Navy Asbestos Medical Surveillance Program (1991-1999): linear regression analysis for the effect of asbestos exposure on pulmonary function testing

Our plain-English summary of Navy Asbestos Medical Surveillance Program (1991-1999): linear regression analysis for the effect of asbestos exposure on pulmonary function testing, by B.K. Bohnker, L.S. Betts, D.M. Sack, et al (Military Medicine, 2004).

The study

• Authors: B.K. Bohnker, L.S. Betts, D.M. Sack, N. Craft
• Journal: Military Medicine
• Published: 2004;169(8):620-6
• Cited by: 4 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The effect of asbestos exposure on pulmonary function was studied using data from the Navy Asbestos Medical Surveillance Program. Records were selected for Caucasian men from 1991 to 1999 (N = 89,318) and were analyzed using a cross-sectional, linear regression model. Dependent variables were forced expiratory volume in 1 s (FEV1) and forced vital capacity (FVC), with independent continuous variables of age, height, weight, smoking, and asbestos history. Overall, the continuous variable for asbestos exposure demonstrated significant protection of +1.1 cm3/year (t = 3.278, p = 0.001) for FEV1 and +1.6 cm3/year (t = 4.225, p = 0.000) for FVC. There was significant interaction between asbestos exposure and smoking history (FEV1, -0.09 cm3/year2, t = -6.467, p = 0.000; FVC, -0.097 cm3/year2, t = -5.663, p = 0.000). This study suggests that workers within the program demonstrated minimal additional pulmonary function changes during the period, particularly if they do not smoke tobacco. The study also supports continuing smoking cessation efforts for all asbestos-exposed workers.

In plain English

This study used U.S. Navy Asbestos Medical Surveillance Program records, which follow workers with potential asbestos exposure. The authors ran a cross-sectional linear regression on 89,318 examination records from Caucasian men aged 30 to 60, dated 1991 to 1999. They related self-reported years of asbestos exposure to two breathing-test measures, FEV1 and FVC, adjusting for age, height, weight, smoking and examination year. With all exposure categories combined, the asbestos coefficient was slightly positive, which the authors called slightly protective: 1.065 cubic centimeters per exposure-year for FEV1 and 1.622 for FVC. However, the model also showed a significant negative asbestos-smoking interaction, which the authors said overcomes this apparent protective effect. This interaction appeared overall and in the previous and indirect exposure groups, but not in the direct group. For men with current direct exposure compared with unexposed men, asbestos exposure was not significantly linked to either measure. The authors concluded that the asbestos coefficients were small and either not statistically significant or slightly protective. They noted that exposure was self-reported, that respirator use was not considered, and that the design was unlikely to assess cancers such as mesothelioma.

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: Population-based cross-sectional analysis of surveillance records using linear regression
• Who was studied: 89,318 examination records from Caucasian men aged 30 to 60 in the U.S. Navy Asbestos Medical Surveillance Program, 1991 to 1999. These are records, not necessarily separate individuals: many personnel had multiple examinations.
• Exposure: Self-reported years of asbestos exposure in the workspace, with self-reported categories of none, direct, indirect and previous exposure. There were no measured exposure data and no fiber type was given. Asbestos on Navy ships and shore structures was used in insulating and friction materials.
• Main results:
  • All exposure categories combined: the asbestos exposure coefficient was slightly protective, 1.065 cm3 per year for FEV1 (t 3.278, p 0.001) and 1.622 cm3 per year for FVC (t 4.225, p 0.000). The model also included a negative asbestos-smoking interaction, which the authors said overcomes this apparent protective effect, so the coefficient is not a uniform effect for all workers.
  • The authors wrote that the negative asbestos-smoking interaction overcomes the apparent protective effect of asbestos exposure.
  • There was a significant negative interaction between smoking and asbestos exposure, with magnitudes of 0.094 cm3 per year squared for FEV1 and 0.097 for FVC overall. The interaction was seen in the overall, previous and indirect exposure analyses, but not in the current direct exposure group.
  • None plus previous exposure: asbestos exposure was not significantly associated with FEV1 (0.834 cm3 per year, p 0.080). There was a weakly protective association with FVC (1.275 cm3 per year, p 0.023).
  • None plus current direct exposure: asbestos exposure was not significantly associated with FEV1 or FVC, and there was no significant interaction with smoking.
  • None plus current indirect exposure: asbestos exposure was significantly associated with a protective effect for FEV1 (2.645 cm3 per year, p 0.000) and FVC (2.851 cm3 per year, p 0.000).
  • The coefficient for year of examination was statistically significant and protective throughout the analysis.
• The authors' conclusion: The authors concluded that, with asbestos exposure treated as a continuous variable, its coefficients were small and either not statistically significant or slightly protective. They also found a statistically significant negative interaction between smoking and asbestos exposure.
• Limitations the authors state:
  • Exposure intensity was categorized without considering the protective effect of respirator use.
  • Measured exposure data were unavailable. Self-reported years of exposure were used instead, which could introduce several kinds of bias.
  • The difference between direct and indirect exposure could not be quantified, which may have reduced any effect found.
  • The design was unlikely to assess very long-term effects such as mesothelioma or lung cancers.
  • The results may not apply to populations with different fiber types or different respiratory protection.
  • Military and civilian workers were not analyzed separately.
  • The cohort was not analyzed for retention or for disease progression in individuals.

Topics

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

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, FEV1.

Related studies

• Navy Asbestos Medical Surveillance Program (1984-1990): linear regression analysis for effect of asbestos exposure on pulmonary function testing — B.K. Bohnker, L.S. Betts, et al. (2004)
• Variability in interpretation among B-readers in the U.S. Navy Asbestos Medical Surveillance Program — J.G. Muller, J.M. Lieske, et al. (2008)
• Navy Asbestos Medical Surveillance Program 1990-1999: demographic features and trends in abnormal radiographic findings — D.M. Dell, B.K. Bohnker, et al. (2006)
• Changes in B-readings over time in the United States Navy Asbestos Medical Surveillance Program — J.G. Muller, W.G. Rudolph, et al. (2007)
• Trends in pleural radiographic findings in the Navy Asbestos Medical Surveillance Program (1990-1999) — J.G. Muller, B.K. Bohnker, et al. (2005)
• Evaluation of the national health surveillance program of workers previously exposed to asbestos in Spain (2008) — M.G. Gómez, R. Castañeda, et al. (2012)

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