Genetically low vitamin D concentrations and myopic refractive error: a Mendelian randomization study.

Area of Science:

• Ophthalmology
• Genetics
• Nutritional Science

Background:

• Myopia prevalence has risen globally, with outdoor time implicated.
• Observational studies suggest a link between low vitamin D [25(OH)D] and myopia.
• Distinguishing vitamin D's effect from outdoor time in observational studies is challenging.

Purpose of the Study:

• To investigate if genetically determined vitamin D levels influence the degree of myopia using Mendelian randomization.
• To clarify the independent contribution of vitamin D to refractive error.

Main Methods:

• Mendelian randomization (MR) analysis was performed.
• Utilized genome-wide association study (GWAS) data from the Consortium for Refractive Error And Myopia (CREAM).
• Employed single nucleotide polymorphisms (SNPs) in vitamin D-related genes (DHCR7, CYP2R1, GC, CYP24A1) as instrumental variables.

Main Results:

• The effect of vitamin D on refractive error was -0.02 D (95% CI -0.09, 0.04) per 10 nmol/l increase in Caucasians.
• In Asians, the effect was 0.01 D (95% CI -0.17, 0.19) per 10 nmol/l increase.
• Confidence intervals indicate a very small, statistically insignificant contribution of vitamin D to myopia.

Conclusions:

• Genetically determined vitamin D levels have a minimal, indistinguishable-from-zero effect on myopia.
• Observational study findings linking vitamin D to myopia are likely confounded by time spent outdoors.
• This MR study provides robust evidence against a causal role of vitamin D in myopia development.