Beta carotene fails to prevent cancer in two major studies; CARET intervention stopped

Our plain-English summary of Beta carotene fails to prevent cancer in two major studies; CARET intervention stopped, by K. Smigel (Journal of the National Cancer Institute, 1996).

The study

• Author: K. Smigel
• Journal: Journal of the National Cancer Institute
• Published: 1996;88(3-4):145
• Type of article: News
• Cited by: 23 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Summary of the article

This news report, published in February 1996, described two large trials of beta carotene supplements whose results were announced at a press conference before journal publication. In the Physicians' Health Study, led by Charles Hennekens, 22,071 male doctors took 50 mg of beta carotene every other day for more than 12 years. The supplement did not reduce the number of cancers, heart attacks, or deaths of any type. The Beta Carotene and Retinol Efficacy Trial (CARET) enrolled 14,254 current and former smokers with a long smoking history and 4,060 asbestos-exposed individuals, most of whom also smoked. It was stopped 21 months early because participants taking 30 mg of beta carotene plus 25,000 international units of vitamin A had 28% more lung cancers than those taking placebo. After an average of 4 years they also had 17% higher total mortality and 26% higher cardiovascular mortality. Participants were to be followed for at least 5 more years. Investigator Gilbert Omenn said former smokers seemed to respond more favorably, but the data were too limited to draw conclusions. The report noted that a 1994 trial of 29,133 male smokers had found an 18% increase in lung cancers and an 8% increase in deaths with 20 mg of beta carotene daily. National Cancer Institute Director Richard Klausner said the studies showed that a healthful diet and lifestyle cannot be replaced with simple pills.

PubMed has no abstract for this study, and the article doesn't print one. We wrote this summary from the full article with the help of AI. It is not the authors' wording.

In plain English

This news article described results of two large trials released before publication. The Physicians' Health Study gave beta carotene for more than 12 years to 22,071 male doctors. In men taking 50 mg every other day, it did not decrease the number of cancers, heart attacks, or any type of death. The Beta Carotene and Retinol Efficacy Trial (CARET) enrolled 14,254 current and former smokers with a long history of smoking and 4,060 asbestos-exposed individuals, most of whom also smoked. The investigators stopped the intervention 21 months early because 28% more participants taking 30 mg beta carotene plus 25,000 international units of vitamin A got lung cancer than those on placebo. After an average of 4 years, vitamin-takers also had 17% higher total and 26% higher cardiovascular mortality. No separate results were given for the asbestos-exposed participants. CARET's Gilbert Omenn was quoted as saying there was no explanation for the possible adverse effects and that there can be little enthusiasm about the efficacy or safety of supplemental beta carotene or vitamin A for reducing population burdens of cancer or heart disease.

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: News article reporting on two large trials (the Physicians' Health Study and CARET) whose results were released before publication; not original research by the author
• Who was studied: Physicians' Health Study: 22,071 male doctors. CARET: 14,254 current and former smokers with a long history of smoking and 4,060 asbestos-exposed individuals, most of whom also smoked
• Exposure: CARET: a combination of 30 mg of beta carotene and 25,000 international units of vitamin A, compared with placebo. Physicians' Health Study: beta carotene supplements given for more than 12 years, with men taking a 50 mg dose every other day. The asbestos exposure of the CARET subgroup is not described further.
• Main results:
  • In CARET, the intervention was stopped 21 months early because 28% more participants taking beta carotene plus vitamin A got lung cancer than those on placebo
  • CARET vitamin-takers had 17% higher total mortality and 26% higher cardiovascular mortality after an average of 4 years in the study
  • In the Physicians' Health Study, the beta carotene supplement did not decrease the number of cancers, heart attacks, or any type of death in men taking a 50 mg dose every other day
  • In CARET, former smokers (about 34% of participants at the start) who took beta carotene and vitamin A seemed to respond more favorably, but the data were too limited to draw conclusions
• The authors' conclusion: CARET investigator Gilbert Omenn was quoted as saying the investigators had no explanation for the possible adverse effects, and that there can be little enthusiasm about the efficacy or safety of supplemental beta carotene or vitamin A for reducing population burdens of cancer or heart disease
• Limitations the authors state:
  • Data on former smokers were too limited to draw any conclusions

Topics

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

Related studies

• CARET, the beta-carotene and retinol efficacy trial to prevent lung cancer in asbestos-exposed workers and in smokers — G.S. Omenn, G. Goodman, et al. (1991)
• Recruitment for the beta-carotene and retinol efficacy trial (CARET) to prevent lung cancer in smokers and asbestos-exposed workers — G.S. Omenn, G. Goodman, et al. (1992)
• Risk factors for lung cancer and for intervention effects in CARET, the Beta-Carotene and Retinol Efficacy Trial — G.S. Omenn, G.E. Goodman, et al. (1996)
• Research cost analyses to aid in decision making in the conduct of a large prevention trial, CARET. Carotene and Retinol Efficacy Trial — M.D. Thornquist, N. Urban, et al. (1993)
• beta-Carotene fails to act as a tumor promoter, induces RAR expression, and prevents carcinoma formation in a two-stage model of skin carcinogenesis in male Sencar mice — R.M. Ponnamperuma, Y. Shimizu, et al. (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)

Browse more research in Journal of the National Cancer Institute, or return to medical research.