Lead may be a significant cause of high blood pressure, even more important than sodium or age, a Harvard study found.
Although they acknowledged more work needs to be done, researchers say their findings that people with higher lead levels were more likely to develop high blood pressure could shake up current thinking on hypertension. The study also could change how lead absorption in adults is gauged and force reductions in recommended lead exposure limits.The results may also help explain why blacks are more likely than whites to suffer from high blood pressure, said Howard Hu, who headed the study published in today's issue of The Journal of the American Medical Association. Many blacks live in depressed areas with flaking lead paint and lead water pipes.
"We undertook the study to clarify the relationship of lead levels in blood and bone to disease, since previous work in adults concerning lead exposure and blood pressure have been mixed," said Hu, an epidemiologist at Harvard Medical School.
Since blood levels reflect only recent exposure, the Harvard team checked levels of lead in the bone. Previous research has shown that adult bones retain 90 percent to 95 percent of the lead the body has absorbed.
"This provides elegant confirmation of the relationship between lead and hypertension," said Dr. Philip J. Landrigan, professor of community medicine at Mount Sinai Medical Center in New York. He said the Centers for Disease Control and Prevention showed links going back as far as 1985.
"It's documented in much more significant fashion here than before because they used the bone lead test," Landrigan said.
From 1991 to 1994, researchers scanned for lead in the left shinbone and kneecap of 590 Boston-area men who were participating in an earlier Veterans Administration study on aging. Those who had a history of hypertension and other chronic ailments when the larger VA study began in 1961 were eliminated.
Researchers determined that the three most significant factors in high blood pressure were body mass index, which is a ratio of height and weight, a family history of hypertension and shinbone lead level. Sodium intake and age ranked lower.
The group did not find a threshold above which lead levels caused high blood pressure. But when the group was broken evenly into five parts, the group with the highest lead levels was 50 percent more likely to develop hypertension than the group with the lowest, Hu said.
Hypertension attributed in the past to age may instead be a result of long-term lead accumulation, researchers said.
Eileen Silbergeld, a professor of epidemiology at the University of Maryland Medical School in Baltimore, raised doubts about the study's methodology. She said the study did not make clear whether lead has an independent effect on hypertension or combines with some other risk factors, such as age.
Much of the research on lead absorption has focused on children. Lead can damage their developing nervous systems and stunt their intelligence.