Could a Vitamin Hold the Key to Improving Insulin Sensitivity?
Beyond its well-known role in bone health, vitamin D has gained attention for its potential impact on glucose metabolism and insulin resistance. Vitamin D is a fat-soluble vitamin, but it acts more like a hormone, helping regulate calcium and phosphorus balance, modulating immune function, cell differentiation and inflammation, and influencing whole-body insulin sensitivity.
An inverse relationship has been observed between vitamin D status and markers of inflammation, insulin resistance, and glucose intolerance. An estimated 41% of the U.S. population has vitamin D insufficiency, with even higher prevalence during winter months and among women, non-Hispanic Black Americans, and older adults.1 Low vitamin D levels have been associated with an increased risk of developing type 2 diabetes2 and macrovascular and microvascular complications in individuals with type 2 diabetes. These risks spark interest in whether vitamin D supplementation could play a role in preventing and managing diabetes.
Mechanisms Linking Vitamin D and Insulin Resistance
Vitamin D receptors (VDRs) are located in pancreatic β-cells, adipose tissue, and skeletal muscle, which are all key sites in glucose metabolism. Adequate vitamin D levels support insulin secretion, enhance tissue sensitivity to insulin, reduce the expression of proinflammatory cytokines, and regulate metabolic pathways that influence insulin resistance. These physiological mechanisms explain how vitamin D status might influence the development and progression of type 2 diabetes.
Conflicting Evidence from Clinical Research
Recent studies have sought to clarify whether vitamin D supplementation can improve insulin sensitivity. A 2023 meta-analysis published in Scientific Reports analyzed 18 randomized controlled trials and 20 observational studies involving over 12,000 participants.3 It found that vitamin D supplementation was associated with significant reductions in fasting insulin, glucose levels, and HOMA-IR scores, suggesting improved insulin sensitivity. Their reviewed observational studies, however, suggested that improvements were not independent of other variables.
Overall, their findings concluded individuals with low levels may benefit from supplementation.
However, a 2020 meta-analysis of 18 randomized control trials, published in Diabetes Care,4 found no significant improvements in insulin sensitivity using gold-standard measures such as the hyperinsulinemic-euglycemic clamp, the Matsuda index, or intravenous glucose tolerance tests.
They concluded there was no evidence that Vitamin D supplementation benefited individuals with or at risk of insulin resistance.
Differences in study populations, vitamin D dosing amounts, baseline vitamin D status, and outcome measures likely account for outcome differences between the two meta-analysis reports.
Vita D Clinical Guidelines: Conflicting Recommendations
Clinical recommendations vary regarding vitamin D supplementation for diabetes prevention. The 2024 Endocrine Society Clinical Practice Guidelines (endorsed by AACE) provide updated supplementation guidance.5 But the American Diabetes Association took a different stance.
2024 Endocrine Society Clinical Practice Guidelines
For healthy adults the guidelines recommend adhering to the Institute of Medicine’s RDAs: 600 IU (15 μg) daily for ages 18-50 and 800 IU for ages 50-74. The guidelines also identify groups such as older adults (over 75), youth (under 18), pregnant individuals, and people with prediabetes who may benefit from higher intakes and supplementation. They suggested empiric Vitamin D supplementation in individuals with prediabetes to reduce the risk of progression to diabetes, but they did not name a specific recommended dose. They noted that optimal Vitamin D intake and serum 25 (OH)D concentration for disease prevention were uncertain and did not suggest routine screening.5 The guideline referenced the reviewed clinical trial dosing of 842 – 7543 IU daily. However, these recommendations are cautious and emphasize daily over high-dose intermittent supplementation. Supplementation guidelines for individuals with diabetes were not reviewed.
In contrast, the American Diabetes Association (ADA) Standards do not recommend vitamin D supplementation solely for the prevention of type 2 diabetes.6 While some studies suggest a potential link between vitamin D deficiency and an increased risk of developing diabetes, ADA states that more research is needed to confirm a causal relationship and to determine whether vitamin D supplementation can effectively delay or prevent the onset of diabetes.
Implications for Practice
For diabetes educators, these findings highlight the importance of individualized care and the need for thoughtful evaluation of vitamin D status in people with or at risk for diabetes. While vitamin D supplementation may not be universally recommended for improving insulin sensitivity or preventing diabetes, supplementation can be considered in high-risk groups to support potential health benefits. Until we have conclusive recommendations, educators can remain up to date with emerging research and tailor care strategies to an individual’s health status, risk, lifestyle, and curiosity about Vitamin D supplementation.
References:
- 1. Cui A, Xiao P, Ma Y, Fan Z, Zhou F, Zheng J, Zhang L. Prevalence, trend, and predictor analyses of vitamin D deficiency in the US population, 2001-2018. Front Nutr. 2022 Oct 3;9:965376
- Adriyan Pramono, Johan W.E. Jocken, Ellen E. Blaak, Marleen A. van Baak; The Effect of Vitamin D Supplementation on Insulin Sensitivity: A Systematic Review and Meta-analysis. Diabetes Care1 July 2020; 43 (7): 1659–1669.
- Lei X, Zhou Q, Wang Y, et al. Serum and supplemental vitamin D levels and insulin resistance in T2DM populations: a meta-analysis and systematic review. Sci Rep. 2023;13(1):12343
- Pramono A, Jocken JWE, Blaak EE, van Baak MA. The Effect of Vitamin D Supplementation on Insulin Sensitivity: A Systematic Review and Meta-analysis. Diabetes Care. 2020 Jul;43(7):1659-1669.
- Marie B Demay, Anastassios G Pittas, Daniel D Bikle, Dima L Diab, Mairead E Kiely, Marise Lazaretti-Castro, Paul Lips, Deborah M Mitchell, M Hassan Murad, Shelley Powers, Sudhaker D Rao, Robert Scragg, John A Tayek, Amy M Valent, Judith M E Walsh, Christopher R McCartney, Vitamin D for the Prevention of Disease: An Endocrine Society Clinical Practice Guideline, The Journal of Clinical Endocrinology & Metabolism, Volume 109, Issue 8, August 2024, Pages 1907–1947
- Vitamins, Minerals and Supplements downloaded on April 19th 2025 from https://diabetes.org/food-nutrition/diabetes-vitamins-supplements.
Join us for this upcoming Level 5 Course
Level 5 | Weight-Inclusive Diabetes Care: Turning Compassion into Practical Tools
This session provides healthcare providers with actionable strategies to integrate weight-inclusive care into diabetes management practices, focusing on improving outcomes through respect for body diversity and individual autonomy. Weight stigma is a well-documented barrier to effective care, contributing to poorer glycemic control, disordered eating, and care avoidance. By shifting from a weight-focused approach to one aligned with Health at Every Size (HAES®), providers can foster trust, enhance participant engagement, and support sustainable health behaviors.
Jessica Jones, MS, RD, CDCES, will share evidence-based insights on mitigating weight stigma and applying HAES-aligned strategies in practice. Participants will learn how to build rapport, set realistic nutrition goals, and implement interventions that prioritize blood sugar management, joyful movement, and intuitive eating. This session equips providers with tools to deliver compassionate, person-centered care, improving both clinical outcomes and the provider-participant relationship.
![](/wp-content/uploads/2023/01/insta-png-v5.png")
