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Lead in Blood: 'Safe' Levels Too High?

Sept. 18, 2006 -- The average blood level of lead found among Americans is high enough to increase the likelihood of heart attack and stroke, according to a new study.

In fact, people with only a fifth the level of lead in their blood now considered 'high' are more likely to die of heart attack or stroke, the study shows.

These findings suggest the threshold for 'high' blood levels of lead may not fully take into account lead's heart risks, according to the study.

The study appears in Circulation's rapid access online edition.

A 'high' blood level is now defined as more than 10 micrograms of lead per deciliter of blood (10 mcg/dL).

Most Americans -- 99% -- fall below that threshold, write the researchers, who include Andy Menke, MPH, of Tulane University School of Public Health.

But an increased likelihood of death from heart attack or stroke has started to be seen in people with blood levels greater than 2 mcg/dL, according to Menke and colleagues.

U.S. blood lead levels have dropped since the mid-1970s, with the phase-out of leaded gasoline and leaded paints, but they are still higher than before industrialization, Menke's team notes.

14,000 Adults Tested

Data for the study came from nearly 14,000 adults who had their blood lead levels checked between 1988 and 1994 for government health studies.

Their average blood lead level was 2.58 mcg/dL.

Those with higher blood lead levels were more likely to be older, black or Mexican American, male, and smokers.

They were also more apt to have low income, high blood pressurehigh blood pressure, high cholesterolhigh cholesterol, and no high school degree.

Participants were followed for up to 12 years, until the end of 2000.

During that time, a total of 1,661 participants died.

That number includes 267 from heart attacks, 141 from stroke, and 411 from cancercancer.

After adjusting for risk factors such as ethnicity, income, education level, and urban living, the researchers found that those with blood levels greater than 2 mcg/dL were more likely to die of heart diseaseheart disease, heart attack, or stroke -- but not cancer.

For their study, the researchers divided the adults into three groups based on blood lead levels. The highest had a blood level from 3.63 mcg/dL to 10 mcg/dL. The lowest had less than 1.93 mcg/dL.

Compared with the lowest blood level group, the highest had an 89% increased risk for death from heart attack.

The risk of death from stroke was 2.5 times greater in the highest blood level group than in the lowest.

Such increased risks started at blood levels greater than 2 mcg/dL.

It's not clear if the lead levels reflected current or past lead exposure, the researchers note.