Accumulated lead exposure and risk of age-related cataract in men

Low-level lead exposure may increase the risk for a number of chronic age-related diseases. Several studies have documented the presence of lead in lenses with cataract. The intrusion of lead into the lens may alter lens redox status and cause protein conformational changes that decrease lens transparency.

To determine the relationship of cumulative lead exposure with the development of cataract.

Tibial (cortical) and patellar (trabecular) bone lead levels were measured by K x-ray fluorescence between 1991 and 1999 in a subset of participants in the Normative Aging Study (NAS), a Boston-based longitudinal study of aging in men. Among the first 795 NAS participants to have bone lead levels measured, we reviewed eye examination data (collected routinely every 3-5 years) for the period after the bone lead measurements were taken. We limited the population to men aged 60 years and older who had sufficient eye examination information available (n = 642). Blood lead levels were also measured.

Cataract assessment was done while masked to the lead level results. A participant was considered to have cataract if there was documentation for either eye of cataract surgery or a cataract graded clinically as 3+ or higher on a 4-point scale. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated as estimates of the magnitude and significance of the relationship of lead exposure with cataract, in logistic regression models.

The mean age of the study participants was 69 years and cataract was identified in 122 men. The age-adjusted OR (95% CI) for cataract for men in the highest vs lowest quintile of tibia lead level was 2.68 (1.31-5.50). Further adjustment for pack-years of cigarette smoking, diabetes, blood lead levels, and intake of vitamin C, vitamin E, and carotenoids resulted in an OR of 3.19 (95% CI, 1.48-6.90). For patella lead level, there was an increased risk of cataract in the highest vs lowest quintile (OR, 1.88; 95% CI, 0.88-4.02), but the trend was not significant (P = .16). Blood lead levels, more indicative of short-term exposure levels, were not significantly associated with cataract (OR, 0.89; 95% CI, 0.46-1.72; P = .73).

These epidemiological data suggest that accumulated lead exposure, such as that commonly experienced by adults in the United States, may be an important unrecognized risk factor for cataract. This research suggests that reduction of lead exposure could help decrease the global burden of cataract.