much into the results. Co-author Cedric Garland has studied vitamin D’s association with disease using epidemiological studies since the 1980s. He cautions that cause and effect is not proven, only an association:
“Further research is needed on whether high 25-hydroxyvitamin D levels might prevent type 2 diabetes or the transition from pre-diabetes to diabetes. But this paper and past research indicate there is a strong association.”
Garland suggests that dietary supplements or more sun exposure could raise vitamin D levels to above 30ng/ml. He hopes that if further studies establish causal links between vitamin D deficiencies and diabetes, then the US government should raise its current recommend daily amount of vitamin D.