Do Vitamin D levels affect diagnosis and progression of type 2 diabetes?

There has been a rise in type 2 diabetes prevalence over the past decades, which is estimated to continue. As a part of the efforts to improve the treatment and prevention of T2DM, there has been an increasing interest in examining risk factors as potential targets for intervention; vitamin D is one such risk factor.

Metabolism of vitamin D takes place in the liver; it is converted to (25(OH)D) and then metabolized further in the kidneys to 1,25-dihydroxyvitamin D (1,25(OH)2D), the biologically active form. Vitamin D status is based mainly on the 25(OH)D concentration owing to its longer half-life. The primary function of vitamin D is the regulation of phosphate and calcium levels in bone metabolism. Still, it may also be involved in beta cell protection, blood sugar control, and insulin resistance and secretion; the receptors for vitamin D are present in pancreatic beta cells and insulin's target tissues, such as the adipose tissue, liver, and skeletal muscle.

Against the above background, Giovanni Allaoui, University Hospital of North – Norway, Tromsø, Norway, and colleagues aimed to assess the association between pre- and post-diagnostic 25(OH)D concentrations and type 2 diabetes over 30 years in patients who developed T2DM versus the healthy controls in a case-control study.

The study included 254 patients whose blood samples were collected at five different time points (T1–T5). The study consisted of 254 participants, out of which 116 were diagnosed with type 2 diabetes between T3 and T4 and were taken as cases, and the rest 138 were controls. The pre-and post-diagnostic changes in 25(OH)D concentrations were examined, and the associations between these concentrations and T2DM at each time point were also examined using logistic regression.

The study reported the following findings:

• 25(OH)D concentrations at different time points, and the longitudinal change concentrations varied between cases and controls and by sex.
• Each 5-nmol/l rise in 25(OH)D concentrations for women was inversely linked with type 2 diabetes at T3 (odds-ratio, OR, 0.79); however, for men, this same rise was positively associated with T2DM at T1 (OR 1.12).
• Cases showed a significant decrease in pre-diagnostic 25(OH)D concentrations and a considerable increase in post-diagnostic 25(OH)D concentrations.
• Each increase in 1-unit in month-specific z-score change between T1 and T3 was remarkably inversely associated with T2DM (OR 0.52 for men, OR 0.51 for women), and each increase between T3 and T5 was remarkably positively linked with T2DM in women (OR 2.48).

"This is the first observational study with repeated pre-and post-diagnostic concentrations of 25(OH)D in type 2 diabetes cases and controls over 30 years," the researchers wrote. "Our findings indicate an association between changes in concentration of 25(OH)D concentrations and T2DM."

Reference:

Allaoui, G., Rylander, C., Fuskevåg, OM. et al. Longitudinal changes in vitamin D concentrations and the association with type 2 diabetes mellitus: the Tromsø Study. Acta Diabetol (2022). https://doi.org/10.1007/s00592-022-02001-y