Association between vitamin D level and cataract: A systematic review and meta-analysis

Author: Jue Z, Xu Z, Yuen VL, Chan ODS, Yam JC.

Geographical coverage: Egypt, Iran, Korea and Turkey

Sector: Cataracts

Sub-sector: Vitamin D

Equity focus: Not reported

Study population: Patients with cataract

Review type: Effectiveness review

Quantitative synthesis method: Meta-analysis

Qualitative synthesis method: Not applicable

Background

Cataract remains a leading cause of blindness globally, accounting for roughly one-third of all cases and affecting more than 50 million people with moderate-to-severe vision loss. Both genetic and environmental factors contribute to cataract development. Vitamin D regulates gene expression and exerts anti-inflammatory and anti-apoptotic effects, and deficiency has been linked to several ocular diseases. Whether low vitamin D status is associated with cataract, however, is uncertain.

Objective

To determine the association between serum vitamin D concentration and the presence of cataract.

Main findings

Four observational studies (three case–control, one cross-sectional) involving 10 928 cataract cases and 10,117 controls from Egypt, Iran, Korea and Turkey were included. Study quality was moderate (Newcastle–Ottawa scores 6–7).

• Overall association
  • Cataract patients had lower vitamin D levels than controls (mean difference [MD] –4.87 ng/mL, 95 % CI –9.67 to –0.07; P = 0.047).
• Sex-specific analyses
  • Males: MD –2.15 ng/mL (95 % CI –3.83 to –0.46; P = 0.01).
  • Females: MD –6.67 ng/mL (95 % CI –8.20 to –5.14; P < 0.01).
    The association was stronger in females.
• Cataract subtype analyses
  • Nuclear: MD –10.48 ng/mL (95 % CI –12.72 to –8.24; P < 0.01).
  • Posterior subcapsular: MD –6.05 ng/mL (95 % CI –11.30 to –0.80; P = 0.02).
  • Cortical: not significant (MD –6.74 ng/mL; 95 % CI –15.70 to 2.22; P = 0.14).

Overall, lower circulating vitamin D appears associated with higher risk of cataract, particularly nuclear and posterior-subcapsular subtypes, and the effect may be greater in women.

Methodology

PubMed, Web of Science and EMBASE were searched to 30 August 2023 for English-language human studies comparing serum or plasma vitamin D levels in cataract versus control groups. Two reviewers independently screened records, extracted data and assessed quality (Newcastle–Ottawa Scale). Fixed- or random-effects models were chosen according to heterogeneity (I² threshold 50 %). Subgroup, sensitivity (leave-one-out) and publication-bias (Egger’s test) analyses were performed.

Applicability / external validity

Only four moderate-quality studies, using differing designs, populations and vitamin D assays, were available, and heterogeneity was high. Findings should therefore be interpreted cautiously. Larger prospective studies with standardised vitamin D measurement are required.

Geographic focus

No geographical limits were set; included studies were from Egypt, Iran, Korea and Turkey.

Summary of quality assessment

Overall confidence in the review’s conclusions is medium. Searches were comprehensive and dual-review processes followed; study characteristics were documented and appropriate meta-analyses conducted with heterogeneity explored. Limitations include English-language restriction, absence of an excluded-studies list and no reference-list or expert searches.