In a new study, the risk of death from cardiovascular disease was almost six times higher in men with the highest concentrations of bone lead compared to men with the lowest concentrations. The risk of death from all causes was 2.5 times higher in men with the highest levels of lead compared to those with the lowest levels.
"Cumulative exposure to lead, even in an era when current exposures are low, represents an important predictor of cardiovascular death," said Marc Weisskopf, Ph.D., Sc.D., lead author of the study and assistant professor of environmental health and epidemiology at the Harvard School of Public Health in Boston.
"The findings with bone lead are dramatic. It is the first time we have had a biomarker of cumulative exposure to lead and the strong findings suggest that it is a more critical biomarker than blood lead."
Researchers analyzed 868 primarily Caucasian men living in the greater Boston area who are participating in the U.S. Department of Veterans Affairs' Normative Aging Study. At the start of the study, when men received their first bone lead measurement, the average age was 67 years. They were followed for about nine years; 241 died during the study.
Traditionally, lead exposure has been measured in blood in surveillance studies and in the clinic. Blood lead is the only lead biomarker used by the Occupational Safety and Health Administration (OSHA) and the National Health and Nutrition Examination Surveys (NHANES).
Blood has a short half-life of about 30 days. Bone has a half-life ranging from years to decades and represents cumulative exposure to lead.
Researchers routinely measured blood lead and two different kinds of bone lead in the patella (kneecap) and tibia (shin). They used a technique similar to a chest X-ray to assess lead concentrations in bone. The half-life of the kneecap is about eight years, while the shin may have a half-life of decades.
The study's results have important public health implications, Weisskopf said. "Researchers studying cardiovascular deaths worldwide have generally not considered lead as one of the risk factors that contributes to the risk of death from cardiovascular disease."
He called for more emphasis on measuring bone lead in surveillance and regulatory activities.
Although few if any participants in the study were occupationally exposed to lead, there are certain occupations at high risk for lead exposure: e.g. construction workers and painters. These results suggest that the current OSHA standards--based solely on blood lead levels and permitting levels up to 40 micrograms of lead per deciliter—are likely inadequate and don't capture the full impact of cumulative exposure to lead, Weisskopf said.
"In addition to spurring additional public health measures to reduce exposure to lead, mechanistic and clinical research is needed to determine if opportunities exist to conduct targeted screening and treatment that can further reduce the burden of cardiovascular disease for the potentially millions of adults who have elevated lead burdens accumulated from historical exposures," said Howard Hu, M.D., co-author, NSF International Chair of the Department of Environmental Health Sciences and professor of Environmental Health, Epidemiology and Internal Medicine at the University of Michigan Schools of Public Health and Medicine.
A major source of U.S. environmental lead exposure in the past was through inhalation of airborne lead largely from the use of leaded gasoline, Weisskopf said. The U.S. banned lead in gasoline in the mid 1990's. Airborne lead is still found today in the U.S., but at much lower levels than when leaded gasoline was used. In general, other potential sources of exposure are lead in paint (although the sale of residential lead-based paint is banned, flaking or chipping paint from older houses can lead to exposures), lead in water in places where lead in the pipes is still present. Lead can also find its way into food and so ingestion of lead (through food or water) is now one of the more common sources of exposure to the general U.S. population (along with inhalation of airborne lead).
Some hobbies can also be associated with exposure: use of or casting ammunition, toy soldiers, fishing weights, lead in solder for making stained glass or some ceramic glazes, he said.
All study co-authors are: Marc Weisskopf, Ph.D., Sc.D.; Howard Hu, M.D.; Nitin Jain, M.D.; Huiling Nie, Ph.D.; Joel Schwartz, Ph.D.; David Sparrow, D.Sc.; and Pantel Vokonas, M.D.
For more information visit the American Heart Association.