ABSTRACT
Group means from nerve conduction studies of persons exposed to lead were used in a meta-analysis. Differences between the control and exposed groups, and the slopes between nerve conduction measurements and log(10) blood lead concentrations were estimated using mixed models. Conduction velocity was reduced in the median, ulnar, and radial nerves in the arm, and in the deep peroneal nerve in the leg. Distal latencies of the median, ulnar, and deep peroneal nerves were longer. No changes in the amplitudes of compound muscle or nerve action potentials were detected. The lowest concentration at which a relationship with blood lead could be detected was 33.0 microg/dl for the nerve conduction velocity of the median sensory nerve. Lead may reduce nerve conduction velocity by acting directly on peripheral nerves or by acting indirectly, for example, on the kidney or liver.
Subject(s)
Lead Poisoning/diagnosis , Neural Conduction/drug effects , Occupational Diseases/chemically induced , Occupational Exposure/adverse effects , Adult , Aged , Dose-Response Relationship, Drug , Female , Humans , Lead Poisoning/physiopathology , Male , Median Nerve/drug effects , Median Nerve/physiopathology , Middle Aged , Neural Conduction/physiology , Occupational Diseases/physiopathology , Peroneal Nerve/drug effects , Peroneal Nerve/physiopathology , Radial Nerve/drug effects , Radial Nerve/physiopathology , Ulnar Nerve/drug effects , Ulnar Nerve/physiopathologyABSTRACT
OBJECTIVES: The goals of this study were two-fold: (1) to assess the relationship between blood lead levels and neurobehavioral test performance in a nationally sample of adults from the third National Health and Nutrition Evaluation Survey and (2) to analyze the results from previously published studies of occupational lead exposure that used the same neurobehavioral tests as those included in the survey. METHODS: Regression models were used to test and estimate the relationships between measurements of blood lead and performance on a simple reaction time, a symbol-digit substitution, and a serial digit learning test in adults aged 20-59 years who participated the survey. Mixed models were used to analyze the data from the occupational studies. RESULTS: The blood lead levels of those participating in the survey ranged from 0.7 to 41.8 microg/dl. The estimated geometric mean was 2.51 microg/dl, and the estimated arithmetic mean was 3.30 microg/dl. In the survey, no statistically significant relationships were found between blood lead concentration and performance on the three neurobehavioral tests when adjusted for covariates. In the occupational studies, the groups exposed to lead consistently performed worse than control groups on the simple reaction time and digit-symbol substitution tests. CONCLUSIONS: The results from the survey and the occupational studies do not provide evidence for impairment of neurobehavioral test performance at levels below 25 microg/dl, the concentration that the Centers for Disease Control and Prevention define as elevated in adults. The average blood lead level of the exposed groups in the occupational studies was 41.07 microg/dl, less than 50 microg/dl, the minimum concentration that the Occupational Safety and Health Administration requires for medical removal from the workplace. Given the evidence of impaired neurobehavioral performance in these groups, the 50 microg/dl limit should be reevaluated.
