Lead Linked To Premature Deaths In Adults
Mortality Rate 46% Higher In Those Exposed To Metal Earlier In Life, Study SaysDec 28, 2002 | The Baltimore Sun Lead is the No. 1 environmental health hazard for children, but a new study indicates that more than 30 million American adults may be at risk of premature death because of past exposure to the metal.
The study, reported in late November in the Archives of Internal Medicine, found that people who had elevated blood levels of lead earlier in life have a 46 percent increased rate of mortality from all causes later on, indicating that children may carry a legacy of lead toxicity as they age.
Children are especially vulnerable to the effects of lead, and it has long been known that lead can cause mental retardation in those exposed to relatively modest levels. But once children reached adulthood it was thought they would be more resistant to the damage.
Experts say the findings underscore the importance of enforcing laws regulating the removal of lead paint from older houses, where children can ingest lead in dust and paint chips.
"Clearly, this argues for much more aggressive abatement and enforcement of these laws, as we've been doing," said Dr. Peter L. Beilenson, health commissioner in Baltimore, where recent efforts have resulted in significant drops in the number of children with lead poisoning. "There's even better reason now to reduce your kid's risk of living in this. Not only does it cause behavioral and other problems, but it also apparently causes an increase in mortality."
Researchers said the new study also suggests that federal standards for the amount of lead adult workers can have in their blood may be set dangerously high.
"This is a very important new study," said Dr. Peter Orris, director of the Occupational Health Services Institute at the University of Illinois at Chicago. "It indicates that there is increased cardiovascular and cancer mortality in adults at blood lead levels we haven't been concerned about before."
The research also sheds light on the reason African-Americans who tend to be exposed to more lead in the environment have significantly increased rates of some diseases, especially high blood pressure, which has been linked to elevated lead levels.
Lead's danger to children led to the gradual elimination of leaded gasoline and lead paint, the two major sources of lead in the environment. Lead was banned from residential paint in 1978, and leaded gasoline was phased out by 1986. Blood lead levels have since plummeted greatly.
A serious threat
But for people in their late 30s and older who were exposed to much higher levels of lead before the bans, the heavy metal poses a serious threat to their lives, said Ellen Silbergeld of the Johns Hopkins University, who worked on the study with Mark Lustberg of the University of Maryland School of Medicine.
"This is a study of people who had prior elevated lead exposures, as most of us did people who were born before 1975 and grew up under conditions where we had blood lead levels that were substantially within the range that we're associating with these later risks," she said.
Her findings show that people who had elevated blood lead levels although still below those considered safe in industry had a significantly higher rate of death, especially from heart disease, than people who had much lower blood levels.
"Lead's effects are leveraged through many different organ systems," said Dr. Howard Hu, professor of occupational and environmental medicine at the Harvard School of Public Health.
"When you put it all together, lead is probably having a very real public health impact," said Hu, whose studies showed that lead exposure can cause high blood pressure, a major risk factor for heart disease. "It's not just organ dysfunction. It's not just subclinical kidney function. It's a real effect on mortality."
Unlike iron, zinc, chromium and selenium, lead serves no known useful purpose in the body. It stubbornly settles in bone, brain and other tissue - remaining there for many decades - to block nerve cell communication, disrupt heart rhythm, reduce artery elasticity and interfere with genetic functions.
High levels of lead have been found in the bones of ancient Romans, who used lead widely, including to line drinking-water pipes and to sweeten wine. Because long-term lead exposure can affect not only the heart but also the central nervous system, reproductive system, kidneys and blood-forming function, some experts say the accumulated effects could have weakened the Roman population over time, contributing to the decline of the empire.
Recent research shows that chronic elevated lead levels, such as from a workplace environment, can lead to mental deterioration later in adulthood as well as reduced nerve control of muscles.
Silbergeld's study involved more than 20,000 people nationwide, dating to 1976, and accounted for other risk factors such as age, sex, smoking, weight, education, neighborhood, exercise and income.
She found that people who had blood lead levels of from 20 micrograms to 29 micrograms per deciliter in the '70s had nearly a 50 percent increased death rate over those whose lead levels were below 10 micrograms.
"We would estimate between 16 [percent] and 19 percent of deaths due to cardiovascular disease can be attributed to lead exposure," Silbergeld said.
In the late 1970s, the average lead level in the U.S. population was 14 micrograms, and about 15 percent of the population - or 29 million people - had levels in the range of from 20 micrograms to 29 micrograms or above, Silbergeld said.
These are the people who still bear the toxic lead burden and should be tested for early signs of high blood pressure and other problems, she said. Effective treatments are available for many of these conditions, she added.
About 1.7 million people, primarily workers exposed to lead on the job, have readings of from 20 micrograms to 29 micrograms.
The federal Occupational Safety and Health Administration permits blood lead levels in workers of 30 micrograms per deciliter. OSHA limits a worker's exposure to the job site when levels reach 40 micrograms and requires removal from the job at 50.
"Since we're seeing elevations in deaths at the current OSHA standards, that suggests that our current occupational health standards for lead are not protective," Silbergeld said.
Hu agreed: "The conclusion is clear. The current occupational lead standards are out of date and should be lowered."
Recently, the U.S. Department of Health and Human Services recommended that occupational lead exposure be limited to less than 25 micrograms.
Blood lead levels for the average person in the United States are about 3 micrograms per deciliter, but they are much higher in certain pockets, such as older urban housing where children and adults are exposed to lead-based paint.
Throughout the 1990s in Baltimore, for instance, about 7,000 children a year were being exposed to lead, but only a fraction were being tested for exposure. In the past few years, stepped-up efforts to test children, repair hazardous housing and prosecute landlords for lead paint violations has resulted in a 24 percent drop in the number of city children with elevated lead levels.
"This bodes well for the city down the road," Beilenson said, pointing out that the efforts will probably translate into less violence, fewer kids on special education, and, if the new study is right, fewer people dying.
Eighty percent of houses built before 1978 contain lead paint. Although local, state and federal agencies have programs to remove lead from homes, those in the poorest neighborhoods still have the highest levels.
The Centers for Disease Control and Prevention estimate that 30 percent of children in inner cities have high lead levels. The CDC estimates that 1 million children have lead levels of 10 micrograms or higher, which increases their risk of developing learning disabilities and behavior problems.
Part of the reason that African-Americans have higher rates of high blood pressure and heart disease may be that they are exposed to higher levels of lead beginning in infancy, Silbergeld said.
Ronald Kotulak writes for the Chicago Tribune, a Tribune Publishing newspaper. Sun staff writer Diana K. Sugg contributed to this article.