A significant cause of cataracts may be due to lifelong accumulation of lead, a link that adds to a growing list of medical conditions associated with the toxic metal, researchers report in an analysis published Wednesday.

Lead has an affinity for the bones and can remain as part of the microscopic latticework of the skeleton for decades, say experts who have studied a new — and worldwide — health effect linked to the heavy metal. Lead’s toxicity has been known for centuries, but “the 20th century left a legacy of unprecedented lead levels spread throughout the environment,” scientists report in Wednesday’s Journal of the American Medical Association.



Dr. Debra Schaumberg, an assistant professor of medicine at Harvard Medical School, said the study is the first to find an association between the metal and cataracts. Previous studies linked lead exposure to other conditions of age, such as high blood pressure and dementia.



The poisonous element remains a significant public health threat, she said, despite substantial efforts to reduce its use. In children, lead has been linked to learning disabilities and mental retardation.



Schaumberg, who led the new research, examined the amount of lead in nearly 800 men 60 and older in Boston and found that those with the highest levels in their tibias — shin bones — were 2.7 times more likely to have cataracts. She estimates that 42 percent of them had cataracts directly linked to lead. Schaumberg believes the finding also applies to women.



“There are two things about lead,” Schaumberg said Tuesday. “Once it gets into the body, it stays for a very long time. Also, people get exposed in a number of ways — through drinking water, through workplace exposures and in their homes through lead paint.” Lead-tained dust is common in cities and on roadways worldwide, the result of leaded gasoline. The fuel was outlawed in the United States 25 years ago, but Schaumberg said in places such as Mexico City, where leaded fuel is still used, accumulations may be substantially higher than in this country.



Cataracts, which develop gradually and painlessly, are a clouding and yellowing of the eyes’ lens. The condition affects 20.5 million people 65 or older in the United States and is a leading cause of blindness.



Dr. Nathan Graber, a fellow in environmental health at Mount Sinai School of Medicine in Manhattan, said lead exposure is inescapable. Stored in the bones, lead stays put unless prompted out.



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