The protective effect of beta-carotene and retinol on ventilatory function in an asbestos-exposed cohort

Our plain-English summary of The protective effect of beta-carotene and retinol on ventilatory function in an asbestos-exposed cohort, by P. Chuwers, S. Barnhart, P. Blanc, et al (American Journal of Respiratory and Critical Care Medicine, 1997).

The study

• Authors: P. Chuwers, S. Barnhart, P. Blanc, C.A. Brodkin, M. Cullen, T. Kelly, J. Keogh, G. Omenn, J. Williams, J.R. Balmes
• Journal: American Journal of Respiratory and Critical Care Medicine
• Published: 1997;155(3):1066-71
• Cited by: 53 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The association between serum beta-carotene or retinol concentration and level of ventilatory function was investigated in a population of asbestos-exposed men with a high rate of current and former cigarette smoking. The study population consisted of 816 subjects enrolled in the pilot component of the Carotene and Retinol Efficacy Trial (CARET), a placebo-controlled trial of supplemental beta-carotene and retinyl palmitate for the chemoprevention of lung cancer. Data available for analysis included baseline questionnaire, spirometry, chest X-ray, food frequency questionnaire, and serum beta-carotene and retinol concentrations. Serum beta-carotene concentration was associated with FEV1 (p < 0.05) and FVC (p < 0.05), with an approximately 100-ml increase over predicted values associated with raising the serum concentration from the 25th to the 75th percentile of the distribution in the study population (absolute difference = 155 ng/ml), even after adjustment for the confounding effects of asbestos exposure and cigarette smoking. Raising the serum retinol concentration from the 25th to the 75th percentile (absolute difference = 211 ng/ml) was associated with an approximately 70 ml increase in FVC (p < 0.05) over the predicted value. These results provide support for the hypothesis that beta-carotene and retinol have a protective effect on loss of ventilatory function.

In plain English

This cross-sectional study used enrollment data, collected before any trial vitamins were given, from 816 men aged 45 to 74 with past occupational asbestos exposure. They were in the pilot phase of the Carotene and Retinol Efficacy Trial (CARET) and enrolled in the Seattle area from 1985 to 1988. Of these, 798 had usable data, and most were current or former smokers. The authors compared blood levels of beta-carotene and retinol (vitamin A) with two lung function measures, FEV1 and FVC. Men with more chest X-ray changes consistent with asbestosis had lower levels of both vitamins, and smokers had lower beta-carotene. After adjusting for asbestos exposure and smoking, a beta-carotene level at the 75th rather than the 25th percentile was associated with FEV1 90 ml and FVC 82 ml above predicted values. For retinol, the FVC difference was 69 ml, and the FEV1 association was no longer statistically significant. Diet questionnaire answers did not predict lung function. The authors concluded that the vitamins had protective effects. They named the cross-sectional design as a limitation and said routine beta-carotene supplementation cannot be recommended.

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: Cross-sectional analysis of pre-randomization baseline data from the pilot phase of CARET, a randomized, placebo-controlled lung cancer chemoprevention trial
• Who was studied: 816 men aged 45 to 74 with extensive past occupational asbestos exposure, enrolled in the Seattle, Washington area between June 1985 and June 1988. Eighteen were excluded for missing data, leaving 798: 706 whose spirometry met American Thoracic Society criteria and 92 whose spirometry did not. 16% had never smoked, 62% were ex-smokers and 22% were current smokers. Women were excluded. Predicted lung function was based on the rest of the CARET asbestos-exposed population (the Efficacy cohort).
• Exposure: Past occupational asbestos exposure; no fiber type is named. Entry required either first exposure at least 15 years earlier plus chest X-ray findings of asbestosis or asbestos-related pleural disease, or at least 5 years in a high-risk trade: asbestos insulators, sheet-metal workers, plumbers/pipefitters, plaster board workers, boilermakers, shipyard electricians, ship scalers and ship fitters. The factors studied in relation to lung function were blood (serum) levels of beta-carotene and retinol.
• Main results:
  • Serum levels of both beta-carotene and retinol were inversely associated with the profusion of small, irregular opacities consistent with asbestosis on chest X-rays (p less than 0.05).
  • Beta-carotene, but not retinol, was lower in smokers. Current smokers had the lowest beta-carotene (geometric mean 111 ng/ml) and never smokers the highest (geometric mean 191 ng/ml).
  • Without adjustment, the difference between the 25th and 75th percentiles of beta-carotene (155 ng/ml) corresponded to 126 ml higher FEV1 and 118 ml higher FVC.
  • In all 798 participants, after adjusting for both asbestos exposure and smoking, raising beta-carotene from the 25th to the 75th percentile was associated with FEV1 90 ml higher and FVC 82 ml higher than predicted.
  • For retinol, raising the level from the 25th to the 75th percentile (211 ng/ml) was associated with FVC 69 ml higher in the model adjusting for both asbestos and smoking. The FEV1 association was no longer significant in that model.
  • Dietary intake of beta-carotene and retinol reported on the food frequency questionnaire did not predict lung function.
  • The interaction between pack-years smoked and beta-carotene level was not significant. In subgroups, the beta-carotene association was greatest in the small group of never smokers, less in current smokers and least in former smokers.
• The authors' conclusion: The authors concluded that serum beta-carotene and retinol had protective effects on lung function in men with occupational asbestos exposure and high rates of current or past smoking. They called the size of the effect moderate. Because increased lung cancer and cardiovascular mortality had been observed in current and former smokers taking 20 to 30 mg/day of beta-carotene, they stated that routine supplementation cannot be recommended.
• Limitations the authors state:
  • The cross-sectional design. The authors stated that whether higher vitamin intake actually causes better lung function would be better assessed in a longitudinal study with a control group.
  • Women were not included and few minority participants were recruited, so the results cannot be extended to these groups.
  • The results may not apply to people without asbestos exposure. The vitamins might act on asbestos-related scarring rather than on smoking-related airway obstruction.
  • A single blood measurement of beta-carotene or retinol may not be a sufficiently reliable indicator of vitamin intake.

Topics

Medical terms in this study, explained in our Lexicon: Lung Cancer, Spirometry, Chest X-Ray, FEV1, Confounding, Asbestos Exposure.

Related studies

• Risk factors for lung cancer and for intervention effects in CARET, the Beta-Carotene and Retinol Efficacy Trial — G.S. Omenn, G.E. Goodman, et al. (1996)
• No dose-dependent increase in fracture risk after long-term exposure to high doses of retinol or beta-carotene — G.L. Ambrosini, A.P. Bremner, et al. (2013)
• Vitamin A and cancer prevention II: comparison of the effects of retinol and beta-carotene — N.H. de Klerk, A.W. Musk, et al. (1998)
• CARET, the beta-carotene and retinol efficacy trial to prevent lung cancer in asbestos-exposed workers and in smokers — G.S. Omenn, G. Goodman, et al. (1991)
• Plasma retinol, carotene and vitamin E concentrations and lung function in a crocidolite-exposed cohort from Wittenoom, Western Australia: a cohort study — H.S. Alfonso, L. Fritschi, et al. (2005)
• Predictors of lung cancer among asbestos-exposed men in the {beta}-carotene and retinol efficacy trial — M.R. Cullen, M.J. Barnett, et al. (2005)

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