Blood lead levels in relation to cognitive function in older U.S. adults

Studies suggest that cumulative exposure to lead, as measured in the bone, is associated with accelerated cognitive decline at older age. It is presently unclear, however, whether current blood lead levels (BLLs) are adversely related to cognitive functioning in older adults. We evaluated BLLs in relation to cognition in the continuous National Health and Nutrition Examination Survey (NHANES). The current study was limited to adults age 60 and older. We examined two measures of cognitive functioning: self-reported functional limitation due to difficulty remembering or periods of confusion (NHANES 1999-2008; n = 7277) and performance on the Digit Symbol Substitution Test (DSST; NHANES 1999-2002; n = 2299). We evaluated quintiles of BLL (<1.30, 1.79-<2.30, 2.30-<3.20, and ≥3.20 μg/dL) in relation to cognitive functioning using logistic (functional limitation) and linear (DSST scores) regression in SUDAAN, adjusting for age, sex, race, poverty-income ratio, education, and self-reported general health status. BLLs were not associated with self-reported confusion or memory problems in crude and adjusted analyses, with adjusted odds ratios and 95% confidence intervals (CI) of 1.0 (ref.), 0.9 (CI = 0.7-1.3), 0.8 (CI = 0.6-1.2), 1.0 (CI = 0.7-1.3), 1.0 (CI = 0.7-1.4), respectively, in increasing quintiles. Similarly, there was no clear association between performance on the DSST and BLL after accounting for all covariates. Our findings add to the inconsistent evidence regarding the association between concurrent BLLs and cognitive function in older adults. Early-life or long-term, accumulated lead exposures may be etiologically more relevant to accelerated cognitive decline at older age.