Several studies have linked silica exposure to renal disease (particularly glomerulonephritis) and rheumatoid arthritis, but these associations are still not widely accepted. Approximately 2 million people are occupationally exposed to silica in the U.S. We studied 4620 workers exposed to silica in the industrial sand industry. We found an excess of mortality from acute renal disease (SMR 2.61, 95% CI 1.49-4.24, 16 deaths), chronic renal disease (SMR 1.61 (95% CI 1.13-2.22, 36 deaths), and arthritis (SMR 4.36,95% CI 2.76-6.54, 23 deaths) based on multiple cause mortality data (any mention on a death certificate). A large excess of mortality ty from silicosis was also seen (SMR 18.2,95% CI 10.6-29.1, 17 deaths). Linking the cohort with the U.S. registry of end stage renal disease (ESRD) cases for 1977-1996, we found a two-fold excess of ESRD (rate ratio 1.97,95% CI 1.25-2.96,23 cases), concentrated in glomerulonephritis (rate ratio 3.85, 95% CI 1.55-7.93, 7 cases). A job-exposure matrix based on over 4000 industrial hygiene samples was used to estimate silica exposures over time. We found a positive trend between ESRD and cumulative exposure (p = .01); the rate ratio for the highest quartile of exposure versus the U.S. population was 3.82 (95 % CI 1.24-8.91). A male exposed at the NIOSH Recommended Exposure Level (0.05 mg/m3) is estimated to have a lifetime risk of ESRD of 13%; the background risk for a nonexposed male is 2%. In nested case-control analyses, a positive exposure- response was observed for rheumatoid arthritis mortality (p = .04), but not for other types of arthritis. These data represent the largest number of kidney disease cases analyzed to date in a cohort with well-defined silica exposure, and suggest a causal link between silica and kidney disease. The results for arthritis are also suggestive, but based on smaller numbers.
American Journal of Epidemiology, Abstracts of the 33rd Annual Meeting of the Society for Epidemiologic Research, Seattle, Washington, June 15-17, 2000