Vitamin D3 Supplementation Improved Cognitive Function in Diabetic Elderly Patients with Good Glycemic Control in Japan: A Pilot Study

Background: We studied the effects of vitamin D3 supplementation on serum levels of glycosylated hemoglobin, 25-hydroxyvitamin D and 1, 25-hydroxyvitamin D, and on cognitive function in elderly diabetic patients. Methods: We enrolled 6 male and 9 female Japanese patients (age: 74.4 ± 6.2) with controlled diabetes mellitus who attended an outpatient clinic. The serum glycosylated hemoglobin, 25-hydroxy vitamin D, and 1, 25-hydroxy vitamin D concentrations were measured prior to supplementation and after 3, 9 and 12 months of supplementation with vitamin D3 (500 IU/day of vitamin D3, corresponding to twice the daily requirement). The Montreal Cognitive Assessment-Japanese version was used for the cognitive function test. Data were analyzed using a two-way ANOVA or the Friedman test followed by a Bartlett analysis for homoscedasticity. Results: The results showed that before vitamin D3 supplementation 25-hydroxy vitamin D level was < 20ng/ mL (deficient) in all patients except one (insufficient). Our results show that individual 25-hydroxy vitamin D levels vary significantly from each other and by supplementation duration. The vitamin D deficient group decreased from 14 to 8 patients (5: became insufficient, 1: became sufficient) and the insufficient group decreased from 1 to 0patients after 9 months. The 1, 25-hydroxyvitamin D and glycosylated hemoglobin levels did not vary significantly with duration of supplementation. The Montreal Cognitive Assessment- Japanese version scores did not vary significantly from each other or by supplementation duration. However, we observed increased Montreal Cognitive Assessment-Japanese version scores after supplementation in 60% of the patients. Conclusion: These findings show that vitamin D supplementation is associated with improved serum vitamin D levels and might improve cognitive function.