Relationship between vitamin D deficiency and diabetic retinopathy: a meta-analysis

Abstract

Objective

The purpose of this study was to evaluate the evidence for an association between diabetic retinopathy (DR) and vitamin D deficiency.

Design

Meta-analysis.

Methods

We included 14 observational studies with 10 007 participants who had undergone assessment for both DR and vitamin D deficiency. Pooled odds ratios (ORs) and 95% CIs were calculated using a random-effect, Mantel–Haenszel analysis.

Results

There was a statistically significant association between DR and vitamin D deficiency with an overall pooled OR of 1.27 (95% CI, 1.17–1.37; P = 0.001; I² = 80%; P_{heterogeneity} = 0.01). There was also a statistically significant lower serum vitamin D level in patient subgroups with DR versus control groups, with an overall mean difference of –1.32 ng/mL (95% CI, –2.50 to –0.15; P = 0.001; I² = 89%; P_{heterogeneity} = 0.01).

Conclusion

There is a statistically significant association between vitamin D deficiency and DR.

RÉSUMÉ

Objet

Vérifier l’existence d’un lien entre la rétinopathie diabétique et la carence en vitamine D.

Méthodes

On a procédé à la méta-analyse de 14 études d’observation réunissant 10 007 participants soumis à un dépistage de la rétinopathie diabétique et d’une carence en vitamine D. Les rapports de cotes (RC) et les intervalles de confiance (IC) à 95 % groupés ont été calculés au moyen d’un modèle à effets aléatoires de Mantel-Haenszel.

Résultats

Il existe une corrélation statistiquement significative entre la carence en vitamine D et la rétinopathie diabétique, les RC groupés s’établissant à 1,27 (IC à 95 %: 1,17 à 1,37; p = 0,001; I² = 80 %; valeur de p pour l’hétérogénéité = 0,01). Par ailleurs, le taux sérique de vitamine D était significativement inférieur sur le plan statistique dans les sous-groupes atteints de rétinopathie diabétique que dans les groupes témoins, l’écart moyen global s’inscrivant à -1,32 ng/mL (IC à 95 %: -2,50 à -0,15; p = 0,001; I² = 89 %; valeur de p pour l’hétérogénéité = 0,01).

Conclusions

Il existe bel et bien une corrélation statistiquement significative entre la carence en vitamine D et la rétinopathie diabétique.

Introduction

Diabetic retinopathy (DR) is one of the leading causes of blindness worldwide and is the leading cause of blindness for individuals aged 20 to 64 years in the United States.¹ It is thought that at 20 years after diabetes onset, nearly all patients with diabetes Type I and >60% of those with diabetes Type II will have evidence of DR on examination.² DR, characterized as a neurovascular disease entity, results from hyperglycemia-induced changes to the blood–retinal barrier and retinal vasculature. The disease initially presents as a nonneovascular form, or nonproliferative diabetic retinopathy (NPDR). Increasing damage to the retinal vasculature results in vessel leakage and diabetic macular edema, and subsequent vascular sclerosis results in ischemia, angiogenesis, and, eventually, retinal neovascularization, or proliferative diabetic retinopathy (PDR).¹

Animal studies have suggested that supplementation of calcitriol [1,25(OH)₂D], the hormonally active metabolite of vitamin D, is protective against retinal neovascularization and multiple other studies have documented the antiangiogenic effects of vitamin D, albeit primarily in tumor models.³ Vitamin D deficiency (VDD), defined as a serum 25-hydroxyvitamin D [25(OH)D)] concentration <20 ng/mL, also has been associated with impairment of insulin secretion, metabolic syndrome, and systemic diabetic progression.4, 5 Because vitamin D metabolism is in part dependent on sunlight, VDD follows a seasonal cycle, with vitamin D levels lower in the winter than in the summer.⁴

There are a number of observational studies6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 in the English-language literature that yield competing conclusions regarding the association between VDD and DR. The primary objective of this meta-analysis was to comprehensively determine the strength of association between VDD and DR. The secondary objective of this study was to determine if there exists any significant difference in serum vitamin D levels between patients with DR and control group patients.