Vitamin D Fails to Prevent Type 2 Diabetes

Japanese researchers have completed a 3-year-long randomized trial designed to assess the effects of vitamin D on the prevention of type 2 diabetes in people at high risk of the condition. A total of 1256 individuals were included in this study.

Prediabetes is a condition in which fasting blood sugar levels are higher than normal, but not high enough to be diagnosed as diabetes. According to the American Diabetes Association (ADA), blood glucose levels between 5.6 to 6.9 mmol/L and HbA1c (glycated hemoglobin) levels between 5.7 to 6.4% are considered prediabetes. Patients with these readings have an increased risk of developing type 2 diabetes.

It is estimated that 350 million people are living with prediabetes in the world. Besides, they are more likely to develop type 2 diabetes and cardiovascular disease. Fortunately, following a healthy dietary pattern and participating in regular physical activity may help to delay the development of the disease. However, not all patients have the opportunity to maintain a healthy lifestyle in the long term. Thus, scientists are exploring other approaches to prevent type 2 diabetes.

Overview of the Trial on the Effect of Vitamin D on Prevention of Diabetes Worked

Tetsuya Kawahara and colleagues from Japan's University of Occupational and Environmental Health carried out a double-blind, randomized, placebo-controlled study to investigate whether taking 0.75 micrograms of eldecalcitol (an active vitamin D3 derivative) per day could reduce the incidence of type 2 diabetes in people with prediabetes. The study involved 1256 people aged 30 years and older. 630 participants received a daily dose of eldecalcitol, while 626 other study participants received a placebo.

Study Results

Сlinical study found no significant association between daily vitamin D supplementation with the prevention of type 2 diabetes in pre-diabetic Japanese individuals.

Data from the three-year follow-up period showed that 79 (12.5%) of 630 participants in the eldecalcitol group and 89 (14.2%) of 626 in the placebo group developed type 2 diabetes. Treatment with eldecalcitol decreased the risk of the condition by 13%, but the results were not statistically significant (p = 0.39).

However, the researchers decided to re-assess the findings of the study after adjusting for patients’ background parameters.

• age
• sex
• high blood pressure
• body mass index
• family history of diabetes
• initial hemoglobin A1c level
• plasma glucose concentration in fasting state and after a 75-gram oral glucose tolerance test
• vitamin D levels in the blood

As a result, daily intake of vitamin D showed a beneficial effect on one of the indicators. Patients who took vitamin D experienced a considerable decline in blood glucose concentration 30 minutes after a 75 g oral glucose load compared to baseline glucose level. This represents a 31% reduction in the risk of developing type 2 diabetes (p = 0.02) in this group of participants.

Researchers observed no significant differences between the groups in other variables, such as glycated hemoglobin or body mass index.

Unfortunately, this study has shown conflicting results about the effect of vitamin D on the prevention of type 2 diabetes in people with prediabetes. The efficacy of this method found after adjustment for multiple factors has to be proved in large-scale (large sample size) trials.

The material was prepared using the data from The BMJ.