Historical cohort study of US man-made vitreous fiber production workers: I. 1992 fiberglass cohort follow-up: initial findings

Our plain-English summary of Historical cohort study of US man-made vitreous fiber production workers: I. 1992 fiberglass cohort follow-up: initial findings, by G.M. Marsh, A.O. Youk, R.A. Stone, et al (Journal of Occupational and Environmental Medicine, 2001).

The study

• Authors: G.M. Marsh, A.O. Youk, R.A. Stone, J.M. Buchanich, M.J. Gula, T.J. Smith, M.M. Quinn
• Journal: Journal of Occupational and Environmental Medicine
• Published: 2001;43(9):741-56
• Cited by: 51 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

This 1986 to 1992 update and expansion of an earlier historical cohort study examined the 1946 to 1992 mortality experience of 32,110 workers employed for 1 year or more during 1945 to 1978 at any of 10 US fiberglass (FG) manufacturing plants. Included are (1) a new historical exposure reconstruction for respirable glass fibers and several co-exposures (arsenic, asbestos, asphalt, epoxy, formaldehyde, polycyclic aromatic hydrocarbons, phenolics, silica, styrene, and urea); and (2) a nested, matched case-control study of 631 respiratory system cancer (RSC) deaths in male workers during 1970 to 1992 with interview data on tobacco smoking history. Our findings to date from external comparisons based on standardized mortality ratios (SMRs) in the cohort study provide no evidence of excess mortality risk from all causes combined, all cancers combined, and non-malignant respiratory disease. Also, excluding RSC, we observed no evidence of excess mortality risk from any of the other cause-of-death categories considered. For RSC among the total cohort, we observed a 6% excess (P = 0.05) based on 874 deaths. Among long-term workers (5 or more years of employment) we observed a not statistically significant 3% excess based on 496 deaths. Among the total cohort, we observed increases in RSC SMRs with calendar time and time since first employment, but these were less pronounced among long-term workers. RSC SMRs were not related to duration of employment among the total cohort or long-term workers. In an externally controlled analysis of male workers at risk between 1970 and 1992, we observed no association between RSC SMRs and increasing exposure to respirable FG. Our findings to date from internal comparisons based on rate ratios in the case-control study of RSC were limited to analyses of categorized study variables with and without adjustment for smoking. On the basis of these analyses, the duration of exposure and cumulative exposure to respirable FG at the levels encountered at the study plants did not appear to be associated with an increased risk of RSC. RSC risk also did not seem to increase with time since first employment. There is some evidence of elevated RSC risk associated with non-baseline levels of average intensity of exposure to respirable glass, but when adjusted for smoking this was not statistically significant, and there was no apparent trend with increasing exposure. This same pattern of findings was observed for duration of exposure, cumulative exposure, and average intensity of exposure to formaldehyde. None of the other individual co-exposures encountered in the study plants appeared to be associated with an increased risk of RSC. The primary focus of ongoing analyses is to determine the extent to which our present findings are robust to alternative characterizations of exposure.

