Long-ago exposure may make brain work as if it's older
NEW YORK – Could it be that the "natural" mental decline that afflicts many older people is related to how much lead they absorbed decades before?
That's the provocative idea emerging from some recent studies, part of a broader area of research that suggests some pollutants cause harm that shows up only years after exposure.
The new work suggests long-ago lead exposure can make an aging person's brain work as if it's five years older than it really is. If that's verified by more research, it means that sharp cuts in environmental lead levels more than 20 years ago didn't stop its widespread effects.
"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," said Dr. Brian Schwartz of Johns Hopkins University.
"The fact that it's happening with lead is the first proof of principle that it's possible," said Dr. Schwartz, a leader in the study of lead's delayed effects. Other pollutants like mercury and pesticides may do the same thing, he said.
The notion of long-delayed effects is familiar – tobacco and asbestos, for example, can lead to cancer. But in recent years, scientists are coming to appreciate that exposure to other pollutants in early life also may promote disease much later on.
Hard to study
Studying delayed effects in people is difficult, because they generally must be followed for a long time. Research with lead is easier, because scientists can measure the amount that has accumulated in the shinbone over decades and get a read on how much lead a person has been exposed to.
Lead in the blood, by contrast, reflects recent exposure. Virtually all Americans have lead in their blood, but the amounts are far lower today than in the past.
The big reason for the drop: the phasing out of lead in gasoline from 1976 to 1991. Because of that and accompanying measures, the average lead level in the blood of American adults fell 30 percent by 1980 and about 80 percent by 1990.
That's a major success story for environmentalists. But work by Dr. Schwartz and Dr. Howard Hu of the University of Michigan suggests that the long-term effects of the high-lead era are still being felt.
In 2006, Dr. Schwartz and his colleagues published a study of about 1,000 Baltimore residents. They were ages 50 to 70, old enough to have absorbed plenty of lead before it disappeared from gasoline. They probably got their peak doses in the 1960s and 1970s, Dr. Schwartz said, mostly by inhaling air pollution from vehicle exhaust and from other environmental sources.
The researchers estimated each person's lifetime dose by scanning their shinbones for lead. Then they gave each one a battery of mental ability tests.
In brief, the scientists found that the higher the lifetime lead dose, the poorer the performance across a wide variety of mental functions, like verbal and visual memory and language ability. From low to high dose, the difference in mental functioning was about the equivalent of aging by two to six years.
Dr. Hu and his colleagues took a slightly different approach in a 2004 study of 466 men with an average age of 67. Those men took a mental-ability test twice, about four years apart on average. Those with the highest bone lead levels showed more decline between exams than those with smaller levels, with the effect of the lead equal to about five years of aging.
Other influences
Nobody is claiming that lead is the sole cause of age-related mental decline, but it appears to be one of several factors involved, Dr. Hu stressed.
If so, it would join such possible influences as high blood pressure, diabetes, stroke, emotional stress and maybe education level, said Bradley Wise of the National Institute on Aging. Nobody knows exactly what causes mental decline with age, he said.
Although the studies by Dr. Hu and Dr. Schwartz suggest lead is involved, Dr. Wise and others say they don't prove the link.
"I think many things impact how we age, but I think right now it's maybe premature to be giving lead a huge role in our age-related cognitive decline," said Dr. Margit L. Bleecker, director of the Center for Occupational and Environmental Neurology in Baltimore. Still, she called the lead hypothesis "a very interesting idea" deserving more study.
Others were more impressed.
"The new evidence from these studies should concern people," said epidemiologist Andrew Rowland of the University of New Mexico. "These two research groups are finding adverse effects on the aging brain at low levels of lead exposure. More work needs to be done, but these studies are raising important questions."
GASOLINE ISN'T ONLY DANGER
NEW YORK – Researchers are finding that lead absorbed early in life may affect brain function in old age. While some sources of lead, such as leaded gasoline have dropped, there are others. For example:
- Deteriorating lead paint can produce lead dust and chips that children swallow. The federal government banned lead paint from housing in 1978, but older homes may have it.
- Soil can become contaminated and be carried indoors.
- Drinking water can pick up lead from pipes or solder in older homes.
- Traces of lead can be brought home on hands or clothes from jobs that involve working with the metal.
- Food and liquids stored in lead crystal or lead-glazed containers may pick up the metal.
- Some folk remedies contain lead.
- Lead is used in some hobbies, such as making pottery or stained glass, or refinishing furniture.
Originally published on 1/27/2008 by Associated Press and shown on the shared content section of The Dallas Morning News website here.
