A FIVE-year study conducted by a team of Finnish researchers has found that significantly higher doses of vitamin D do not reduce the incidence of Type 2 diabetes (T2D) in older adults. The findings challenge the belief that increased vitamin D supplementation could play a role in diabetes prevention for individuals with normal glucose metabolism.
The Finnish Vitamin D Trial (FIND), conducted between 2012 and 2018, involved 2,495 participants (men aged 60 and older and women aged 65 and older). Participants were randomly assigned to receive either a placebo, 40 micrograms of vitamin D3 per day, or 80 micrograms of vitamin D3 per day. Over the study period, 105 participants developed T2D, with no statistically significant differences observed between the groups: 38 cases in the placebo group, 31 in the 40-microgram group, and 36 in the 80-microgram group.
Low vitamin D levels have previously been associated with a higher risk of T2D in population studies. However, these observational studies could not confirm whether vitamin D supplementation directly reduces the risk of the disease. While some experimental studies suggested that high doses of vitamin D might slightly lower the risk of developing diabetes in individuals with prediabetes, there has been limited research on its long-term effects on individuals without impaired glucose metabolism until now.
The FIND study excluded 224 participants who were already using diabetes medications. Comprehensive lifestyle, nutrition, and health data were collected from participants, supplemented by information from national health registers. Detailed examinations, including blood samples, were conducted on a subgroup of 505 participants.
At the start of the trial, the average blood calcidiol level, a marker of vitamin D status, was 75 nmol/l, with only nine per cent of participants classified as having a deficiency (levels below 50 nmol/l). By the end of the first year, calcidiol levels rose to 100 nmol/l in the 40-microgram group and 120 nmol/l in the 80-microgram group, while remaining unchanged in the placebo group. Despite these increases, no differences were found in blood glucose levels, insulin levels, body mass index, or waist circumference among the groups.
The results suggest that higher-than-recommended doses of vitamin D do not significantly affect T2D risk in individuals with normal glucose metabolism and adequate vitamin D levels. However, researchers highlight the need for further studies to explore potential benefits for individuals with vitamin D deficiency.
Victoria Antoniou, EMJ
Reference
Virtanen JK et al. The effect of vitamin D3 supplementation on the incidence of type 2 diabetes in healthy older adults not at high risk for diabetes (FIND): a randomised controlled trial. Diabetologia. 2024;DOI:10.1007/s00125-024-06336-9.
