How Does Vitamin D Affect Diabetes?

Vitamin D is a fat-soluble vitamin known to play an important role in regulating calcium metabolism and bone health.¹ Vitamin D can be found in fish oils, but is also unique from other vitamins in that humans can synthesize it with adequate exposure to sunlight. The most common manifestation of deficiency is rickets (lack of mineralization of bone) in children.

Despite the understanding that the role of vitamin D is restricted to bone health, studies indicate that it also plays a critical role in endocrine function and in the prevention of type 2 diabetes mellitus (T2DM).² Epidemiological as well as clinical studies show that vitamin D deficiency is associated with increased risk of T2DM. Recent systematic review and meta-analysis report that although vitamin D supplementation does not affect overall incidence of T2DM in non-diabetic individuals, that vitamin D supplementation can lower risk of T2DM in those with prediabetes. Other studies support this finding. For instance, a randomized, placebo-controlled trial on individuals with high risk of diabetes or new-onset T2DM found that 5,000 IU daily vitamin D supplementation for six months significantly improved peripheral insulin sensitivity and pancreatic b-cell function when compared to placebo.³ Additionally, a recent study on healthy older adults not at risk of T2DM found that vitamin D supplementation did not affect the risk of developing T2DM, showcasing vitamin D’s role in diabetes prevention in high-risk population.⁴

What Are the Current Recommendations? 

Reflecting the latest scientific findings, The Endocrine Society updated its vitamin D clinical guidelines in 2024, 13 years since its last edition.⁵ In addition to making lifestyle changes, the guidelines suggest empiric vitamin D supplementation in adults with high-risk prediabetes to prevent progression to T2DM. Those who meet >2 of the prediabetes clinical criteria (impaired fasting glucose, impaired glucose tolerance, elevated HbA1c) are recommended supplementation.

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