Body Mass Index Influences Age-Related Cataracts: An Updated Meta-Analysis and Systematic Review

Author: Chen H, Sun X, Pei L, Wang T.

Geographical coverage: Not reported

Sector: Body mass index

Sub-sector: Risk of age-related cataracts

Equity focus: Not reported

Study population: Patients with cataract

Review type: Effectiveness review

Quantitative synthesis method: Meta-analysis

Qualitative synthesis method: Not applicable

Background: Age-related cataracts (ARC), characterised by lens opacity and visual impairment, are a major cause of blindness throughout the world. The World Health Organisation classifies body mass index (BMI) as normal (18.5–25), overweight (25–30), and obese (>30), and recent studies have explored its potential link to ARC development. While some studies report no association, others suggest both high and low BMI levels could increase cataract risk. A higher BMI reduces the risk in some cases, especially for nuclear and cortical cataracts. Contrarily, obesity is significantly associated with cortical and posterior subcapsular cataracts. Variability in study findings could be due to demographic, genetic, or methodological differences. Therefore, these mixed results have fuelled ongoing debate over BMI’s role in cataract formation.

Objective: To quantitatively summarise the results regarding the effect of BMI on different ARC risk types.

Main findings: The review included 9 studies, with a sample size ranging from 362 to 3580.  According to the quality evaluation of the included studies, six were of moderate quality and three were of high quality.

The findings revealed that underweight patients were at an increased risk of ARC (odds ratio, OR=1.02, 95% confidence interval [CI]: 0.53 to 1.52, p<0.0001; I²=81.2%, p<0.0001). However, there was no difference between underweight and normal weight participants for nuclear cataracts (Nc, p=0.156), cortical cataracts (Cc, p=0.085).

However, overweight patients were at reduced risk of ARC (OR=0.94, 95% CI: 0.85 to 1.03, p<0.0001; I²=62.3%, p<0.0001). Furthermore, significant correlations were noted between overweight and Cc (OR=0.95, 95% CI: 0.66 to 1.24, p<0.0001), Nc (OR=0.92, 95% CI: 0.76 to 1.08, p<0.0001), and PSC (OR=0.87, 95% CI: 0.38 to 1.02], p<0.0001), respectively.

Meta-analysis also showed a significant association between obesity and ARC. Obesity increased the risk of cataracts (OR=1.05, 95% CI: 0.98 to 1.13, p<0.0001; I²=0.0%, p=0.592). Additionally, significant correlations were found between obesity and Cc (OR=1.00, 95% CI: 0.82 to 1.17, p<0.0001), Nc (OR=1.07, 95% CI: 0.92 to 1.22, p<0.0001), and PSC (OR=1.14, 95% CI: 0.91 to 1.37, p<0.0001), respectively.

Methodology:  The searches were conducted in Medline, PubMed, and Web of Science to identify observational studies reporting the correlation between BMI and ARC. The studies published in English between January 2011 to July 2020 were included in this review. The reference lists of the relevant meta-analyses were also scanned to identify additional relevant publications.

Two reviewers independently screened the articles and extracted the relevant data. Disagreements between the reviewers were resolved through discussion or by contacting a third reviewer. The quality of the included studies was assessed using the Agency for Healthcare Research and Quality (AHRQ). The findings were synthesised using a fixed or random-effects model meta-analysis based on the heterogeneity, which was assessed using the Cochrane Q-test and I² statistics. Publication bias was assessed using a funnel plot and Egger’s test.

Applicability/external validity: The review highlighted that the potential co-existence of obesity with other health conditions, such as diabetes and cardiovascular disease, may confound the observed associations between BMI and cataracts. Additionally, variation in cataract grading systems across studies introduces inconsistency in outcome measurement. Furthermore, the review noted a high risk of bias due to a lack of blinding and reliance on subjective assessment. It emphasised that the findings should be interpreted cautiously, and randomised trials are necessary to strengthen causal inference and broader applicability.

Geographic focus: The review did not apply any geographical limits. However, it did not report the geographical distribution of the included studies.

Summary of quality assessment: Overall, there is medium confidence in the review’s conclusions. The searches were conducted in Medline, PubMed, and Web of Science. Inclusion and exclusion criteria were clearly defined, and two reviewers independently screened the articles and extracted data, with disagreements resolved through discussion or consultation with a third reviewer. The study quality was assessed using established tools. Characteristics of included studies were well-documented, meta-analyses were appropriately performed, and heterogeneity was addressed. However, the search was limited to identifying articles published in the English language only, the review did not provide a list of excluded studies, and the findings were not reported by the risk of bias status.