In plain English

This historical cohort update followed deaths from 1946 to 1992 among 32,110 workers employed at least 1 year during 1945 to 1978 at 10 US fiberglass plants (6 months for some men at plants 6 and 10; from 1940 at plant 9). Men dying of respiratory system cancer during 1970 to 1992 were compared with matched controls, using interviewed smoking histories. Against local rates, the respiratory system cancer standardized mortality ratio was 1.06 (95% CI 1.00 to 1.14; 874 deaths), and 1.03 (95% CI 0.94 to 1.12; 496 deaths) among those employed 5 or more years. Ever-smokers' risk of respiratory cancer death was 13.2-fold that of never-smokers (95% CI 7.08 to 24.58). Smoking-adjusted risk ratios were 1.61 (95% CI 1.02 to 2.57) for possible formaldehyde exposure, without significant trend, and 1.03 (95% CI 0.79 to 1.35) for possible asbestos exposure (0.98 unadjusted; 95% CI 0.77 to 1.25). The authors said the asbestos result may reflect misclassification or very low exposure. They concluded that duration and cumulative respirable fiberglass exposure, at the plants' levels, did not appear associated with increased respiratory cancer risk.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Historical cohort mortality study (update and expansion of an earlier cohort), with a nested, matched case-control study of respiratory system cancer deaths among male workers
• Who was studied: 32,110 production or maintenance workers employed for at least 1 year between 1945 and 1978 at 10 US fiberglass manufacturing plants, with mortality followed 1946 to 1992. There were two exceptions: a 6-month employment criterion for male workers in the original cohort from plants 6 and 10, and a 1940 starting date for plant 9. The case-control study covered male workers who died of respiratory system cancer during 1970 to 1992; the analysis included 631 cases and 570 controls.
• Exposure: Respirable glass fibers, formaldehyde and silica were estimated quantitatively. Arsenic, asbestos, asphalt, epoxy, polycyclic aromatic hydrocarbons, phenolics, styrene and urea were assigned qualitatively, meaning only that potential exposure existed.
• Main results:
  • Total cohort, all causes: 9,173 deaths, SMR 0.92 (95% CI 0.90 to 0.93) against US rates. Against local county rates: 8,436 deaths, SMR 0.90 (95% CI 0.88 to 0.92).
  • Total cohort, non-malignant respiratory disease against local rates: SMR 0.86 (95% CI 0.79 to 0.93), a deficit.
  • Total cohort, respiratory system cancer: 874 deaths. SMR 1.16 (95% CI 1.08 to 1.24) against US rates; SMR 1.06 (95% CI 1.00 to 1.14) against local county rates.
  • Respiratory system cancer by worker type (local rates): short-term workers (under 5 years) 378 deaths, SMR 1.12 (95% CI 1.01 to 1.24). Long-term workers (5 or more years) 496 deaths, SMR 1.03 (95% CI 0.94 to 1.12), not statistically significant.
  • Case-control study of respiratory system cancer mortality: ever-smokers (609 cases) had an RR of 13.20 (95% CI 7.08 to 24.58) compared with never-smokers.
  • Case-control study, workers potentially exposed to respirable fibers: RR 1.79 (95% CI 0.77 to 4.14), based on only nine unexposed cases, not statistically significant. After smoking adjustment: RR 1.37 (95% CI 0.55 to 3.42).
  • Case-control study, cumulative respirable fiber exposure: no adjusted risk ratio was statistically significantly elevated, and no global test was statistically significant.
  • Case-control study, average intensity of respirable glass fiber exposure: some evidence of elevated risk at non-baseline levels. This was not statistically significant after smoking adjustment, and there was no apparent trend.
  • Case-control study, workers potentially exposed to formaldehyde (591 cases): RR 1.92 (95% CI 1.25 to 2.94) unadjusted; RR 1.61 (95% CI 1.02 to 2.57) adjusted for smoking.
  • Formaldehyde: trend tests in the adjusted models were not statistically significant for any of the exposure measures.
  • Case-control study, workers potentially exposed to asbestos (255 cases): RR 0.98 (95% CI 0.77 to 1.25) unadjusted; RR 1.03 (95% CI 0.79 to 1.35) adjusted for smoking.
• The authors' conclusion: The authors concluded that duration and cumulative exposure to respirable fiberglass, at the levels encountered at the study plants, did not appear to be associated with an increased risk of respiratory system cancer.
• Limitations the authors state:
  • The authors stated that at least part of the respiratory system cancer excess seen in the SMR comparisons is probably due to confounding by tobacco smoking.
  • The authors stated that the absence of elevated risk for arsenic and asbestos may reflect exposure misclassification and/or very low exposure levels in the plants studied.
  • The authors noted that nearly half the cohort worked less than 5 years at the plants, which contributed to generally low estimated exposures.
  • The case-control findings so far were limited to analyses of categorized variables, with and without smoking adjustment.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer.

Medical terms in this study, explained in our Lexicon: Cohort Study, Vitreous, Exposure Reconstruction, Case-Control Study, standardized mortality ratio (SMR), rate ratio, Cumulative Exposure.

Related studies

• Historical cohort study of US man-made vitreous fiber production workers: II. Mortality from mesothelioma — G.M. Marsh, M.J. Gula, et al. (2001)
• Mortality among a cohort of US man-made mineral fiber workers: 1985 follow-up — G.M. Marsh, P.E. Enterline, et al. (1990)
• Man-made vitreous fibers and risk of respiratory system cancer: a review of the epidemiologic evidence — I.M. Lee, C.H. Hennekens, et al. (1995)
• Lung cancer and exposure to man-made vitreous fibers: results from a pooled case-control study in Germany — H. Pohlabeln, K.H. Jöckel, et al. (2000)
• Difficulties of attribution of effect in workers exposed to fiberglass and asbestos — K.H. Kilburn, R.H. Warshaw (1991)
• Respiratory cancer and exposure to man-made vitreous fibers: a systematic review — D. Berrigan (2002)

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