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Abstract

Background: Myopia prevalence has increased in the past 20 years, with many studies linking the increase to reduced time spent outdoors. A number of recent observational studies have shown an inverse association between vitamin D [25(OH)D] serum levels and myopia. However, in such studies it is difficult to separate the effects of time outdoors and vitamin D levels. In this work we use Mendelian randomization (MR) to assess if genetically determined 25(OH)D levels contribute to the degree of myopia.Methods: We performed MR using results from a meta-analysis of refractive error (RE) genome-wide association study (GWAS) that included 37 382 and 8 376 adult participants of European and Asian ancestry, respectively, published by the Consortium for Refractive Error And Myopia (CREAM). We used single nucleotide polymorphisms (SNPs) in the DHCR7 , CYP2R1, GC and CYP24A1 genes with known effects on 25(OH)D concentration as instrumental variables (IV). We estimated the effect of 25(OH)D on myopia level using a Wald-type ratio estimator based on the effect estimates from the CREAM GWAS.Results: Using the combined effect attributed to the four SNPs, the estimate for the effect of 25(OH)D on refractive error was -0.02 [95% confidence interval (CI) -0.09, 0.04] dioptres (D) per 10 nmol/l increase in 25(OH)D concentration in Caucasians and 0.01 (95% CI -0.17, 0.19) D per 10 nmol/l increase in Asians.Conclusions: The tight confidence intervals on our estimates suggest the true contribution of vitamin D levels to degree of myopia is very small and indistinguishable from zero. Previous findings from observational studies linking vitamin D levels to myopia were likely attributable to the effects of confounding by time spent outdoors.

Item Type:	Article
Authors/Creators:	Cuellar-Partida, G and Williams, KM and Yazar, S and Guggenheim, JA and Hewitt, AW and Williams, C and Wang, JJ and Kho, PF and Saw, SM and Cheng, CY and Wong, TY and Aung, T and Young, TL and Tideman, JWL and Jonas, JB and Mitchell, P and Wojciechowski, R and Stambolian, D and Hysi, P and Hammond, CJ and Mackey, DA and Lucas, RM and MacGregor, S
Keywords:	Mendelian randomization, myopia, vitamin D
Journal or Publication Title:	International Journal of Epidemiology
Publisher:	Oxford Univ Press
ISSN:	0300-5771
DOI / ID Number:	https://doi.org/10.1093/ije/dyx068
Copyright Information:	Copyright The Author 2017; all rights reserved.
Related URLs:	Google Scholar: Hewitt, AW UTAS Profile: Hewitt, AW
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