Does low-level lead exposure increase risk of death? A mortality study of newspaper printers.

This exploratory study examined the mortality experience of a cohort of newspaper printers in order to investigate the effects of low-level exposure to lead. In this industry, historic lead exposure levels have been below the current US permissible exposure level (PEL) of 50 micrograms/m3. The study population was 1261 typesetters, employed in 1961 and followed until the end of 1984; this was a cohort of convenience, assembled as a comparison for a different study. Standardized mortality ratios (SMRs) were calculated using New York City comparison rates. The all-cause SMR was 0.74, and was significantly different from 1.00. Other statistically significant deficits were deaths from arteriosclerotic heart disease (SMR = 0.63) and non-malignant diseases of the respiratory system (SMR = 0.57) and digestive system (SMR = 0.65). These can be attributed to the comparison bias known as the healthy worker effect. The SMR for cerebrovascular disease (CVD) was 1.35, on the edge of statistical significance (95% confidence interval (CI): 0.98-1.82). When the cohort was stratified by years of union membership, a surrogate for length of exposure, only one cause of death was significantly elevated. For those printers employed for 30 years or more, the CVD SMR was 1.68 (95% CI: 1.18-2.31; p = 0.002). No significant excesses were seen for any other cause of death in any exposure stratum. Several studies of workers with much higher levels of lead exposure have reported elevated CVD risk. These findings suggest the possibility that lead exposure at levels below the current US PEL may also be associated with CVD mortality.