Carotenoid actions and their relation to health and disease

Our plain-English summary of Carotenoid actions and their relation to health and disease, by N.I. Krinsky, E.J. Johnson (Molecular Aspects of Medicine, 2005).

The study

• Authors: N.I. Krinsky, E.J. Johnson
• Journal: Molecular Aspects of Medicine
• Published: 2005;26(6):459-516
• Type of article: Review
• Cited by: 669 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Based on extensive epidemiological observation, fruits and vegetables that are a rich source of carotenoids are thought to provide health benefits by decreasing the risk of various diseases, particularly certain cancers and eye diseases. 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. Additionally, 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 2005 article was a review, not a new study. The authors summarized published research on carotenoids, which are pigments found in fruits and vegetables. They focused on beta-carotene, lycopene, lutein and zeaxanthin and covered food sources, absorption, laboratory work on antioxidant and pro-oxidant effects, effects on cells, and human studies of cancer, heart disease and eye disease. Asbestos came up only in the discussion of supplement trials. The authors reported that 11 of 15 prospective studies they listed found a significant inverse relation between beta-carotene intake or blood levels and lung cancer risk. They wrote that two large trials of high-dose beta-carotene (20 to 30 mg per day) gave possible evidence of harm in relation to cancer among high-risk people such as smokers and asbestos workers. They also reported that in the CARET trial, beta-carotene combined with vitamin A was followed by a non-significant 26% increase in cardiovascular deaths among smokers, former smokers and asbestos-exposed people. The authors concluded that supplements should be advocated only with caution, and that diets high in fruits and vegetables are advised.

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 laboratory, animal, observational and intervention studies on carotenoids
• Who was studied: No study population of its own. The review covered published research, mainly on four carotenoids: beta-carotene, lycopene, lutein and zeaxanthin.
• Exposure: Carotenoids from foods and supplements. The intervention trials discussed used high doses of beta-carotene (20 to 30 mg per day). Asbestos workers were mentioned only as one of the high-risk groups in those trials. No fiber type was named.
• Main results:
  • Observational studies reviewed: 11 of 15 prospective studies showed a significant inverse relation between beta-carotene intake and/or plasma level and lung cancer risk.
  • Intervention trials reviewed: results from two trials gave possible evidence of harm from beta-carotene supplements in relation to cancer among high-risk individuals such as smokers and asbestos workers. The authors cited the Alpha-Tocopherol Beta Carotene study (1994) and Omenn et al. (1996).
  • The authors stated that trials have suggested beta-carotene supplementation may have an adverse effect on the incidence of lung cancer in smokers and workers exposed to asbestos.
  • CARET trial as reported in the review: beta-carotene (30 mg/d) combined with vitamin A (25,000 IU/d) was associated with a non-significant 26% increase in mortality from cardiovascular disease in a group of smokers, former smokers and asbestos-exposed individuals.
  • Other trials reviewed: no effect was found in a generally well-nourished population. In the Linxian (China) trial, beta-carotene, vitamin E and selenium together led to a significant reduction in total mortality (9%) and in cancer mortality (13%). The authors suggested this may reflect correction of a nutrient deficiency.
• The authors' conclusion: The authors concluded that supplement use must be advocated with caution because of the trials suggesting harm in smokers and asbestos-exposed workers. They called for further trials, and advised diets high in fruits and vegetables until the efficacy and safety of supplements are determined.
• Limitations the authors state:
  • The authors noted that epidemiological studies cannot provide evidence of a causal relationship.
  • The authors stated that research to date has not sufficiently evaluated the effectiveness versus the safety of nutrient supplements.

Topics

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

Related studies

• The role of carotenoids in human health — E.J. Johnson (2002)
• Beta-carotene and other carotenoids as antioxidants — S.A. Paiva, R.M. Russell (1999)
• Chemoprevention of cancer: lessons to be learned from beta-carotene trials — H. Vainio (2000)
• Effects of a combination of beta carotene and vitamin A on lung cancer and cardiovascular disease — G.S. Omenn, G.E. Goodman, et al. (1996)
• 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)
• Association between diet and lung cancer location — B.W. Lee, J.C. Wain, et al. (1998)

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