Lead might have been banned from petrol in many parts of the globe, but millions of people will grow old faster than they should because of past exposures to the toxic metal, according to a new study.
Two studies conducted at Johns Hopkins University in Maryland and the University of Michigan have revealed that lead accelerates ageing by up to six years, and can remain in the body for years after the exposure.
The harmful effects of exposures to the metal include memory loss and difficulties with language.
The researcher say that lead has the ability to accumulate and lie hidden in the bones of the human body, and thus they were able to measure middle-aged to elderly people's past exposure, and relate it to their process of mental decline.
During a study, the Johns Hopkins researchers looked at 1,000 people aged 50 to 70, estimated past doses by scanning their shinbones, and gave them tests for their mental ability.
They found that the higher the dose the more they suffered from "accelerated ageing", with a deteriorating ability to think, learn, remember and express themselves.
They also found that the subjects who had the most lead aged up to six years faster than those with the least.
"A portion of what has been called normal ageing might in fact be due to ubiquitous environmental exposures like lead," the Independent quoted Professor Brian Schwartz, who led the research, as saying.
In the other study, the University of Michigan researchers tested elderly men twice, some years apart.
The study, however, produced strikingly similar results, concluding that the metal hastened ageing by five years.
Professor Ellen Silbergeld of the Johns Hopkins Bloomberg School of Public Health says that lead that has been lurking in the skeleton gets released into the blood when bones lose calcium through ageing, spreading its poison throughout the body.
A study from Boston University recently showed that lead was contained in a fifth of the ayurvedic medicines being sold on the Internet.
Other researchers have found that children having lead in their blood are four times more likely to develop attention deficit hyperactivity disorder (ADHD), and established a "very strong association" between the exposure of young children to the toxic metal and crime rates some 20 years later, when they have become young adults.
Scientists are now worried that other pollutants that accumulate in the body - such as mercury and many pesticides - may similarly be biding their time to wreak havoc.