Only one of eight ocular disorders analyzed in this study—wet AMD—was found to be associated with vitamin D levels. Photo: Carolyn Majcher, OD, Elaine Petry, OD, and Sweta Das, OD. Click image to enlarge.

Recent research has found associations between vitamin D and certain ocular diseases, including myopia, diabetic retinopathy and age-related macular degeneration (AMD). Exploring these potential connections is crucial in light of the high prevalence of vitamin D deficiency in various populations. Therefore, a recent study analyzed data from more than 740,000 European individuals to help ascertain whether a causative link exists between vitamin D levels and the development of eight common eye disorders.

To accomplish this, the study used a bidirectional and multivariable Mendelian randomization (MR) analysis, which the authors described in their paper as a “statistical approach used to examine causal relationships between exposure factors and outcomes.” It examined genetic variants from the FinnGen dataset, which included myopia, primary open-angle glaucoma, anterior iridocyclitis, senile cataract, diabetic retinopathy, retinal vein occlusion, wet AMD and optic neuritis.

The MR analysis revealed a significant association between high vitamin D levels and an increased risk of wet AMD with a risk ratio of 1.35. This finding persisted even after adjusting for multiple confounders such as type 2 diabetes and lifestyle factors in the multivariable MR analysis, which presented an adjusted odds ratio of 1.86.

Contrary to some previous studies, most of which did not employ MR analysis, no other ocular disorders displayed a significant causal link with vitamin D levels, either in the standard MR or multivariable analyses.

The study authors suggest that sunlight might serve as the crucial link explaining the causal relationship between vitamin D levels and wet AMD; sun exposure, which enhances vitamin D levels, is also a known risk factor for AMD.

“It has been shown that ultraviolet and blue light can lead to the damage of RPE cells,” the authors wrote in their paper. “A case-control study found that sunlight exposure during working life could increase the risk of early and late AMD, [and] individuals born in summer were observed to have a higher season-specific risk of neovascular AMD compared to those born in winter.” Vitamin D levels are also reportedly highest in August and lowest in February in the US. “Since sunlight exposure is the main source of vitamin D,” they continued, “we infer that additional sunlight exposure may increase the risk of wet AMD.”

In the end, the researchers convey that while higher genetically predicted vitamin D levels appear to elevate the risk of wet AMD, further research—especially involving a more ethnically diverse population—is warranted.