Thanks to our several generations of stupidity and neglect, the most persistent and dangerous environmental hazard in America is still lead poisoning. Our usual attention is on damage to fetuses and children, but now comes an important public health study that tells us with hard evidence that cumulative lead exposure at ordinary community levels is associated with significant cognitive decline in older women (Weuve et al. Environmental Health Perspectives. 2009. 117(4):574-580).
The authors of the study (17 people at Harvard University, University of Michigan, and Rush University Medical Center in Chicago) are unequivocal in their conclusion: "These findings suggest that cumulative exposure to lead, even at low levels experienced in community settings, may have adverse consequence for women's cognition in older age."
The study involved measurements of both bone lead and blood lead levels in 587 women 47 to 74 years of age.
Bone lead (patella and tibia lead in this study) is essentially a measure of cumulative exposure, while blood lead is essentially a measure of recent exposure. The difference in measures is due to the fact that most lead sooner or later is sequestered in bone, where it accumulates, and from where it's later released as a doppelganger for calcium. When lead gets into the brain, early or late, it's a powerful neurotoxin in very low concentrations.
Ten years were spent in cognitive assessments of the women in this study. The authors are established investigators in their field, and the results need to be taken seriously by the public.
The important correlations in this study are with tibia bone lead. Concerning the magnitude of the cognitive deficits, the authors state: "The average decrement in cognitive test scores we observed for each standard deviation increase in tibia lead corresponded to the decrement in scores we observed for each 3-year increase in age among women in our study."
In plain language: the more lead in your bones, the faster your cognitive decline.
This is the first study of its kind specific to women. Women typically have lower lead exposures than men, but this study shows that even among women, cumulative lead exposure may adversely affect cognitive function. Impaired cognitive function is a strong risk factor for dementia--and women have a higher lifetime risk of developing dementia.
It's true that lead levels in the environment have fallen drastically in the past several decades, but older adults have been accumulating lead in their bones for many years, and if and when the lead in bone is released by metabolism in old age, the brain will be poisoned.
The authors point out that regulatory intervention and consequent widespread reductions in lead exposure "could have a substantial impact on the burden of cognitive impairment in the population."
This is science. In science you base your conclusions on the facts and observations at hand, with the reservation that tomorrow you may need to change your mind when new facts and new observations suddenly appear. Meanwhile, unregulated contamination of our environment continues to rot your brain and the brains of your children. We do need some changes in our attitudes.