Protective dietary factors and lung cancer

Our plain-English summary of Protective dietary factors and lung cancer, by E.T. Fontham (International Journal of Epidemiology, 1990).

The study

• Author: E.T. Fontham
• Journal: International Journal of Epidemiology
• Published: 1990;19 Suppl 1:S32-42
• Type of article: Review
• Cited by: 92 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Since the first report of a protective effect of dietary vitamin A on lung cancer risk was issued in 1975, a succession of retrospective (case-control) and prospective (cohort) epidemiological studies have examined the association. Food frequency questionnaires have been used to assess dietary intake of food groups and to generate indices of specific dietary components, in particular retinol and carotene. Serum levels of retinol, carotenoids, and other micronutrients have been determined as well, and related to risk of lung cancer. The dietary studies have been notably consistent, finding an approximate 50% reduction in risk associated with high compared to low consumption of carotene-containing fruits and vegetables. Unresolved issues include gender differences, histological specificity and the interaction with cigarette smoking as well as the role of other possible protective factors found in these foods--indoles, vitamin C, trace minerals. Most studies in which serum beta-carotene was assayed in prospectively collected blood samples have found lower levels of beta-carotene in people who subsequently developed lung cancer. Unlike carotene, blood retinol levels do not reflect dietary intake under normal conditions and, as might be expected, have failed to show a consistent relation with risk of lung cancer. Although epidemiological studies have not strongly supported the role of preformed retinol as a protective agent, animal studies have provided convincing evidence that retinol and synthetic retinoids are protective against epithelial tumours including those of the lung. A number of on-going clinical trials are testing the efficacy of retinol, beta-carotene, synthetic retinoids and alpha-tocopherol for preventing cancer of the lung, especially in high risk groups such as heavy smokers, miners and asbestos workers. It is hoped that these trials will help explain the nature of the observed protective effect of fruit and vegetables.

In plain English

This single-author review covered case-control and cohort studies from the 1975 first report onward. It examined diet and lung cancer, mainly fruit, vegetables, vitamin A, retinol and carotene. The author reported notably consistent dietary findings: an approximate 50% reduction in risk with high versus low intake of carotene-containing fruits and vegetables. Most studies of pre-diagnosis blood found lower beta-carotene in people later developing lung cancer. Epidemiological studies did not strongly support preformed retinol as protective, though the author called animal evidence for retinol and synthetic retinoids against epithelial tumours, including lung tumours, convincing. Findings were more convincing for men than women, which the author said likely reflected more and larger studies of men; protective effects appeared mainly in smokers, but few had never smoked, so effects in non-smokers remained undetermined. The author cautioned that inadequate smoking adjustment could give false estimates and that other food substances might explain the effect. The author concluded that randomized prevention trials are needed and preventing and stopping smoking remain the most viable means of reducing risk. The review presented no asbestos data.

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: Narrative review of published epidemiological studies (case-control, cohort and blood-level studies) on diet and lung cancer
• Who was studied: Published studies from 1975 to 1989 in several countries, including 18 case-control studies and four cohort studies of diet, plus a series of serum studies; populations included men and women in Norway, the US, Japan, Hong Kong, Singapore, Italy, England and Australia
• Exposure: Dietary intake of fruit, vegetables, vitamin A, retinol and carotene, assessed mostly by food frequency questionnaires, and blood levels of retinol, carotenoids, vitamin E and selenium; also dietary vitamin C. Asbestos was not an exposure studied; asbestos workers were mentioned only as a high-risk group in ongoing trials.
• Main results:
  • Across the reviewed dietary studies, the author described an approximate 50% reduction in lung cancer risk with high compared to low consumption of carotene-containing fruits and vegetables
  • In the studies of fruit and vegetables as food groups, high intake was associated with relative risks ranging from 0.3 to 0.8; only one study failed to find a protective effect
  • Most studies of blood samples collected before diagnosis found lower beta-carotene levels in people who later developed lung cancer
  • Human epidemiological studies did not strongly support preformed retinol as protective, and the collected serum data did not support a relationship between serum retinol and lung cancer risk
  • The author stated that animal studies had provided convincing evidence that retinol and synthetic retinoids are protective against epithelial tumours, including those of the lung
  • Findings on plant-derived dietary protection were more convincing for males than females, which the author thought likely reflected more studies and larger samples of males
  • Most studies found protective effects mainly in smokers; most had very few people who had never smoked, so effects in non-smokers remained to be determined
  • Most studies reported no effect of dietary vitamin C, though some recent studies found reduced risk, with the effect more apparent in males
• The authors' conclusion: The author concluded that the effectiveness of dietary constituents in preventing cancer must be tested in double-blind randomized chemoprevention trials, and that preventing and stopping cigarette smoking remain the most viable means of reducing lung cancer risk
• Limitations the authors state:
  • Adjustment for smoking in the reviewed studies was usually crude, so lower fruit and vegetable intake among heavier smokers could produce false estimates of risk attributed to diet
  • Retrospective case-control studies are subject to differential recall bias in reporting diet
  • Beta-carotene, whether measured in diet or blood, may only be a marker for other substances in fruit and vegetables
  • Most studies had very few people who had never smoked, so effects in non-smokers remain to be determined
  • Blood samples collected after diagnosis cannot separate a pre-existing cause from an effect of the cancer itself

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: Lung Cancer, Clinical Trial.

Related studies

• Fruit, vegetable, vitamin A intakes, and prostate cancer risk — G.L. Ambrosini, N.H. de Klerk, et al. (2008)
• The role of carotenoids in human health — E.J. Johnson (2002)
• Dietary intake and the risk of malignant mesothelioma — J.E. Muscat, M. Huncharek (1996)
• Increased urinary 8-isoprostaglandin F(2)alpha is associated with lower plasma selenium levels and lower vegetable and fruit intake in an asbestos-exposed cohort at risk for lung cancer — E.B. Gottschall, P. Wolfe, et al. (2004)
• The role of intervention studies in ascertaining the contribution of dietary factors in lung cancer. The Seattle chemoprevention trial of retinoids in asbestos-exposed workers — G.S. Omenn, G.E. Goodman, et al. (1988)
• Association between diet and lung cancer location — B.W. Lee, J.C. Wain, et al. (1998)

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