The role of carotenoids in human health

Our plain-English summary of The role of carotenoids in human health, by E.J. Johnson (Nutrition in Clinical Care, 2002).

The study

• Author: E.J. Johnson
• Journal: Nutrition in Clinical Care
• Published: 2002;5(2):56-65
• Type of article: Review
• Cited by: 240 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Dietary carotenoids are thought to provide health benefits in decreasing the risk of disease, particularly certain cancers and eye disease. The carotenoids that have been most studied in this regard are beta-carotene, lycopene, lutein, and zeaxanthin. In part, the beneficial effects of carotenoids are thought to be due to their role as antioxidants. beta-Carotene may have added benefits due its ability to be converted to vitamin A. Furthermore, lutein and zeaxanthin may be protective in eye disease because they absorb damaging blue light that enters the eye. Food sources of these compounds include a variety of fruits and vegetables, although the primary sources of lycopene are tomato and tomato products. Additionally, egg yolk is a highly bioavailable source of lutein and zeaxanthin. These carotenoids are available in supplement form. However, intervention trials with large doses of beta-carotene found an adverse effect on the incidence of lung cancer in smokers and workers exposed to asbestos. Until the efficacy and safety of taking supplements containing these nutrients can be determined, current dietary recommendations of diets high in fruits and vegetables are advised.

In plain English

This article was a review, not an original study. The author summarized published research on carotenoids, the plant pigments in fruits and vegetables. It focused on beta-carotene, lycopene, lutein and zeaxanthin and their possible role in lowering the risk of certain cancers and eye disease. Asbestos appeared only in the discussion of supplement trials. The author reported that large randomized trials had tested high doses of beta-carotene (20 to 30 mg per day) to prevent cancer. The author reported that 2 trials gave possible evidence of harm among high-risk people such as smokers and asbestos workers: a possible adverse effect on the incidence of lung cancer. The author separately reported no effect, neither beneficial nor harmful, in a generally well-nourished population. The review also described other researchers' findings, including that 11 of 15 prospective studies showed an inverse relation between beta-carotene and lung cancer risk. The author noted that epidemiological studies cannot show cause and that results were not entirely consistent. The author concluded that recommending supplements must come with a cautionary note because of those trials.

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 epidemiologic studies and intervention trials on carotenoids and disease; no new data
• Who was studied: No study population of its own; the author reviewed previously published human studies (case-control, cohort, ecologic studies and randomized trials) of carotenoids and cancer or eye disease
• Exposure: Dietary and supplemental carotenoids, mainly beta-carotene, lycopene, lutein and zeaxanthin. Asbestos is mentioned only as a characteristic of a high-risk group in beta-carotene supplement trials; the article gives no asbestos exposure data.
• Main results:
  • As reported by the author from earlier trials: high-dose beta-carotene (20 to 30 mg per day) trials tested cancer prevention. Results from 2 trials provided possible evidence of harm in relation to cancer among high-risk individuals such as smokers and asbestos workers. The conclusions describe this as a possible adverse effect on the incidence of lung cancer in smokers and workers exposed to asbestos.
  • As reported by the author: no effect of beta-carotene supplements (neither beneficial nor detrimental) was found in a generally well-nourished population.
  • As reported by the author from earlier studies: 11 of 15 prospective epidemiologic studies showed a significant inverse relation between beta-carotene intake and/or plasma level and lung cancer risk.
  • As reported by the author: in the Linxian (Chinese) Cancer Prevention Study, supplementation with beta-carotene, vitamin E and selenium led to a significant reduction in total mortality (9%), in cancer mortality (13%) and in stomach cancer mortality (21%). The author suggested this may reflect correction of a nutrient deficiency.
  • As reported by the author from an earlier case-control study: subjects in the highest quintile of lutein/zeaxanthin intake had a 57% lower risk of advanced age-related macular degeneration than those in the lowest quintile.
• The authors' conclusion: The author concluded that advocating nutrient supplements must be done with caution, because trials suggested beta-carotene supplementation may have an adverse effect on lung cancer incidence in smokers and workers exposed to asbestos. Until the efficacy and safety of supplements can be determined, the author advised following current dietary recommendations of diets high in fruits and vegetables.
• Limitations the authors state:
  • The author stated that epidemiological studies cannot provide evidence of a causal relationship.
  • The author stated that results of the epidemiologic studies have not been entirely consistent.
  • The author stated that research to date has not sufficiently evaluated the effectiveness versus safety of nutrient supplements.

Topics

Medical terms in this study, explained in our Lexicon: Lung Cancer.

Related studies

• Carotenoid actions and their relation to health and disease — N.I. Krinsky, E.J. Johnson (2005)
• Beta-carotene and other carotenoids as antioxidants — S.A. Paiva, R.M. Russell (1999)
• Protective dietary factors and lung cancer — E.T. Fontham (1990)
• Fruit, vegetable, vitamin A intakes, and prostate cancer risk — G.L. Ambrosini, N.H. de Klerk, et al. (2008)
• 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)
• Changes in cholesterol and triglyceride concentrations in the Vanguard population of the Carotene and Retinol Efficacy Trial (CARET) — B. Cartmel, J. Dziura, et al. (2005)

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