Trial: Vitamin D Supplementation Yielded No Preventive Benefits in T2D

Findings of a recent randomized controlled trial carried out in Japan concluded vitamin D does not prevent type 2 diabetes (T2D) among adults at high risk of the disease. The results were published in The BMJ.

Global prevalence of diabetes is estimated to increase to 629 million individuals in the year 2040, while data from 2015 show 425 million adults already have the disease and 352 million with impaired glucose tolerance are at risk of developing it.

“Vitamin D receptors have been found in various cell types, including the pancreatic β cells, and active vitamin D is reportedly involved in insulin biosynthesis and secretion,” authors wrote. However, previous research has yielded mixed findings on the benefits or lack thereof regarding vitamin D supplementation and T2D development.

A total of 1256 individuals were included in the prospective Diabetes Prevention with active Vitamin D (DPVD) study. All participants were at least 30 years old and had impaired glucose tolerance determined via a 75 g oral glucose tolerance test and assessment of glycated hemoglobin levels.

Patients were recruited from 3 trial hospitals between June 2013 and August 2015. Six hundred and thirty patients received active vitamin D (eldecalcitol 0.75 μg per day) and 626 received a placebo each day for 3 years.

In addition, “study visits were scheduled at 3-month intervals, with the follow-up period concluding after 3 years.” Just over 45% of the cohort was female and the majority (59.1%) of participants had a family history of T2D. Mean patient age was 61.3 years and no clinically significant differences were seen between the 2 groups at baseline.

Analyses revealed:

• During a median follow-up of 2.9 years, 79 (12.5%) of 630 participants in the eldecalcitol group and 89 (14.2%) of 626 in the placebo group developed T2D (hazard ratio [HR] 0.87; 95% CI, 0.67-1.17; P = .39)
• Regression to normoglycaemia was achieved in 145 (23.0%) of 630 participants in the eldecalcitol group and 126 (20.1%) of 626 in the placebo group (HR 1.15; 95% CI, 0.93-1.41; P = .21)
• After adjustment for confounding factors by multivariable fractional polynomial Cox regression analysis, eldecalcitol significantly lowered the development of diabetes (HR 0.69; 95% CI, 0.51-0.95; P = .020)
• Eldecalcitol showed its beneficial effect among the participants with the lower level of basal insulin secretion (HR 0.41; 95% CI, 0.23-0.71; P = .001)
• During follow-up, bone mineral densities of the lumbar spine and femoral neck and serum osteocalcin concentrations significantly increased with eldecalcitol compared with placebo (all P < .001)
• No significant difference in serious adverse events was observed

Elaborating on the lack of preventive effect of vitamin D on T2D, but an effect seen following adjustment for confounding variables, researchers noted “this discrepancy is a result of lack of statistical power, an unbalanced distribution of 2-hour plasma glucose concentrations between participants in the eldecalcitol and placebo groups, or both.”

Findings may not be generalizable to other ethnicities while different factors such as latitude of living area and occupation can impact serum 25-hydroxyvitamin D concentration. Future studies are warranted to better elucidate the potential for a beneficial effect of active vitamin D treatment on the prevention of T2D after adjustment for confounding factors, authors concluded.

Reference

Kawahara T, Suzuki G, Mizuno S, at al. Effect of active vitamin D treatment on development of type 2 diabetes: DPVD randomised controlled trial in Japanese population. BMJ. Published online May 25, 2022. doi:10.1136/bmj-2021-066222