New Study Links Lead Exposure with Increased Risk of Cataract
Results from a new study show that lifetime lead exposure may increase
the risk of developing cataracts. Researchers found that men with
high levels of lead in the tibia, the larger of the two leg bones
below the knee, had a 2.5-fold increased risk for cataract, the
leading cause of blindness and visual impairment.
"These results suggest that reducing exposure of the public
to lead and lead compounds could lead to a significant decrease
in the overall incidence of cataract," said Kenneth Olden,
Ph.D., director of the National Institute of Environmental Health
The National Institute of Environmental Health Sciences, one of
the National Institutes of Health, provided support to researchers
at the Harvard School of Public Health and Brigham and Women's Hospital
for the nine-year study, which is also focusing on lead's contribution
to hypertension and impairment of kidney and cognitive function.
The findings on risk of cataract are published in the December 8th
issue of the Journal of the American Medical Association.
Lead is found in lead-based paint, contaminated soil, household
dust, drinking water, lead crystal, and lead-glazed pottery. Following
exposure to lead, the compound circulates in the bloodstream and
eventually concentrates in the bone.
The Harvard researchers tested whether bone lead levels measured
in both the tibia and patella, also known as the kneecap, were associated
with cataract in an ongoing study of men taken from the Boston area.
"Given the strong association between tibia lead and cataract
in men, we estimate that lead exposure plays a significant role
in approximately 42 percent of all cataracts in this population,"
said Debra Schaumberg, Sc.D., assistant professor of medicine and
ophthalmology at Harvard Medical School and lead author of the study.
"While lead in both the tibia and patella was associated with
an increased risk of cataract, tibia lead was the best predictor
of cataract in the study sample."
According to Schaumberg, cataracts develop as a result of cumulative
injury to the crystalline lens of the eye. "Lead can enter
the lens, resulting in gradual injury to certain proteins present
in the epithelial cells, and this eventually results in a cataract,"
The Harvard researchers are among the first to use bone lead in
studying the effect of lifetime lead exposure on disease risk. "The
best biological marker for estimating a person's cumulative exposure
to lead is provided by skeletal lead," said Dr. Howard Hu,
professor of occupational and environmental medicine at the Harvard
School of Public Health and co-author of the study. "Since
blood lead levels reflect only recent exposures, they are not likely
to predict the development of age-related diseases such as cataract,
which take many years to develop."
Cataracts, a clouding of the lens resulting in a partial loss of
vision, are very common in older people. By age 80, more than half
of all Americans either have a cataract or have had cataract surgery.
Other risk factors for cataract include diabetes, smoking, long-term
alcohol consumption, and prolonged exposure to ultraviolet sunlight.
The prevention of age-related cataract remains an important public
health goal," said Schaumberg. "In addition to the obvious
problems of reduced vision, the visual disability associated with
cataracts can have a significant impact on the risk of falls, fractures,
quality of life, and possibly even mortality.