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High Lead Levels Linked to Cataracts

Those with greatest accumulated concentration had nearly triple the risk, study finds

TUESDAY, Dec. 7, 2004 (HealthDayNews) -- Long-term exposure to lead is linked to an increased risk of cataracts, a new study finds.

The study of almost 800 men in their late 60s found that those with the highest levels of lead in their bones were 2.7 times more likely to have cataracts than those with the lowest levels.

The report appears in the Dec. 8 issue of the Journal of the American Medical Association.

The fact that lead causes oxidative damage to body tissues in general prompted the researchers to study the relationship between the metal and cataracts, said Debra A. Schaumberg, the lead author of the report and an assistant professor of medicine and ophthalmology at Brigham and Women's Hospital in Boston.

A cataract is a cloudy or opaque area in the lens of the eye that can cause vision problems, even blindness, and Schaumberg said it "is one of the key diseases that we know are definitely related to oxidative stress and oxidative damage."

A key finding of the study is that the incidence of cataracts was linked to years-long exposure to lead in the environment, Schaumberg said.

The researchers determined this by measuring lead levels in the tibia and patella bones of the study participants over a period of 9 years and then collecting eye exam data for the same period of time. The participants all came from a subset of the ongoing Normative Aging Study, a Boston-based longitudinal study of aging in men.

"In the tibia [a bone in the lower leg], the life of the bone is 10 years or more," Schaumberg said. "In the patella [a bone in the knee], it is one to three years. We think the patella is a better marker of long-term exposure to lead."

And she added, "The cells in the lens are those you are born with. You keep those cells your whole life. There is no turnover."

The study found a strong relationship between cataract incidence and lead levels in the tibia and a much weaker link to lead levels in the patella, the researchers said.

Additionally, the study found no relationship between cataract risk and levels of lead in the blood, which can vary over the short term.

Dr. Ivan R. Schwab, professor of ophthalmology at the University of California, Davis, and a spokesman for the American Academy of Ophthalmology, praised the study as "first class." But he said more research is needed to prove the lead-and-cataract link.

"They have uncovered a potential risk factor, but the limitations of the study mean that its findings have to be confirmed by other studies," Schwab said.

It's possible that high lead levels are not directly responsible for damage to the eye but are a marker of other risk factors, he added.

For example, smoking is known to increase the risk of cataracts, and there is lead in cigarette smoke, Schwab said. Also, older, less-expensive homes are more likely to still have lead-based paint, so high lead levels in bones "could be a marker for socioeconomic status," he said.

"The poorer you are, the more likely you are to get lead in your system," Schwab said. "So high lead levels may be associated with other things that cause cataract."

Whatever the relationship, the study should add motivation to protect yourself against the toxic power of lead in the environment, Schaumberg added. Government has taken some important steps, such as eliminating lead in gasoline, but there are many things any individual can do, she said.

"Make sure you don't have high levels of lead in your drinking water," she said. "If you remodel your home, be sure you don't use lead-based paint."

On-the-job exposure to lead can also be dangerous, Schaumberg added. "Current regulations allow levels of up to 40 micrograms per deciliter of blood," she said. "That can result in a cumulative lead burden three to four times higher than what we found to be associated with cataract risk. It is better to reduce that exposure."

More information

For more on cataracts, visit the National Library of Medicine.

SOURCES: Debra A. Schaumberg, Sc.D, assistant professor of medicine, Brigham and Women's Hospital, Boston; Ivan R. Schwab, M.D., professor of ophthalmology, University of California, Davis; Dec. 8, 2004, Journal of the American Medical Association
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