Vitamin D3 Does Not Reduce T2D Risk in Healthy Seniors

TOPLINE:

Long-term daily supplementation with moderate (1600 international units [IU]) or high (3200 IU) doses of vitamin D3 doesn’t reduce the risk for type 2 diabetes (T2D) among generally healthy older adults who have serum vitamin D levels sufficient for bone health.

METHODOLOGY:

• Observational studies have consistently linked low vitamin D levels with an increased risk for T2D, and short-term randomized trials have shown a protective effect of vitamin D supplementation for those with impaired glucose metabolism but not in populations of average risk-taking low doses.
• The Finnish Vitamin D Trial, conducted from 2012 to 2018 in generally healthy men (≥ 60 years) and women (≥ 65 years) without a history of cardiovascular disease or cancer, assessed the effects of 5 years of moderate and high vitamin D3 supplementation on the incidence of major chronic diseases.
• This analysis of T2D incidence included 2271 older participants (mean age, 68.2 years; 43.9% women) without self-reported use of diabetes medications at baseline.
• Participants were randomly assigned to receive placebo (n = 760), 1600 IU/d of vitamin D3 (n = 744), or 3200 IU/d of vitamin D3 (n = 767) and followed for a mean duration of 4.2 years, with T2D incidence assessed by diagnostic code from health registries.
• A representative subcohort of 505 participants underwent detailed investigations including blood sampling at months 0, 6, 12, and 24 for serum 25-hydroxyvitamin D3 [25(OH)D3], plasma glucose, and insulin concentrations.

TAKEAWAY:

• No significant difference in T2D incidence was observed between groups: Placebo (5.0%; 38 people), 1600 IU/d (4.2%; 31 people), and 3200 IU/d (4.7%; 36 people; P = .731 for trend), with no appreciable sex differences.
• When stratified by body mass index (BMI), a lower incidence of T2D with vitamin D supplementation was observed among those with a BMI
• In the subcohort, no significant differences in changes in plasma glucose, insulin concentrations, BMI, or waist circumference with vitamin D3 were observed between the three treatment groups during the 24-month follow-up (P ≥ .19).
• In an analysis excluding T2D from the first 2 years, researchers observed a potentially increased risk for T2D with increasing vitamin D dose (with wide CIs).

IN PRACTICE:

“Our findings do not suggest benefits of long-term moderate- or high-dose vitamin D3 supplementation for incidence of type 2 diabetes or glucose metabolism or body size among generally healthy older vitamin D–sufficient men and women who were not at high risk for type 2 diabetes,” the authors wrote.

SOURCE:

The study was led by Jyrki K. Virtanen, University of Eastern Finland, Institute of Public Health and Clinical Nutrition, Kuopio, Finland, and was published online in Diabetologia.

LIMITATIONS:

The study relied on national health registries to collect data on incident T2D events, which may have led to some T2D cases being missed. Data on serum 25(OH)D3 concentrations were available for the subcohort only, which prevented the investigation of whether vitamin D–deficient participants would have benefited from supplementation. The study was not specifically designed or powered for diabetes prevention, and information on participants’ diabetes history at baseline was not available. Wide CIs suggest uncertainty around some of the findings. Study participants were White and older, so caution is needed in generalizing results to groups of other ages, races and ethnicities, and different vitamin D levels.

DISCLOSURES:

The study received funding from the Academy of Finland, University of Eastern Finland, Juho Vainio Foundation, and other sources. Some authors reported receiving grants or travel support from pharmaceutical companies and certain institutions.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.