Accumulated lead exposure may be an important risk factor for cataracts

12/01/04

Accumulated exposure to lead may be an important but unrecognized risk for developing cataracts in men, according to a study in the December 8 issue of JAMA.

Lead continues to pose a significant public health problem in spite of substantial reductions in lead exposure in the United States in the recent past, according to background information in the article. Exposure has not been totally eliminated and most adults continue to have substantial levels of lead in their body. Previous evidence has indicated that low-level lead exposure may increase the risk for a number of chronic age-related diseases.

Debra A. Schaumberg, Sc.D., M.P.H., of Brigham and Women's Hospital, Boston, and colleagues investigated whether bone lead levels measured in both the tibia and patella were associated with age-related cataract, the leading cause of blindness and visual impairment worldwide. Bone lead levels were measured 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, researchers reviewed eye examination data (collected routinely every 3 - 5 years) for the period after the bone lead measurements were taken. The study included men aged 60 years and older who had sufficient eye examination information available (n = 642). Blood lead levels were also measured.

The average age of the study participants was 69 years and cataract was identified in 122 men. The researchers found that men in the highest quintile of tibia lead level had a 2.7 times increased likelihood for cataract compared to men in the lowest quintile. Further adjustment for cigarette smoking, diabetes, blood lead levels, and intake of vitamin C, vitamin E, and carotenoids indicated a 3.2 times increased likelihood of having cataract among men in the highest quintile of tibia lead. For patella lead level, there was a 1.9 times increased likelihood of cataract in the highest vs. lowest quintile, but the trend was not significant. Blood lead levels, more indicative of short-term exposure levels, were not significantly associated with cataract.

"… generalized low lead exposure along with pockets of higher exposure remain commonplace, including in the United States where more than 80 percent of homes built before 1980 are contaminated by lead-based paint and/or leaded water pipes. Results of the present study suggest that cumulative lead exposure is a risk factor for cataract, which accounts for more than 40 percent of all cases of blindness worldwide," the authors write. They add that expenditures for cataract surgery comprise the largest single line item in the Medicare budget.

"These are, to our knowledge, the first data suggesting 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," the authors conclude.

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