What Do You Need to Know About Vitamin D and Diabetes?
Laura Hollar, MD, and Kim A. Carmichael, MD—Series Editor
Hollar L, Carmichael KA. The link between vitamin D and diabetes. Consultant. 2018;58(5):e163.
Q. How can a patient with diabetes be screened for vitamin D deficiency?
A. Vitamin D status is a global concern among persons with diabetes. The prevalence of vitamin D deficiency in the United States is approximately 40%, with higher rates among persons with darker skin, poor health status, and lower education levels.1 Screening can be performed with a simple serum test of the 25-hydroxyvitamin D (25OHD) level, which is used a biomarker for vitamin D status. Vitamin D deficiency is defined as a serum 25OHD level of less than or equal to 20 ng/mL and vitamin D insufficiency as less than or equal to 30 ng/mL. Among persons with diabetes, screening for vitamin D deficiency is of particular importance to identify reversible risk factors for poor glycemic control and other general comorbidities.
Q. Does vitamin D play a role in modifying the risk of developing diabetes?
A. The evidence for vitamin D as a modifiable risk factor for diabetes is growing. Many cross-sectional and prospective observational studies have shown that there is a lower risk of developing type 2 diabetes with increasing 25OHD levels.2 In one meta-analysis of 21 studies enrolling a total of 76,000 participants, those in the highest tertile of 25OHD level had a 38% lower risk of developing type 2 diabetes compared with those in the lowest tertile.3 The meta-analysis also showed that a 4-ng/mL increment in the 25OHD level correlated with a 4% lower risk of type 2 diabetes.3 The potential positive effect of vitamin D supplementation seems to be more prominent in persons who are at high risk of developing diabetes, such as those with prediabetes.
Q. Does vitamin D supplementation affect glycemic control in patients with diabetes?
A. An adequate vitamin D level seems to improve glycemic control in persons with diabetes. One study of 3,393 Australian adults found that every 4 ng/mL increment in the serum 25OHD level significantly improved the fasting plasma glucose level and the hemoglobin A1c level.4 This association was present after adjustments for social, dietary, and metabolic syndrome components (eg, waist circumference, hypertension, cholesterol level). However, vitamin D supplementation does not appear to improve glycemic status in persons with diabetes with either vitamin D insufficiency or sufficiency.5
Several mechanisms have been proposed for the influence of vitamin D on diabetes risk and control. The positive effect of vitamin D on diabetes is likely related to beta cell function and insulin activity. Vitamin D receptor is expressed in pancreatic beta cells, and vitamin D deficiency impairs glucose-mediated insulin secretion via these receptors. Regulation of extracellular calcium concentration by vitamin D also affects the pancreatic beta cells, since insulin secretion is a calcium-dependent process. The biologically active form of vitamin D, 1,25-dihydroxyvitamin D, appears to stimulate expression of insulin receptors and thus affects insulin sensitivity.2 The role of vitamin D in attenuating systemic inflammation has been proposed as having a positive influence on diabetes, as well.2
Q. What is the association between vitamin D and cardiovascular risk in persons with diabetes?
A. In a general population, a low 25OHD level predicted cardiovascular disease and all-cause mortality. An inverse association between 25OHD level and the risk of cardiovascular morbidity and mortality exists among the population with diabetes. One prospective study showed that an 8 ng/mL increase in 25OHD was associated with 37% decrease in cardiovascular disease risk, a finding that remained significant after adjustment for hemoglobin A1c level.6
Laura Hollar, MD, is a clinical fellow in the Department of Medicine, Division of Endocrinology, Metabolism and Lipid Research, at Washington University School of Medicine in St Louis, Missouri.
Kim A. Carmichael, MD, is an associate professor of medicine in the Department of Medicine, Division of Endocrinology, Metabolism and Lipid Research, at Washington University School of Medicine in St Louis, Missouri. He discloses that he is on the speakers bureau for Janssen, which may be relevant to the content of this article.
- Forrest KY, Stuhldreher WL. Prevalence and correlates of vitamin D deficiency in US adults. Nutr Res. 2011;31(1):48-54.
- Mitri J, Pittas AG. Vitamin D and diabetes. Endocrinol Metab Clin North Am. 2014;43(1):205-232.
- Song Y, Wang L, Pittas AG, et al. Blood 25-hydroxy vitamin D levels and incident type 2 diabetes: a meta-analysis of prospective studies. Diabetes Care. 2013;36(5):1422-1428.
- Pannu PK, Piers LS, Soares MJ, Zhao Y, Ansari Z. Vitamin D status is inversely associated with markers of risk for type 2 diabetes: a population based study in Victoria, Australia. PLoS One. 2017;12(6):e0178825.
- Wu C, Qiu S, Zhu X, Li L. Vitamin D supplementation and glycemic control in type 2 diabetes patients: a systematic review and meta-analysis. Metabolism. 2017;73:67-76.
- Samefors M, Scragg R, Länne T, Nyström FH, Östgren CJ. Association between serum 25(OH)D3 and cardiovascular morbidity and mortality in people with type 2 diabetes: a community-based cohort study. Diabet Med. 2017;34(3):372-379.