Abstract
Abstract: :
Purpose: The hazards of lead exposure in young children are well known, but effects of chronic, lower level lead exposure in adults have been less well studied. Several studies have shown higher levels of lead in cataractous lenses as compared to clear lenses, and the intrusion of lead into the lens may alter lens redox status and cause protein conformational changes that affect lens transparency. The purpose of this study was to determine the relationship of cumulative low-level lead exposure with the development of cataract. Methods: We measured bone lead levels rather than blood lead levels since blood levels are known to be poor indicators of chronic exposure. Tibial (cortical) and patellar (trabecular) bone lead levels were measured by K x-ray fluorescence (K-XRF) beginning in 1991 in a subset of participants in the Normative Aging Study (NAS), a longitudinal study of aging in men that began in 1961. Among the first NAS participants to have bone lead measurements taken, we selected for this study those men with levels in the upper (N=79) or lower (N=79) quintiles for tibial lead, matching for age within 2 years. We assessed cataract by review of NAS subjects' eye examination data (collected routinely every 3 to 5 years) for the period following the bone lead measurements. Cataract assessment was done masked to lead status. A subject 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. We used conditional logistic regression to estimate the magnitude and significance of the relationship of lead exposure with cataract. Results: The average age of the study subjects was 66.8 years. Cigarette smoking was significantly more common among men with high (83.5% ever smoked) versus low levels of bone lead (53.2% ever smoked) (P=0.001). Of the men in the high bone lead group, 22% developed cataract, while 9% developed cataract in the low bone lead group. After adjustment for pack-years of cigarette smoking, the odds ratio (95% confidence interval) for high versus low lead levels remained elevated at 3.01 (1.12 to 8.09). Additional adjustment for diabetes did not affect this finding. Conclusion: These are the first data suggesting that chronic low-level lead exposure, such as that commonly experienced by adults in the US, may be an important unrecognized risk factor for cataract. If confirmed in larger studies, this research suggests that reduction of lead exposure could help decrease the global burden of cataract.
Keywords: 338 cataract • 355 clinical (human) or epidemiologic studies: risk factor assessment