VITAMIN D DEFICIENCY AND THE RISK OF CATARACT: A MENDELIAN RANDOMISATION STUDY

Previous studies have suggested a preventative role in increased serum 25-hydroxyvitamin D levels on age-related cataracts. Other studies have suggested an increased risk of early age-related cataracts in younger patients with vitamin D deficiency (VDD). Unfortunately, many of these studies are limited due to the presence of confounding factors, making the distinction between correlation and causation difficult. Without evidence of causality, it is difficult to establish if an intervention targeting vitamin D levels (VDLs) will be able to prevent cataracts.

To test the causal evidence and estimate the causal effect of vitamin D on cataracts, we used a naturally occurring randomisation experiment, called Mendelian randomisation (MR), which relies on the random allocation of genetic variants in relation to other characteristics at conception. 

An epidemiological study of published data.

Information for the genetic predisposition of vitamin D levels and deficiency were obtained from the SUNLIGHT consortium of 79,366 individuals from 31 cohort studies and the UK Biobank of ~500,000 participants which includes 35,076 vitamin D deficient cases (VDLs <25 nmol/L), respectively.

Genetic information for cataracts was obtained from the FinnGen consortium, of 218,792 individuals.  Two subcategories of cataracts were tested: senile cataracts and cataracts others.

Four MR analyses were performed between the two vitamin D characteristics (levels and deficiency) and the two cataract categories (senile and others). Additional sensitivity analysis was conducted to test the robustness of the results.

We did not find evidence to suggest that vitamin D deficiency predisposition is associated with either senile cataract, or other forms ([OR= 0.965; 95% CI 0.916 to 1.016, p= 0.170], [OR= 0.993; 95% CI 0.929 to 1.062, p= 0.839], respectively). We were also unable to find evidence that predisposition for vitamin D level is associated with senile cataract or other forms of cataract ([OR= 1.153; 95% CI 0.905 to 1.470, p= 0.249], [OR= 0.947; 95% CI 0.653 to 1.375, p= 0.775], respectively). Our sensitivity analysis did not detect any violations of the MR assumptions that may have influenced our results. 

Our results do not support the presence of a modifiable effect of either vitamin D levels or deficiency on cataracts risk. Due to this, we cannot recommend vitamin D supplementation as a preventive measure against cataracts.