High Vitamin D Doses Don’t Prevent Type 2 Diabetes

According to a new study by the University of Eastern Finland, taking significantly higher doses of vitamin D than recommended for five years did not affect the incidence of type 2 diabetes in elderly men and women.

In population studies, low levels of vitamin D in the body have been associated with a higher risk of type 2 diabetes. However, such observational studies cannot directly conclude whether taking vitamin D supplements can reduce the risk of developing the disease. Experimental studies have shown that taking significantly higher doses of vitamin D than recommended slightly reduces the risk of developing type 2 diabetes in individuals with impaired glucose metabolism, i.e., those with prediabetes.

In contrast, no effects have been observed in individuals without prediabetes. However, studies on non-prediabetic subjects have either used relatively small doses of vitamin D or have been short-term. Until now, there has been no research data on the effects of long-term use of high doses of vitamin D on the risk of type 2 diabetes in individuals without glucose metabolism disorders.

During the Finnish Vitamin D Trial (FIND) conducted by the University of Eastern Finland from 2012 to 2018, 2,495 men aged 60 and older and women aged 65 and older were randomly assigned to either a placebo group or groups receiving either 40 or 80 micrograms of vitamin D3 per day for five years. In the statistical analyses of the now-published sub-study, 224 participants who were already using diabetes medications at the start of the study were excluded. Comprehensive information was collected from the participants regarding their lifestyle, nutrition, diseases, and risk factors. Data was also obtained from national health registers. Approximately one-fifth of the participants were randomly selected for more detailed examinations, and blood samples were taken from them.

During the five years, 105 participants developed type 2 diabetes: 38 in the placebo group, 31 in the group receiving 40 micrograms of vitamin D3 per day, and 36 in the group receiving 80 micrograms of vitamin D3 per day. There was no statistically significant difference in the number of cases among the groups.

In the group of 505 participants who were studied in more detail, the blood calcidiol level, which reflects the body’s vitamin D status, was on average 75 nmol/L at the start, and only 9% had a low level, i.e., below 50 nmol/L. After one year, the calcidiol level was on average 100 nmol/L in the group taking 40 micrograms of vitamin D per day and 120 nmol/L in the group taking 80 micrograms of vitamin D per day. There was no significant change in the placebo group. The effects of vitamin D on blood glucose and insulin levels, body mass index, and waist circumference were examined during the first two years of the study, but no differences were observed among the groups.

The findings of the FIND study reinforce the view that taking higher doses of vitamin D than recommended does not significantly affect the risk of developing type 2 diabetes in individuals without prediabetes and who already have a good vitamin D status. So far, there has been no research data on whether high doses of vitamin D can be beneficial in preventing type 2 diabetes in individuals without prediabetes but with vitamin D deficiency.

The study was funded by the Research Council of Finland, the University of Eastern Finland, the Juho Vainio Foundation, the Finnish Foundation for Cardiovascular Research, the Diabetes Research Foundation, the Finnish Cultural Foundation, and the Medicinska Understödsföreningen Liv och Hälsa.

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