14 DAY TRIAL // The toxicity of lead is notorious, but what we did not know was the impact it has on us, decades after being exposed to it. New researches point to the fact that a past lead exposure can age a person's brain by five years! If further research confirms this, then sharp cuts in environmental lead levels over 20 years ago still have an impact on us, signals Physorg.com. "We're trying to offer a caution that a portion of what has been called normal aging might in fact be due to ubiquitous environmental exposures like lead," Dr. Brian Schwartz of Johns Hopkins University, author of one of these researches, told Physorg.com.
"The fact that it's happening with lead is the first proof of principle that it's possible. Other pollutants like mercury and pesticides may do the same thing," said Schwartz.
Other recent researches have shown that pesticide exposure boosts the risk of Parkinson's disease a decade or more later. "It certainly makes sense that if a substance destroys brain cells in early life, the brain may cope by drawing on its reserve capacity until it loses still more cells with aging. Only then would symptoms like forgetfulness or tremors appear," Dr. Philip Landrigan of the Mount Sinai School of Medicine, in New York, told Physorg.com.
"Infant mice exposed to chemicals like PCBs show only very subtle effects in young adulthood. But more dramatic harm in areas like movement and learning appears when they reach old age," said Linda Birnbaum, director of experimental toxicology at the U.S. Environmental Protection Agency. Lead is easier to follow up in humans, as it accumulates in bones (like the shinbone) over decades, a mark of how much lead a person has been exposed along the time, while lead found in the blood shows recent exposure. We all have lead in the blood, but the levels have dropped in the last years. For example, the average lead amounts in the blood of the Americans decreased by 30% in the '80s, and by 80% in the '90s.
A 2006 research conducted by Schwartz's team was made on 1,000 Baltimore residents, aged 50 to 70, a generation that was exposed to a lot of lead coming from gasoline. "They probably got their peak doses in the 1960s and 1970s, mostly by inhaling air pollution from vehicle exhaust and from other sources in the environment," said Schwartz.
The team discovered that a higher lifetime lead dose was connected to weaker mental skills, like verbal and visual memory and language ability, similar to 2-6 years of brain aging. In 2004, a team led by Dr. Howard Hu of the University of Michigan made a research on 466 men aged around 67. Their mental abilities were tested twice, four years apart. Higher bone lead amounts were connected to a cognitive decline, similar to about five years of aging. "Nobody is claiming that lead is the sole cause of age-related mental decline, but it appears to be one of several factors involved," said Hu.
"If so, it would join such possible influences as high blood pressure, diabetes, stroke, emotional stress and maybe education level. Nobody knows exactly what causes mental decline with age," said Bradley Wise of the National Institute on Aging.
Researchers cannot explain the delayed effects of lead in the brain. Do the effects come from a moment's exposure, or does the lead in the bone harm over a lifetime, leaking continuously into the bloodstream?
"I think that both things are happening," said Schwartz.
"There's still lead in the environment, and exposure remains especially high in many developing countries. Women who grew up in the 1970s might dose their fetuses with the metal," said Hu, pointing to the fact that lead can cross the placenta.