Diabetes and Vitamin D: Is There a Connection?
As always, my fellow blogger, Ann Bartlett, keeps me up to date with the latest rumors or information in the diabetes world and pointed me to the following: "GOT MILK" is a campaign that began in California and is now internationally known about the benefits of drinking milk. In this press release, it was noted that the campaign wishes to expand its message to say, "Vitamin D helps fight juvenile diabetes and along with sun exposure could reduce the risk of developing type 1 diabetes."
I went straight to the Diabetologia (2008) 51: 1391-1398 reference noted in the release. The article was written by Mohr, Garland et.al and called "The association between ultraviolet B irradiance, vitamin D status and, incidence rates of type 1 diabetes in 51 regions worldwide." Indeed, the information was very thought provoking. The authors of the study analyzed the relationship between ultraviolet B irradiance (the primary source of human Vitamin D) and age-standardized incidence rates of type 1 diabetes in children based on world location. The results of the study noted higher incidence rates in regions with higher latitudes and these rates were statistically significant (p<0.001). The authors concluded that there was an association between low Vitamin D exposure and high incidence rates of type 1 diabetes in children. Most interestingly, incidence levels approached zero in regions with high ultraviolet irradiance (vit D exposure). Thus, does Vitamin D (by ingestion or exposure to ultraviolet irradiance) reduce the risk of type 1 diabetes?
According to the authors, "The low incidence rate of type 1 diabetes in regions close to the equator indicates that there is potential for substantial reduction in incidence rates at higher latitudes." Not surprisingly, the highest incidence of type 1 diabetes was in Finland, Sardinia, Italy, Aberdeen of UK, Prince Edward Island (Canada), Sweden, and Norway. Previous studies unsuccessfully attempted to link milk protein produced by cows in Scandinavia to the etiology for the high incidence of type 1 diabetes. As always, these studies provide epidemiological links to certain diseases but do not necessarily prove that decreased levels of serum 25 hydroxy Vitamin D cause type 1 diabetes. I have noted anecdotally that several of my patients have low serum 25 hydroxy Vitamin D levels after working them up for frequent bone fractures or other issues. Administration of Vit D with resultant normalized levels did not normalize blood sugar. Interestingly enough is that we do know that children/teens/adults are born with the predisposition to develop type 1 diabetes based on the HLA locus (DR/DQ) regions. We also know that there needs to be an environmental trigger that allows for the autoimmune destruction of pancreatic islet cells. Perhaps we should add decreased serum 25 hydroxy Vitamin D levels to the possible list of etiologic insults that may lead to the development of Type 1 Diabetes.
The association of serum concentrations of serum 25 hydroxy Vitamin D also may play a role in the development of Type 2 diabetes. According to an epidemiologic report in the latest issue of Diabetes Care (Volume 33, number 2, February, 2010), Drs. Zhao, Ford, and Li noted that "among American adults without physician-diagnosed diabetes, low concentrations of serum 25 hydroxy Vitamin D were associated with markers of increased insulin resistance." The role of parathyroid hormone in relation to insulin resistance would therefore require further investigation.
Insulin resistance is one of the risk factors noted for the development of type 2 diabetes. Thus, low serum levels of 25 hydroxy Vitamin D may be a predictor (or marker) of increased likelihood of diabetes in this population (adults> 20 years).
How do we interpret this information? Very carefully, with the understanding that these papers are epidemiologic in origin and note associations and linkages, not necessarily the cause of either type 1 or type 2 diabetes. We can, however, incorporate several caveats from this information.
1. Type 1 diabetes is caused by a combination of a genetic predisposition (determined by DR/DQ locus on the HLA region of chromosome 6, plus an environmental insult.
2. Proven environmental insults include viruses (Influenza, Rubella, Coxsakie, Mumps, etc.), certain medications, and "other" factors.
3. Perhaps decreased serum 25 hydroxy vitamin D levels may contribute to other "environmental" putative causes.
4. Once an individual develops Type 1 diabetes, exogenous administration of Vitamin D has not (to my knowledge) been demonstrated to reverse the disease.
5. However, in relatives of those with type 1 diabetes, one might consider obtaining a serum 25 hydroxy vitamin D level. If low, supplementation with oral Vitamin D 3 tablets might not be unreasonable in view of the epidemiologic association of low Vitamin D and type 1 diabetes.
6. Adults might consider checking their 25 hydroxy vitamin D levels, especially if they have other risk factors that may contribute to insulin resistance and thus the possibility of the future development of type 2 diabetes. Should their Vitamin D levels be decreased, starting oral Vitamin D supplementation should be considered.
7. Lastly, please discuss these issues with your personal physician before considering any action, as general suggestions may not be appropriate for your unique situation.
If you're in the DC area, be sure to purchase a ticket to the April 25 game between the Washington Nationals and Los Angeles Dodgers and support children with diabetes!