Baseline serum β-carotene concentration and mortality among long-term asbestos-exposed insulators

Our plain-English summary of Baseline serum β-carotene concentration and mortality among long-term asbestos-exposed insulators, by D. Hashim, D. Gaughan, P. Boffetta, et al (Cancer Epidemiology, Biomarkers & Prevention, 2015).

The study

• Authors: D. Hashim, D. Gaughan, P. Boffetta, R.G. Lucchini
• Journal: Cancer Epidemiology, Biomarkers & Prevention
• Published: 2015;24(3):555-60
• Cited by: 13 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: Although interventional trials demonstrated that moderate-dose β-carotene supplementation increases lung cancer mortality in smokers and asbestos-exposed workers, differences in serum concentrations in absence of supplementation have not been studied in asbestos-exposed workers.

Methods: A mortality analysis was performed to assess the relationship of nonsupplemented serum β-carotene to all-cause and cancer mortalities using 1981 to 1983 serum β-carotene concentration measurements from 2,646 U.S. white male insulators (mean age, 57.7 years). Multivariable-adjusted Cox proportional hazard models that included terms for age, duration of asbestos exposure, smoking, season, and region were fitted to estimate mortality HRs and 95% confidence intervals (CI) according to serum β-carotene concentrations.

Results: Median follow-up was 12.8 years and 984 (33.8%) subjects died during the follow-up period, including 415 deaths from overall cancer and 219 deaths from lung cancer. The overall mortality HR for a serum β-carotene increase of 10 μg/dL was 0.97 (95% CI, 0.96-0.99). Compared with the lowest quartile, HRs were 0.90 (95% CI, 0.76-1.07) for the second (38-65 μg/dL), 0.80 (95% CI, 0.67-0.96) for the third (66-104 μg/dL), and 0.63 (95% CI, 0.51-0.77) for the highest serum β-carotene quartile (≥105 μg/dL). There was no association between serum β-carotene and overall cancer mortality (HR, 1.00; 95% CI, 0.97-1.02) or lung cancer mortality (HR, 0.99; 95% CI, 0.96-1.02).

Conclusions: Higher nonsupplemented serum β-carotene concentrations were negatively associated with all-cause mortality among asbestos-exposed individuals.

Impact: Serum β-carotene can be a marker of one or more determinants of reduced mortality in asbestos-exposed workers. Cancer Epidemiol Biomarkers Prev; 24(3); 555-60. ©2014 AACR.

©2014 American Association for Cancer Research.

In plain English

This study looked at whether blood (serum) levels of β-carotene were linked to death rates among men with long-term asbestos exposure. The authors used archived data on 2,646 US white male asbestos insulators from the North American Insulator Cohort who were examined in 1981 to 1983. Men who had taken β-carotene supplements were excluded. The men had been exposed to mixed asbestos fiber types, mainly chrysotile. Over a median follow-up of 12.8 years, 984 men died, 415 of them from cancer. After adjustment for age, years of insulation work, smoking, season and region, each 10 µg/dL higher β-carotene level was associated with a hazard ratio for death from any cause of 0.97 (95% CI 0.96 to 0.99). The highest quarter (105 µg/dL or more) had a hazard ratio of 0.63 (0.51 to 0.77) compared with the lowest quarter. No statistically significant association was found with deaths from all cancers, lung cancer, mesothelioma or colon cancer. The authors concluded that higher β-carotene was associated with lower overall mortality. They said confounding by lifestyle factors could not be ruled out.

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: Mortality analysis of an existing occupational cohort, using archived examination data (serum β-carotene measured once at baseline) and Cox proportional hazards models
• Who was studied: 2,646 US white male asbestos insulators (union members in the North American Insulator Cohort) with complete data, out of 2,907 examined in 19 US cities from November 1981 to November 1983. Workers who had taken β-carotene supplements were excluded. Mortality was followed to January 7, 1996, with a median follow-up of 12.8 years.
• Exposure: Occupational asbestos exposure as insulators, to mixed fiber types, predominantly chrysotile, measured as years of insulation work (median 33.0 years). The variable studied was non-supplemented serum β-carotene concentration, presumed to be in µg/dL.
• Main results:
  • All insulators, all-cause mortality: hazard ratio per 10 µg/dL increase in serum β-carotene was 0.97 (95% CI 0.96, 0.99) when adjusted for age, years of insulation work, smoking status, season and region.
  • All insulators, all-cause mortality: per 10 µg/dL increase, hazard ratio was 0.981 (95% CI 0.969, 0.994) when adjusted only for age, years of insulation work and smoking status.
  • All-cause mortality, second quartile (38-65 µg/dL) vs lowest quartile, fully adjusted model: hazard ratio 0.90 (95% CI 0.76, 1.07).
  • All-cause mortality, third quartile (66-104 µg/dL) vs lowest quartile, fully adjusted model: hazard ratio 0.80 (95% CI 0.67, 0.96).
  • All-cause mortality, highest quartile (105 µg/dL or more) vs lowest quartile (below 38 µg/dL): hazard ratio 0.71 (95% CI 0.59, 0.85) adjusted for age, insulation work duration and smoking (29% lower risk). With season and region added, the hazard ratio was 0.63 (95% CI 0.51, 0.77), or 37% lower risk. The quartiles had 288 deaths (lowest) and 202 deaths (highest).
  • Among the 886 current smokers at baseline, all-cause mortality hazard ratio per 10 µg/dL increase, adjusted for pack-years, was 0.967 (95% CI 0.943, 0.992).
  • Among past smokers, the hazard ratio per 10 µg/dL increase, adjusted for pack-years and years since quitting, was 0.985 (95% CI 0.968, 1.003), which was not statistically significant.
  • No significant effect modification of the all-cause mortality association was found by baseline age, duration of insulation work or smoking status.
  • Of 984 deaths, 415 were from cancer: 219 lung cancer, 104 mesothelioma and 17 colon cancer. There were no statistically significant associations of serum β-carotene with deaths from all cancers combined or from these specific cancers.
• The authors' conclusion: The authors concluded that higher baseline serum β-carotene concentrations were associated with decreased mortality in asbestos-exposed insulators. No association was found for all cancers combined, lung cancer, mesothelioma or colon cancer. In their view, serum β-carotene can be a marker of one or more determinants of reduced all-cause mortality in this population.
• Limitations the authors state:
  • The favorable association could be due to confounding lifestyle factors.
  • There were no data on other nutrients, diet, body mass index or cholesterol.
  • Serum β-carotene was measured only once, so dietary changes during follow-up could not be assessed.
  • Asbestos exposure was measured only as duration, and all workers were assumed to have the same intensity of exposure.
  • Most workers had long exposure durations, so the data may not have allowed accurate assessment of effect modification between high and low asbestos exposure.
  • Original measurement documentation was unavailable, so the units (µg/dL) were presumed from the range of values.
  • Small numbers for some cancers prevented stable quartile-based hazard ratios.

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: Insulator, Lung Cancer, Asbestos Exposure, confidence interval, Biomarker.

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• The Beta-Carotene and Retinol Efficacy Trial: incidence of lung cancer and cardiovascular disease mortality during 6-year follow-up after stopping beta-carotene and retinol supplements — G.E. Goodman, M.D. Thornquist, et al. (2004)
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