Blood Lead Levels: What Is Safe?

September 18, 2006

NEW ORLEANS -- Levels of lead in the blood now considered safe increase the risk of death, epidemiologists reported today.

NEW ORLEANS, Sept. 18 -- Levels of lead in the blood currently considered safe increase the risk of death, epidemiologists reported today.

In a study of almost 14,000 adult Americans with serum lead concentrations of at least 0.17?mol/L, which was less than half of the current threshold considered safe, there was a 25% higher risk for all-cause mortality and 55% higher risk for cardiovascular mortality than those with lead concentrations below 0.09 ?mol/L.

Those in the highest tertile of serum lead concentration (?0.17?mol/L) had a hazard ratio of 1.25 (95% confidence intervals 1.04-1.51 P trend across tertiles =0.002) for all cause mortality and 1.55 (95% CI 1.08-2.24 P trend across tertiles=0.003) for cardiovascular mortality, compared with those in the lowest tertile of serum lead concentration, reported Paul Muntner, Ph.D., of Tulane, and colleagues at Johns Hopkins, in Circulation, Journal of the American Heart Association.

Previous studies have linked lead levels of more than 0.48 ?mol/L with increased risk of death, but the authors said there has been little research into risks of lower blood lead levels, although 99% of U.S. adults have blood lead levels below 0.48 ?mol/L.

The increased mortality was in non-Hispanic whites, non-Hispanic blacks, and Mexican Americans both males and females, the authors wrote.

Moreover, a blood lead level greater than 0.10 ?mol/L was also significantly associated with both myocardial infarction and stroke mortality.

Dr. Muntner and colleagues studied blood samples collected from 13,946 participants in the Third National Health and Nutrition Examination Survey (NHANES). The participants were recruited from 1988 to 1994 and then followed for 12 years. Mortality data were collected from the National Death Index.

The geometric mean blood lead level in the study sample was 12 ?mol/L, the authors wrote.

The authors pointed out a number of limitations of the study including its reliance on a single blood lead measurements because blood lead has a half life of about 30 days, so concentrations could reflect either recent or ongoing exposure.

Bone lead measurements, they wrote, would be a better measure of cumulative lead exposure.

Moreover, there was a significant decrease in lead exposure in the U.S. population over the course of the study and "because of regression dilution bias, the decrease in blood lead observed at the population level implies that the result of the present study are conservative and that the lead-mortality relationship may be stronger than reported."

Nonetheless, the authors wrote that the latest available NHANES data suggest that 30% of U.S. adults have lead levels that are higher than 0.10 ?mol/L, which lead them to conclude that the public health implications of their findings are substantial.

The results of the study, they wrote, require that lead exposure of less than 0.48 ?mol/L should be included among adult-related cardiovascular risk factors.

There was no association between lead blood levels below 0.48 ?mol/L and cancer mortality.