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Lots of lead in the bones may make for an unhealthy heart, new research suggests.
Older men with the highest levels of the metal in their bones were more than twice as likely to die over the study's nine-year follow-up than their peers with the lowest bone lead levels, while their risk of dying from heart-related causes was nearly six times greater, Dr Marc Weisskopf of the Harvard School of Public Health in Boston and his colleagues found.
"This is yet another prod to try and raise the issue of bone lead being at least as important to monitor as blood lead," Weisskopf told Reuters Health. He pointed out that occupational standards for lead exposure are currently based on measuring blood levels, which can return to normal a few months after exposure ends. Bone lead, on the other hand, can show exposure that happened years or even decades ago.
"What our work is suggesting is that [blood lead] may not tell the whole story," he added. "Just because someone's blood lead level has dropped down doesn't mean they are necessarily safe or free from these concerns."
While suggestions that lead might be bad for the heart date back at least to Hippocrates, Weisskopf and his team note in the journal Circulation, the relationship between exposure to the toxic metal and heart health is still poorly understood. However, they add, high levels of blood lead have been tied to increased risk of death from many causes.
Increased risk for ischaemic heart disease
In the current study, the researchers looked at 868 men participating in a long-term study of ageing. Their average age was about 67. Weisskopf and his colleagues tested levels of lead in the men's kneecaps and in their shin bones.
During follow-up, 241 of the men died. Those who ranked in the top third based on their bone lead levels were 2.52 times more likely to die, and 5.63 times more likely to die from heart-related causes, than men with the lowest levels.
Once the researchers adjusted for age, smoking, and race, they found that the men with the highest bone lead levels were more than eight times as likely as those with the least lead in their bones to die of ischaemic heart disease caused by blocked arteries.
While it's not clear how lead might hurt the heart, Weisskopf noted that there are many plausible mechanisms; it could damage the "autonomic" nervous system, which controls the heart; boost blood pressure; or harm heart tissue.
Measuring bone lead could one day prove useful for identifying people at increased risk of heart disease, Weisskopf noted, but at present testing is cumbersome and expensive – and it's very difficult to take bone samples.
(Reuters Health, September 2009)
