Role of vitamin D in prevention of type 2 diabetes mellitus: A systematic review and meta-analysis

The escalating prevalence of diabetes mellitus, projected to affect over 700 million by 2045, underscores the urgent need for effective management and prevention strategies, with type 2 diabetes mellitus (T2DM) constituting over 90% of these cases globally. The present meta-analysis aims to rigorously evaluate the potential of vitamin D supplementation in mitigating the onset of T2DM, amidst the backdrop of its biological plausibility yet inconclusive evidence regarding its efficacy in reducing new incidences of the disease. A comprehensive literature search up to December 2023 in MEDLINE, EMBASE and the Cochrane Library, employing a strategy focused on diabetes and vitamin D, identified randomized controlled trials (RCTs) that explore the impact of vitamin D supplementation on T2DM onset in adults with impaired glucose regulation, incorporating quality assessment via the Cochrane ROB2 tool and utilizing meta-analysis with RevMan Web to evaluate effect magnitude and heterogeneity. In a meta-analysis of 11 RCTs with 5,221 prediabetic patients, vitamin D supplementation was associated with a 10% reduction in the progression to T2DM [RR, 0.90; 95% CI, (0.81-0.99)] and a significant increase in regression to normoglycemia [RR, 1.24; 95% CI, (1.08-1.43)], with no significant heterogeneity or publication bias observed. This meta-analysis of 11 RCTs shows that vitamin D supplementation in prediabetic patients lowers the risk of T2DM and promotes regression to normoglycemia, with no significant differences in subgroup analyses or interaction with baseline vitamin D levels, ethnicity, or body mass index (BMI). Despite indications from some trials that baseline vitamin D status may influence outcomes, the present comprehensive analysis found benefits of vitamin D across diverse populations, including non-obese individuals, without conclusive evidence linking supplementation to changes in BMI or age-specific advantages.