Effects of Beta-carotene Supplementation Debated

SEATTLE, Wash.--Incidence of lung cancer and all-cause mortality remained elevated in females and former smokers who took high daily doses of beta-carotene and retinyl palmitate during a large-scale, randomized trial, according to a follow-up study published in the Dec. 1 issue of the Journal of the National Cancer Institute (JNCI) (96, 23:1743-1750, 2004) (http://jncicancerspectrum.oupjournals.org).

According to the authors of the six-year follow-up study (Gary E. Goodman et al), the incidence of lung cancer remained elevated by 12 percent and all-cause mortality by 8 percent in 18,314 subjects who had received 30 mg/d beta-carotene and 25,000 IU/d retinyl palmitate as part of The Beta-Carotene and Retinol Efficacy Trial (CARET), with these risks at their highest during the first three years following the original study. The excess risk of lung cancer was linked primarily to females and former smokers. An elevated risk of cardiovascular disease was also observed among of CARET participants, although the risk waned rapidly after intervention was stopped.CARET was halted prematurely in 1996 after researchers linked its participants intake of beta-carotene to adverse effects including increased risk of lung cancer, death and cardiovascular disease.

The results of the CARET trial paralleled those of the Alpha-Tocopherol Beta-Carotene (ATBC) Trial, a similar, large-scale, randomized trial that tested the effects of 50 mg/d alpha-tocopherol and/or 20 mg/d beta-carotene on more than 29,000 male smokers. Like CARET, the ATBC trial was also stopped after adverse trends including lung cancer were observed among its test subjects.

However, according to an editorial published in the same issue of JNCI (96, 23:1743-1750, 2004), the adverse effects linked to beta-carotene in the CARET and ATBC trials might be incorrect since similar clinical trials have not produced similar effects. One such study, the Physicians Health Study (PHS), a large prevention trial of beta-carotene, did not show a high incidence of lung cancer or all-cause mortality among test subjects. However, PHS test subjects were not principally composed of current or former smokers (11 percent of participants were current smokers; 30 percent were former smokers) and were not administered as much beta-carotene as in CARET or ATBC (50 mg given every other day). Two smaller studies in which beta-carotene also did not appear to produce adverse cardiovascular, cancer and mortality endpoints included the Womens Health Study, which administered 50 mg beta-carotene to test subjects every other day for 2.1 years (13 percent of study participants were smokers), and the Skin Cancer Prevention Study, which tested the effects of 50 mg/d beta-carotene among 1,805 patients recently diagnosed with a nonmelanoma skin cancer.

The authors of the JNCI editorial also criticized the Goodman study for linking the adverse effects of beta-carotene exclusively to females and former smokers, as males showed excess risks of both lung cancer and all-cause mortality during the intervention phase of CARET, and the ATBC trial was conducted entirely on male participants. In addition, the authors of the editorial criticized the decision by Goodman et al to link excess cardiovascular disease mortality to former smokers and women because of the relatively low occurrence of cardiovascular disease mortality in the CARET trial and the increased incidence of this endpoint among male smokers during both the intervention and follow-up phases of the ATBC trial.