Long-term exposure to lead linked to cataracts

A new study suggests that accumulated exposure to lead over a lifetime may contribute to increased risk for developing cataracts in older men.

The study, reported today in The Journal of the American Medical Association, showed that elderly men with the highest levels of lead in their shinbones had a 3.2 times greater risk of developing cataracts than those with the lowest lead levels in the bone.

"These 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," said Debra Schaumberg, a specialist in preventive health at Brigham and Women's Hospital in Boston and lead author of the study.

A cataract is a clouding of the lens in the eye that reduces the amount of light reaching the retina and is common in older people. About half of all people living into their 80s develop at least one cataract. The researchers note that the condition is responsible for 40 percent of all cases of blindness worldwide. In the United States, spending for cataract surgery is the largest single line item in the Medicare budget.

Other recent studies have shown that low levels of lead exposure may increase the risk for a number of chronic age-related diseases, including high blood pressure and mental decline.

Much of the lead that's taken into the body is incorporated into the bones where it regularly interchanges with other tissues through the marrow.

Several earlier studies have documented the presence of lead in eye lenses with cataracts. Scientists believe the intrusion of lead into the lens may contribute to the protein "clumping" across the surface that decreases the transparency of the lens.

Although there have been substantial reductions in lead exposure in this country with the elimination of the metal from many paints and from gasoline, lead continues to be a substantial public health problem. Most adults continue to have substantial levels of lead in their body, and there are pockets of higher exposure.

"More than 80 percent of homes built before 1980 are contaminated by lead-based paint and/or leaded water pipes," the researchers noted.

Older people may be more likely to have lived in those homes for much of their lives, even if they live in more modern structures now. The study group was drawn from a group of Boston-area men aged 60 and older (average 69) who are taking part in a long-term study of aging.

Of 642 men who had bone lead levels periodically measured, the researchers reviewed information on eye exams that were done every three to five years, and identified 122 with cataracts. Blood lead levels were also measured in the men, but this indicator of recent lead exposure was not significantly associated with cataracts.

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On the Net: www.jama.com; www.nei.nih.gov