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Exposure to lead-contaminated drinking water in childhood was tied to lower levels of cognition in late adulthood, U.S. data showed.

Older adults who lived as children in cities with lead pipes and acidic or alkaline water that would leach it had lower cognitive functioning at age 72 than others (β -0.408, P<0.01), reported Haena Lee, PhD, of the University in Southern California in Los Angeles, and colleagues.

The association between childhood lead exposure and adult cognitive function equaled the effect of 8 additional years of aging, Lee and co-authors wrote in . The overall relationship between childhood lead exposure and adult cognition persisted after adjusting for education, income, wealth, and cardiovascular health.

"Americans who are now in their 40s and 50s experienced more lead exposure as children than any other generation," noted co-author John Robert Warren, PhD, of the University of Minnesota in Minneapolis. "Those who are now middle-aged or older were exposed as children to high levels of lead in drinking water, paint, car exhaust, and elsewhere," he told MedPage Today.

While considerable research has focused on lead's effects on kids and the effects of adult lead exposure on adult cognition, "no prior research has documented the long-term consequences of childhood lead exposure for later-life cognitive outcomes in a large, diverse, community-based sample of Americans," Warren stated.

The study evaluated 1,089 participants from 12 waves of the ongoing (HRS) from 1998 to 2016, matching them to their childhood household records from the 1940 U.S. Census. About 51% of participants were female, and 89% of participants were white.

The researchers classified participants from cities with lead municipal pipes and acidic or alkaline water -- conditions necessary for lead to leach into drinking water -- as exposed. Remaining participants were considered unexposed.

Overall, 77 participants would have been exposed to lead pipes and either acidic or alkaline water in childhood, 394 had lead pipes and neutral water, and 618 were in cities without lead service lines.

HRS participants took three cognitive tests from 1998 to 2016. While childhood lead exposure was tied to lower levels of cognition in late adulthood, it was not necessarily associated with a steeper rate of cognitive decline.

About a quarter of the association between lead-contaminated water and later-life cognition was accounted for by educational attainment. Income, wealth, stroke, hypertension, and heart disease did not substantially mediate the relationship between childhood lead exposure and adult cognitive function.

"Our research shows -- contrary to some hypotheses -- that it is not the case that the effects of childhood lead exposure on adult cognition operate mainly through education and adult socioeconomic position," Warren said.

"Instead, much of the effect may operate more directly," he continued. "Our findings at least partially support the idea that quantities of lead ingested in childhood are stored in the bones and re-emerge late in life when bones demineralize because of osteoporosis or other causes."

The study comes with caveats, the researchers acknowledged. Generalizability may be limited to people cognitively intact when they enrolled in the HRS cohort. Studying only tap water exposure excluded lead exposure through other pathways like leaded gasoline and paint. In addition, unknown variables may have influenced results.

Within the next 10 years, American children exposed to high levels of lead during the 1970s will enter older ages, Warren noted. "This means that the consequences for cognition of adolescent exposure to lead may be felt most heavily in the decades ahead," he said.

"This research highlights the continuing need for reducing lifetime -- and especially childhood -- lead exposure," Warren added. "It also highlights the need for early screening for cognitive problems."

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