Encouraging Health

‘Natural’ mental decline may be related to pollutants absorbed years before

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 new research that suggests some pollutants can cause harm that shows up only years after someone is exposed.

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.

Long-delayed effects
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.

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, he said. Only then would symptoms like forgetfulness or tremors appear.

Linda Birnbaum, director of experimental toxicology at the U.S. Environmental Protection Agency, said 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.

Animal studies also show clear evidence that being exposed to harmful substances in the womb can harm health later on, she said. For example, rodents that encounter PCBs or dioxins before birth are more susceptible to cancer once they grow up.

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.

Scary thought.

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lead exposure, mental decline

lead exposure, mental decline