A global clinical view on vitamin A and carotenoids

Our plain-English summary of A global clinical view on vitamin A and carotenoids, by A. Sommer, K.S. Vyas (The American Journal of Clinical Nutrition, 2012).

The study

• Authors: A. Sommer, K.S. Vyas
• Journal: The American Journal of Clinical Nutrition
• Published: 2012;96(5):1204S-6S
• Type of article: Review
• Cited by: 138 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The clinical importance of vitamin A as an essential nutrient has become increasingly clear. Adequate vitamin A is required for normal organogenesis, immune competence, tissue differentiation, and the visual cycle. Deficiency, which is widespread throughout the developing world, is responsible for a million or more instances of unnecessary death and blindness each year. β-Carotene is an important, but insufficient, source of vitamin A among poor populations, which accounts for the widespread nature of vitamin A deficiency. It has only recently become apparent that the bioconversion of traditional dietary sources of β-carotene to vitamin A is much less efficient than previously supposed. The other major carotenoids, particularly lycopene, lutein, and zeaxanthin, have been found to have important biological properties, including antioxidant and photoprotective activity, and high intake has been linked in observational studies with reduced risk of a number of chronic diseases. But, to date, no clinical trials have proven the clinical value of ingested carotenoids individually or in combination, in either physiologic or pharmacologic doses, with the excepton of the provitamin A activity of carotene. Indeed, several trials have suggested an increased risk of lung cancer among high-risk individuals (smokers and asbestos workers) who were given high doses of β-carotene alone or in combination with other antioxidants. Much more evidence is needed before commonly encountered claims of the value of ingesting high doses of non-provitamin A carotenoids are validated.

In plain English

This article was a narrative review, presented at a 2011 conference on carotenoid research. The authors discussed published evidence on vitamin A and carotenoids and did not report new data. Carotenoids are pigments found in colored fruit and vegetables. The ones discussed were carotenes (which the body can convert to vitamin A), lycopene, lutein and zeaxanthin. The authors described research showing that the body gets considerably less use (one-half to one-fourth) from beta-carotene in traditional foods than was previously assumed. They noted that some observational studies linked high carotenoid intake with lower risk of chronic diseases, while other studies did not support this. Asbestos appeared only in their description of earlier trials by other researchers. In 2 randomized trials that enrolled people at high risk of lung cancer (smokers and/or asbestos workers), the active agents, including beta-carotene, appeared to increase the risk of developing lung cancer. The authors concluded that, until definitive clinical evidence is available, the importance and roles of carotenoids remain uncertain.

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 / commentary presented at a conference; no original data
• Who was studied: No study population of its own; the authors discussed published research on vitamin A deficiency, mainly in developing countries, and on carotenoids
• Exposure: Vitamin A and dietary or supplemental carotenoids (carotenes, lycopene, lutein, zeaxanthin). Asbestos workers appear only as participants in cited beta-carotene trials by other researchers.
• Main results:
  • From the literature reviewed (not this article's own data): the bioavailability of beta-carotene from traditional foods was one-half to one-fourth lower than previously assumed
  • From the literature reviewed: some analyses and observational studies did not support the reported links between high carotenoid intake and reduced chronic disease risk
  • From the literature reviewed: large randomized trials of beta-carotene (with or without alpha-tocopherol or retinol) did not find a consistent reduction in cancers, cancer deaths or cardiovascular disease
  • From the literature reviewed: in 2 trials enrolling people at high risk of lung cancer (smokers and/or asbestos workers), the active agents appeared to increase the risk of developing lung cancer
• The authors' conclusion: The authors concluded that, until definitive clinical evidence becomes available, humans are known to accumulate a variety of carotenoids but the importance and roles of these carotenoids remain uncertain.

Topics

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

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