Vitamin D is in many ways essential to the body, and low vitamin D levels have been connected to a wide range of diseases such as cancer, skeletal diseases, infections and cardiovascular diseases.
Epidemiological studies have long shown that diabetics often have also low blood levels of vitamin D, which is why low vitamin D levels have been suspected of causing a risk for developing diabetes. However, reasons for the low blood levels of vitamin D in patients with diabetes have been unknown, and academic literature contains some conflicting information on this topic.
In a study recently published in the Diabetes journal, researchers describe a new, previously unknown mechanism that regulates the bioactivation of vitamin D in the body.
"Our research strongly suggests that low vitamin D levels are more likely the result than the cause of diabetes," says Jukka Hakkola, Professor of Pharmacology at the University of Oulu.
In healthy people, vitamin D that is formed in the skin or obtained from nutrition is converted in the liver to calcidiol (vitamin 25-OH-D), which is regarded as a storage form of vitamin D. According to the current understanding, the concentration of calcidiol reflects the intake and levels of vitamin D in the body. In fact, it is precisely the blood concentration of calcidiol that is measured when vitamin D levels are tested.
The study showed that due to a mechanism activated in both type 1 and type 2 diabetes, the conversion of vitamin D into calcidiol was prevented. In patients with diabetes, the formation of calcidiol may be prevented on a long-term basis, resulting in a vitamin D deficiency. It is possible that patients with diabetes are less able to utilise vitamin D that is produced in their skin or obtained from nutrition.
It was also found in the same study that fasting, too, prevents the formation of calcidiol, but the significance of this phenomenon is still unclear.
The study utilised modern cell techniques and animal models, and the clinical applicability of the phenomenon must be ensured with follow-up studies. If the results can be confirmed in humans, Hakkola says that there may be cause to alter the vitamin D intake recommendations for patients with diabetes.
The study was led by the University of Oulu and carried out in co-operation with researchers from Germany, the US and the University of Eastern Finland. Business partners from Oulu were also involved in the project. In Finland, the study has been funded by the Academy of Finland and the Diabetes Research Foundation.
Article: Aatsinki SM, Elkhwanky MS, Kummu O, Karpale M, Buler M, Viitala P, Rinne V, Mutikainen M, Tavi P, Franko A, Wiesner RJ, Chambers KT, Finck BN, Hakkola J. Fasting-Induced Transcription Factors Repress Vitamin D Bioactivation, a Mechanism for Vitamin D Deficiency in Diabetes. Diabetes 2019 Mar. (Epub ahead of print)
Professor of Pharmacology
University of Oulu
Research Unit of Biomedicine
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Last updated: 9.4.2019