Vitamin D and Type 1 Diabetes, Revisited
Several of my patients have asked me about this recent posting on TheAtlantic.com: “We Had Been Giving Our Daughter Vitamin D, Would She Still Have Developed Diabetes?” by Katie Bacon.
In this post, the author questions whether Vitamin D administration would have prevented her daughter from developing Type 1 Diabetes. We have discussed the possible association between Type 1 diabetes and Vitamin D. In her posting, Ms. Bacon mentions the recent paper by Gorham, ED, Garland CF, Burgi, AA et. al., in Diabetololgia (2012) 55:3224-3227, “Lower prediagnostic serum 25-hydroxy vitamin D concentration is associated with higher risk of insulin requiring diabetes: a nested case -controlled study.” The authors proposed that low serum 25-hydroxy Vitamin D concentration might increase the risk of insulin dependant diabetes.
The authors performed a nested case-control study using serum collected from military service members during 2002-2008.
What is a nested case controlled study? It is a variation of the typical case-controlled study where only a subset of controls from the cohort (or group) are compared to the incident cases (those that develop type 1 diabetes). In this type of study, some control members are chosen for each case from that case’s matched risk set.
Of the above cohort, 1000 military service members developed type 1 diabetes. A healthy control was matched to each case on blood draw date, age, sex, and length of service.
What were the results?
According to the authors “individuals with lower 25 hydroxy vitamin D concentrations had a higher risk of developing type 1 diabetes than those with higher concentrations. A 3.5 fold lower risk was associated with a 25 hydroxy vitamin D level concentration greater than or equal to 60 nmol/l or 24 ng/ml.” The results were statistically significant (P<0.001).
What are the limitations of this study?
- Only 1 serum sample was used.
- There may be an association of higher BMI and higher risk of type 1 diabetes, but obesity is only a modest risk factor for type 1 diabetes in children and adolescents. BMI values were present in this particular database. (However, according to the authors all military personnel are required to have a BMI below the usual criterion for obesity (greater than 30 kg/m2).
- The results were based only on this cohort and to generalize for the entire U.S. population may not be appropriate, as patients were not examined for the purposes of this particular study.
Take Home Message
The above study is correlational in nature and does not necessarily prove that Vitamin D deficiency causes Type 1 diabetes; rather there appears to be an association. However, it has been noted that Vitamin D is an immune modulator – hence the association does indeed make biological sense. Much research is currently underway in regard to the association of Vitamin D and diabetes (both type 1 and type 2). Keep in mind that the development of type 1 diabetes requires a certain genetic susceptibility in the HLA locus on chromosome 6 and that something in the environment (viruses etc.) may trigger the development of autoimmunity in which the islet cells are attacked by their own Killer T cells. The role of Vitamin D in this process remains undetermined. However, I do not think it is unreasonable to obtain 25-hydroxy Vitamin D levels as a routine practice in all children due to the minimal exposure to sunlight. In families that have a child with type 1 diabetes, I certainly would consider obtaining a Vitamin D level and if low (<30 ng/ml), I would consider Vitamin D supplements based on your healthcare provider’s recommendations.