Objective To conduct a systematic review and meta-analysis of the association of blood vitamin D (25-hydroxyvitamin D, 25(OH)D) concentration and vitamin D pathway genes with myopia.
Methods We searched the MEDLINE and EMBASE databases for studies published up to 29 January 2018. Cross-sectional or cohort studies which evaluated the blood 25(OH)D concentration, blood 25(OH)D3 concentration or vitamin D pathway genes, in relation to risk of myopia or refractive errors were included. Standard mean difference (SMD) of blood 25(OH)D concentrations between the myopia and non-myopia groups was calculated. The associations of blood 25(OH)D concentrations and polymorphisms in vitamin D pathway genes with myopia using summary ORs were evaluated.
Results We summarised seven studies involving 25 008 individuals in the meta-analysis. The myopia group had lower 25(OH)D concentration than the non-myopia group (SMD=−0.27 nmol/L, p=0.001). In the full analysis, the risk of myopia was inversely associated with blood 25(OH)D concentration after adjusting for sunlight exposure or time spent outdoors (adjusted odds ratio (AOR)=0.92 per 10 nmol/L, p<0.0001). However, the association was not statistically significant for the <18 years subgroup (AOR=0.91 per 10 nmol/L, p=0.13) and was significant only for 25(OH)D3 (likely to be mainly sunlight derived), but not total 25(OH)D (AOR=0.93 per 10 nmol/L, p=0.00007; AOR=0.91 per 10 nmol/L, p=0.15). We analysed four single nucleotide polymorphisms in the VDR gene from two studies; there was no significant association with myopia.
Conclusions Lower 25(OH)D is associated with increased risk of myopia; the lack of a genetic association suggests that 25(OH)D level may be acting as a proxy for time outdoors.
- optics and refraction
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Contributors SMT conceived the study design and did the data collection, data analysis and data interpretation. She wrote the main manuscript text and prepared the tables and figures. TL did the data collection and data interpretation. SSR did the data collection and data analysis. SY provided some raw data and critically revised the manuscript. LJC, DAM, RML, CPP critically revised the manuscript. JCY conceived the study design, supervised the data collection and data analysis and critically revised the manuscript.
Funding This study was supported in part by the General Research Fund (GRF), Research Grants Council, Hong Kong (14111515 (JCY)); the Direct Grants of the Chinese University of Hong Kong (4054197 (CPP), 4054193 (LJC) and 4054121 & 4054199 (JCY)); the UBS Optimus Foundation Grant 8984 (JCY) and the CUHK Jockey Club Children Eye Care Programme. RML is supported by a National Health and Medical Research Council of Australia Senior Research Fellowship.
Competing interests None declared.
Patient consent Next of kin consent obtained.
Provenance and peer review Not commissioned; externally peer reviewed.