Several intriguing studies have found an association between exposure to lead and other pollutants early in life and the mental decline of older people. 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. It also means that some of the mental decline in older people, thought of as a “natural” consequence of aging, might be avoidable.
Virtually all Americans have lead in their blood, but the amounts are far lower today than in the past. That’s because the US began phasing out lead in gasoline from 1976 to 1991. Because of that and measures to eliminate lead in other products, the average lead level in the blood of American adults fell 30 percent by 1980 and about 80 percent by 1990. But several studies conducted by scientists at the University of Michigan indicate that some people might be suffering from lead exposure they experienced decades ago.
In 2006, researchers at Michigan 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. Bone scans were used to determine their lead levels. 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.
Another study conducted at the University of Michigan in 2004 looked at 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.
Studies of other pollutants have also found a link between exposure and age-related diseases. Studies on 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. For example, rodents that encounter PCBs or dioxins before birth are more susceptible to cancer once they grow up.
Nobody is claiming that lead or pollution exposure is the sole cause of age-related mental decline, but it appears to be one of several factors involved. Exactly how earlier lead exposure might lead to age-related mental impairment is not known. And no one has determined if anything can be done to help people who have absorbed a lot of lead over a lifetime.
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