The potential role of antioxidant vitamins in preventing cardiovascular diseases and cancers

Our plain-English summary of The potential role of antioxidant vitamins in preventing cardiovascular diseases and cancers, by S. Hercberg, P. Galan, P. Preziosi, et al (Nutrition, 1998).

The study

• Authors: S. Hercberg, P. Galan, P. Preziosi, M.J. Alfarez, C. Vazquez
• Journal: Nutrition
• Published: 1998;14(6):513-20
• Type of article: Review
• Cited by: 74 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Cardiovascular diseases and cancers constitute major public health problems in all industrialized countries, where they are the main causes of premature mortality. There is a large body of evidence suggesting that free-radical production can directly or indirectly play a major role in cellular processes implicated in atherosclerosis and carcinogenesis. Here we present mechanistic data and results of epidemiologic studies on the relationship between antioxidant vitamin intake or biochemical status and the risk of cancer and cardiovascular diseases. Most epidemiologic data obtained on this topic were based on an observational approach, i.e., ecologic, case-control, or prospective studies. All these studies indicate that a high dietary intake or high blood concentrations of antioxidant vitamins are associated with a reduced risk of cardiovascular diseases and cancer at several common sites. Although the results of these studies are convergent, they merely suggest a relationship at the population and individual level but do not affirm a causality link. Only intervention studies (randomized trials), by specifically changing antioxidant vitamin intake, can provide conclusive answers. The apparent discrepancies between the results of four recently published trials may be explained by the type of population (general or high-risk subjects), the differing doses of supplementation (nutritional levels or higher), the number of antioxidants tested (one, two, or more), and the type of administration (alone or in balanced association). It thus appears that a low risk of pathologies may be related to multiple nutrients consumed at nutritional doses and in combination. Optimal effects may be expected with a combination of nutrients at levels similar to those found in a healthy diet. A single antioxidant vitamin given at high doses in subjects with high risk of pathologies (smokers, asbestos-exposed subjects) may not have substantial benefits and could even have negative consequences.

In plain English

This was a review article, not a new study. The authors summarized laboratory evidence, population studies and randomized trials on antioxidant vitamins (beta-carotene, vitamin C and vitamin E) and the risk of cancer and cardiovascular disease. Many earlier studies linked high intake or high blood levels of these vitamins with reduced risk of cardiovascular disease and cancer, but the authors stressed that such studies do not establish a causal link. Asbestos-exposed workers appeared as one high-risk group; the one trial described as enrolling them was the US CARET trial. It enrolled 18 314 heavy smokers or asbestos-exposed workers, giving 30 mg/d of beta-carotene plus 25 000 IU of retinol, or placebo. Lung cancer was significantly more frequent with the supplements than with placebo. A Finnish trial in male heavy smokers (ATBC) also found significantly more lung cancer with beta-carotene. The authors concluded that a single antioxidant vitamin given at high doses to high-risk subjects, such as smokers and asbestos-exposed subjects, may not have substantial benefits and could even have negative consequences. They hypothesized that a balanced combination of antioxidants may provide maximal efficacy with maximal safety.

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 mechanistic (laboratory and animal) evidence, observational epidemiologic studies and randomized intervention trials on antioxidant vitamins
• Who was studied: No new subjects. The authors reviewed previously published mechanistic and epidemiologic studies, including observational studies and randomized trials. One of these trials (CARET, US) enrolled 18 314 heavy smokers or asbestos-exposed workers.
• Exposure: Antioxidant vitamins (beta-carotene, vitamin C, vitamin E) from diet or supplements. Asbestos-exposed workers appear as one of the high-risk groups in the authors' discussion of high-dose supplementation. CARET is the trial described as enrolling them. No fiber types, jobs or asbestos doses are given.
• Main results:
  • The authors reported that earlier case-control and prospective studies (not this review's own data) showed high dietary intake or high blood levels of antioxidant vitamins associated with reduced risk of cardiovascular diseases and cancer at several sites.
  • The CARET trial enrolled heavy smokers or asbestos-exposed workers. Participants received 30 mg/d of beta-carotene and 25 000 IU of retinol, or placebo, for an average of 4 years.
  • In the CARET trial, lung cancer was significantly more frequent in the group given beta-carotene with vitamin A than in the placebo group.
  • In the Finnish ATBC trial of 29 133 male heavy smokers aged 50 to 59, beta-carotene supplements were associated with a significant increase in lung cancer incidence.
  • The authors reported that the beta-carotene supplements raised initial blood beta-carotene levels 18-fold in ATBC and 12-fold in CARET. They stated these levels were much higher than those linked to lower risk in observational studies.
  • In the Linxian trial in a general Chinese population of 29 584 subjects (mostly nonsmokers), daily beta-carotene, vitamin E and selenium over more than 5 years significantly reduced overall mortality by 9%, all-cancer mortality by 13% and gastric cancer mortality by 21%.
  • In the US Physicians' Health Study of 22 071 male physicians, beta-carotene supplementation showed no positive or negative effects after 12 years of follow-up.
• The authors' conclusion: The authors concluded that a single antioxidant vitamin given at high doses to high-risk subjects (smokers, asbestos-exposed subjects) may not have substantial benefits and could even have negative consequences. They hypothesized that a balanced combination of antioxidants, rather than a single nutrient, may provide maximal efficacy with maximal safety.
• Limitations the authors state:
  • The authors stated that the observational studies they reviewed suggest a relationship but do not establish that the vitamins cause the lower risk.
  • The authors stated that case-control studies cannot determine whether the measured intake or blood levels existed before the disease or resulted from it.

Topics

Medical terms in this study, explained in our Lexicon: Carcinogenesis.

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