Dietary vitamin A and prevalence of bronchial metaplasia in asbestos-exposed workers

Our plain-English summary of Dietary vitamin A and prevalence of bronchial metaplasia in asbestos-exposed workers, by S.T. Mayne, C.A. Redlich, M.R. Cullen (The American Journal of Clinical Nutrition, 1998).

The study

• Authors: S.T. Mayne, C.A. Redlich, M.R. Cullen
• Journal: The American Journal of Clinical Nutrition
• Published: 1998;68(3):630-5
• Cited by: 3 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The purpose of this investigation was to examine the association between dietary intake of vitamin A in the form of retinol and provitamin A carotenoids and the prevalence of bronchial squamous metaplasia in a sample of asbestos workers from an industrial clinic. Bronchial biopsies were obtained from 49 asbestos workers. Pulmonary function testing was done and in-person interviews were conducted to estimate dietary intake of retinol and provitamin A carotenoids, tobacco exposure, and asbestos exposure. Results indicated that workers with metaplasia reported consuming a significantly lower intake of total vitamin A [2000 retinol equivalents (RE)/d] than did subjects without metaplasia (2710 RE/d, P = 0.02). Logistic regression analyses showed that higher intakes of retinol [odds ratio (OR): 0.31; 95% CI: 0.04, 2.44], provitamin A carotenoids (OR: 0.31; 95% CI: 0.03, 2.84), and total vitamin A (OR: 0.29; 95% CI: 0.03, 2.49) were associated with a nonsignificant reduction in the OR for metaplasia (highest quartile compared with lowest quartile, adjusted ORs). Current smoking (OR: 5.25; 95% CI: 0.50, 55.1) and former smoking (OR: 2.95; 95% CI: 0.31, 28.1) were associated with a nonsignificant increase in the OR for bronchial metaplasia compared with never smoking. Greater airway obstruction [decreased forced expiratory volume in 1 s (FEV1)/forced vital capacity (FVC)] was associated with an increased OR for metaplasia (OR: 2.86; 95% CI: 1.09, 7.69). These results suggest that a higher (ie, above the median) intake of vitamin A from foods decreases the risk of bronchial metaplasia in workers occupationally exposed to asbestos.

In plain English

This cross-sectional study asked whether vitamin A from food was related to bronchial squamous metaplasia, an abnormal change in the airway lining, in 49 men with past occupational asbestos exposure. The men had airway biopsies, lung function tests and a dietary interview. Asbestos dose was estimated in insulator-years; fiber types were not named. Fifteen men had metaplasia. They reported eating less total vitamin A than the others (2000 versus 2710 retinol equivalents per day, P = 0.02). Comparing the highest with the lowest quarter of intake, adjusted odds ratios for metaplasia were below 1 (total vitamin A 0.29, 95% CI 0.03 to 2.49), but none was statistically significant. A 13.3% decrease in FEV1/FVC (the interquartile range), meaning greater airway obstruction, was significantly linked to metaplasia (adjusted odds ratio 2.79, 95% CI 1.03 to 7.58). Smoking and higher asbestos dose had raised but not significant odds ratios. The authors concluded the data showed no evidence that more dietary vitamin A harms asbestos workers, but evidence of a protective effect. They named the small sample size as the major limitation.

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 study comparing workers with and without bronchial squamous metaplasia found on bronchoscopic biopsy, using logistic regression
• Who was studied: 49 men with a history of occupational asbestos exposure, mean age 60. They were recruited from an occupational medicine clinic among workers whose abnormal chest radiographs indicated significant prior asbestos exposure, and were studied at the Yale General Clinical Research Center, New Haven, CT. Of 56 recruited, 4 could not be bronchoscoped and 3 did not complete the dietary interview. 27 were former smokers, 14 current smokers and 8 never smokers. Study dates were not given.
• Exposure: Occupational asbestos exposure (fiber types not named), estimated as cumulative dose in insulator-years: mean 14, range 3 to 34. Insulators and highly dusty manufacturing workers scored 1 per year of employment; other trades scored 0.1 to 0.5. Dietary vitamin A (retinol, provitamin A carotenoids and total vitamin A) was estimated from an 86-item food-frequency questionnaire. Smoking history was also recorded.
• Main results:
  • 15 of the 49 men had bronchial squamous metaplasia
  • Men with metaplasia reported a significantly lower total vitamin A intake (2000 retinol equivalents per day) than men without metaplasia (2710 retinol equivalents per day), P = 0.02
  • Highest versus lowest quartile of intake, adjusted odds ratios for metaplasia: total vitamin A 0.29 (95% CI 0.03, 2.49), retinol 0.31 (95% CI 0.04, 2.44), provitamin A carotenoids 0.31 (95% CI 0.03, 2.84). The authors called these reductions nonsignificant, and the tests for linear trend were not significant. The adjustment covered smoking status, age, pack-years, asbestos dose and FEV1/FVC.
  • Greater airway obstruction (a 13.3% decrease in FEV1/FVC, the interquartile range) was associated with higher odds of metaplasia: unadjusted OR 2.86 (95% CI 1.09, 7.69); adjusted for pack-years and other covariates, OR 2.79 (95% CI 1.03, 7.58)
  • Compared with never smokers, current smokers had an OR for metaplasia of 5.25 (95% CI 0.50, 55.1) and former smokers 2.95 (95% CI 0.31, 28.1). These increases were not statistically significant.
  • Estimated cumulative asbestos dose was associated with a 46% increase in the OR for metaplasia (OR 1.46, 95% CI 0.68, 3.15) for a difference of 10.1 insulator-years. This was not statistically significant.
• The authors' conclusion: The authors concluded that asbestos workers with metaplasia consumed significantly less total vitamin A, and that the apparent protective effect did not appear to be due to confounding. In their view, the data provide no evidence that higher dietary vitamin A intake is harmful to asbestos workers, and instead show evidence of protective effects of vitamin A in foods against lung cancer risk in this population.
• Limitations the authors state:
  • Small sample size, because bronchial biopsies are invasive, carry risk and are expensive
  • Food-frequency questionnaires may not accurately measure actual nutrient intake
  • Vitamin A intake was likely overestimated, which may limit comparisons with other populations
  • Results could not be adjusted for energy intake, because the questionnaire did not capture all major sources of energy

Topics

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

Related studies

• Association between acute inflammatory cells in lavage fluid and bronchial metaplasia — W.W. Merrill, M.R. Cullen, et al. (1992)
• Peribronchiolar metaplasia: a common histologic lesion in diffuse lung disease and a rare cause of interstitial lung disease: clinicopathologic features of 15 cases — J. Fukuoka, T.J. Franks, et al. (2005)
• Estimated intake of vitamin D and its interaction with vitamin A on lung cancer risk among smokers — T.Y. Cheng, G.E. Goodman, et al. (2014)
• The relationship between large airway inflammation and airway metaplasia — W.W. Merrill, D. Carter, et al. (1991)
• The relationship between large airway and alveolar space inflammation and airway metaplasia — W.W. Merrill, D. Carter, et al. (1992)
• 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)

Browse more research in The American Journal of Clinical Nutrition, or return to medical research.