The Finnish Vitamin D Trial (FIND) aimed to evaluate the impact of vitamin D3 supplementation on the incidence of type 2 diabetes in healthy older adults. This 5-year randomized, placebo-controlled trial included 2271 participants aged 60 or older who were free from cardiovascular disease and cancer and not using diabetes medications. Participants were randomly assigned to one of three groups: placebo, 1600 IU/day vitamin D3, or 3200 IU/day vitamin D3. The study found no significant difference in the incidence of type 2 diabetes between the placebo and vitamin D3 supplementation groups. The hazard ratios for diabetes incidence were 0.81 for the 1600 IU/day group and 0.92 for the 3200 IU/day group compared to placebo, with no trend observed (p-trend=0.73). 

Further analysis revealed that vitamin D3 supplementation had varying effects depending on participants’ BMI. Those with a BMI under 25 kg/m² showed a significantly lower risk of developing diabetes with vitamin D3 supplementation, while no significant effects were seen in those with higher BMI. In a subgroup with more detailed follow-up, no significant changes were observed in plasma glucose, insulin levels, or other metabolic markers. The trial concluded that for generally healthy older adults with sufficient serum vitamin D3 levels for bone health, vitamin D3 supplementation did not significantly reduce the risk of developing type 2 diabetes. 

Reference: Virtanen JK, Hantunen S, Kallio N, 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 Dec 2. doi: 10.1007/s00125-024-06336-9. Epub ahead of print. PMID: 39621103