High-Dose Vitamin D Supplementation Shows Minimal Effect on Type 2 Diabetes Risk in Healthy Older Adults

Low levels of vitamin D have been linked with a higher risk of developing type 2 diabetes; however, limited research is available on whether vitamin D supplements can reduce the possibility of acquiring the disease. New study findings from the University of Eastern Finland assessed the use of higher doses of vitamin D in relation to the incidence of type 2 diabetes in healthy older adults, finding minimal effect.¹

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Many individuals experience vitamin D deficiency as their diet does not meet The Institutes of Medicine’s recommended dose of 600 international units (IU) of vitamin D per day.² On average, an individual receives around 168 to 204 IU of vitamin D daily from food intake, according to the 2015–2016 National Health and Nutrition Examination Survey.³

“Effects of vitamin D supplementation on glucose metabolism are plausible, because the physiologically active form of vitamin D, 1,25-dihydroxyvitamin D (1,25(OH)₂D), is directly involved in the regulation of glucose metabolism by improving islet functioning and reducing insulin resistance,” wrote the authors of the study, in a news release.⁴

Previously conducted experimental studies have displayed that the intake of significantly higher doses of vitamin D slightly reduces the risk of developing type 2 diabetes in individuals with impaired glucose metabolism (prediabetes). However, the study authors noted that no effects have been demonstrated among individuals without prediabetes.¹

The researchers conducted a double-blind, placebo-controlled Finnish Vitamin D, randomized controlled trial which extended from 2012 to 2018. The study assessed the use of vitamin D supplemental compared to a placebo in relation to the risk of type 2 diabetes, including a total of 2495 generally healthy older individuals. Men participants were aged 60 years and older and women aged 65 years and older.^1,4

The individuals were categorized into 3 groups and were randomly assigned to receive either a placebo, 40 micrograms of vitamin D₃ per day, or 80 micrograms of vitamin D₃ per day. The study authors noted that the prespecified primary and secondary outcomes were occurrence of cardiovascular disease and cancer, along with the incidence of type 2 diabetes as a prespecified tertiary outcome.^1,4

The researchers also included a subcohort group of 505 individuals, closely monitoring available blood samples to evaluate blood calcidoil levels, which describes the body’s vitamin D status to further identify the incidence of type 2 diabetes.^1,4

Throughout the 5-year study period, the results demonstrated that 105 individuals developed type 2 diabetes, with 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. The results did not display a significant difference in the number of cases between the 3 groups.^1,4

In the subcohort analyses, the average blood calcidiol level was 75 nanomoles per liter (nmol/L) at the start, apart from levels below 50 nmol/l among 9% of individuals. In a 12-month follow-up the average calcoidiol level was 100 nmol/l in the 40-microgram vitamin D group and 120 nmol/l in the 80-microgram vitamin D group, with no significant change among the placebo group.¹

The subcohort analyses also assessed the effects of vitamin D on blood glucose, insulin levels, body mass index, and waist circumference during the first 2 years of the study, but no differences were observed between the 3 groups, according to study authors.¹

The findings suggest that higher doses of vitamin D than recommended does not significantly impact the risk of developing type 2 diabetes among individuals without prediabetes who already have tolerable vitamin D status. However, the study authors noted that the results do not exclude the influence of high-dose vitamin D supplementation among vitamin D–deficient populations with an average risk for type 2 diabetes.^1,4

REFERENCES

1. Taking high-dose vitamin D supplements for five years did not affect the incidence of type 2 diabetes. EurekAlert. News release. December 3, 2024. Accessed December 9, 2024. https://www.eurekalert.org/news-releases/1066890.

2. Vitamin D supplements may lower blood pressure in older people with obesity. News release. EurekAlert!. November 12, 2024. Accessed December 9, 2024. https://www.eurekalert.org/news-releases/1063997.

3. Vitamin D. National Institutes of Health. July 26, 2024. Accessed December 9, 2024. https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/.

4. 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 randomized controlled trial. Springer Nature Link. News release. December 2, 2024. Accessed December 9, 2024. https://link.springer.com/article/10.1007/s00125-024-06336-9.