Blood lead, blood manganese, and grip strength in older U.S. adults: NHANES 2011-2012

Environmental exposure to toxic metals is a major public health issue. Neurological impact caused by low concentrations of lead (Pb) and manganese (Mn), is still not well understood. National Health and Nutrition Examination Survey (NHANES) 2011-2012 data was used to test the hypothesis that blood Pb (BPb), blood Mn (BMn), or both, may have a significant impact on grip strength, a marker of neuromotor function. This cross-sectional analysis included 1286 individuals ≥60 years old with complete data on confounders. Blood metals, indicators of recent exposure, were analyzed using ICP-MS and natural-log transformed for statistical analysis. Grip strength was collected using a handgrip dynamometer. Analysis included appropriate survey weights and linearized standard errors.  Adjusted multivariable linear regression models controlled for age, sex, race/ethnicity, education, blood cotinine and body mass index (BMI). Geometric mean BPb and BMn were 1.55µg/dL (95% Confidence Interval (C.I.): 1.44, 1.68) and 8.75µg/L (95% C.I.: 8.53, 8.98), respectively. In adjusted models, decreased grip strength was significantly associated with increasing BPb (β= -1.40; 95% C.I.: -2.54, -0.26) but not BMn (β= -1.31; 95% C.I.: -4.36, 1.73). BPb, but not BMn, was significant in a model controlling for both metals; there was no evidence of a statistical interaction. These results suggest that increasing BPb levels are associated with decreasing grip strength. However, as neurologic function may be the result of exposures occurring over a lifetime, we recommend that future studies incorporate use of cumulative exposure markers such as bone lead and manganese.