Vitamin D is required for bone development and maintenance of strong bones and teeth, but recent studies suggest that it also plays an important role in non-bone disorders such as diabetes. A study, published in Diabetes Care, looked at the association of vitamin D and hemoglobin A1c (HbA1c), which measures long term blood sugar control. The researchers found a strong association between low levels of vitamin D and high values of HbA1c. High HbA1c values indicate poor blood sugar control.
HbA1c and vitamin D
When the concentration of blood sugar (glucose) is high for an extended period of time, glucose starts to attach to proteins in the blood. The HbA1c test measures the amount of glucose attached to the hemoglobin protein. The test is generally used to measure diabetes status and how well diabetics are controlling their blood sugar. An HbA1c of 6 percent or less is normal. For diabetics, the goal is to reduce their HbA1c to below 7 percent. Because numerous studies have indicated a link between blood vitamin D levels and type 2 diabetes, researchers looked at the relationship of HbA1c with vitamin D. They analyzed the data from the 2003 to 2006 National Health and Nutrition Examination Survey on 9773 U.S. adults. They took into account diabetes treatment of individuals and the changes in vitamin D and A1c levels with age. The researchers found an inverse relationship between vitamin D and A1c in people 35 to 74 years of age. An inverse relationship means that when vitamin D was elevated, A1c was low, but when vitamin D was low, A1c was high. In the people, who were treated for diabetes, the relationship was not as clear as in untreated individuals. The researchers conclude: “These findings support a mechanistic link between serum vitamin D concentrations, glucose homeostasis, and the evolution of diabetes in a large segment of the U.S. adult population” (Kositsawat, J. et al.).
Vitamin D and diabetes
In another study, researchers at Tuft’s University, Boston, Massachusetts, analyzed the vitamin D status of 1972 people, who were part of the Framingham study. Initially, none of the participants had type 2 diabetes, but after seven years of follow-up, 133 people became diabetic. The people with the lowest vitamin D levels had the greatest incidence of diabetes. The researchers conclude in their report, published in the Journal of Clinical Nutrition in 2010, that vitamin D status is inversely associated with type 2 diabetes risk.
In yet another study at John Hopkins, researchers evaluated medical data of 124 patients with type 2 diabetes, who came in for treatment between 2003 and 2008. Even while getting treated, 91 percent of patients, either had vitamin D deficiency (less than 15 ng per ml) or vitamin D insufficiency (15 to 30 ng per ml). Again, researchers found an inverse relationship between vitamin D and HbA1c levels.
Preventing type 2 diabetes
Screening non-diabetic people for either vitamin D or HbA1c may identify individuals at risk for type 2 diabetes. The studies suggest that if you take vitamin D supplements or get sufficient sunshine exposure, you could prevent both vitamin D deficiency and the development of diabetes. So far, no studies have been done to test whether taking vitamin D supplements can prevent or reverse diabetes.
Kositsawat, J. et al. Association of A1C levels with vitamin D status in U.S. adults: data from the National Health and Nutrition Examination Survey. Diabetes Care (2010) 33: 1236