Beta carotene supplementation not strongly linked to reduced cancer, CVD deaths -- JAMA.

SUPPLEMENTAL BETA CAROTENE NOT LINKED TO REDUCED MORTALITY from major diseases and, specifically, from cardiovascular disease and cancer, Robert Greenberg, MD, et al. Dartmouth Medical School/Norris Cotton Cancer Center, found in a study published in the Journal of the American Medical Association March 6. The study was designed to examine the relationship between beta carotene plasma concentration and beta carotene supplementation and risk of death from major disease causes.

Although the researchers observed "no support for a strong effect of supplemental beta carotene in reducing mortality from cardiovascular disease or other causes," the study reports that high concentrations of beta carotene in the blood prior to supplementation were associated with a reduced mortality rate.

Greenberg et al. stated that "persons whose initial plasma beta carotene concentrations were in the highest quartile...had a lower risk of death from all causes...compared with persons with initial concentrations in the lowest quartile." Overall, the study notes, mortality was 40% lower for those with initial beta carotene plasma concentrations above the median.

For subjects randomly assigned to beta carotene supplementation, however, "there was no evidence of lower mortality following supplementation," the study states. Despite the fact that their average plasma concentrations increased 10-fold during the study period -- "well above the highest quartiles of unsupplemented concentrations," the study points out -- risk of death from all causes for the supplemented subjects remained "about equal to that of patients assigned to placebo," researchers reported.

The multi-center, double-blind clinical trial involved 1,188 men and 532 women with a mean age of 63.2 years, who had enrolled in a clinical trial of beta carotene supplementation to prevent nonmelanoma skin cancer. Eighteen percent of the subjects were smokers. During a median follow-up period of 8.2 years, the study reports, researchers tabulated 285 deaths.

In order to determine pre-supplementation beta carotene levels, researchers took blood samples from participants at the start of the study. Subsequently, participants were randomly assigned to receive either a daily 50 mg beta carotene supplement or a placebo.

The researchers stated that "one cannot firmly conclude from these data that beta carotene supplementation is entirely without benefit." Achieving a benefit from supplementation, they said, might require a longer duration of supplementation and follow-up. However, "if beta carotene actually requires many years to become effective," states the study, "there may be little enthusiasm for taking it, particularly among older adults."

Another possible explanation, Greenberg et al. noted, is that "beta carotene has beneficial effects but that they are too small to be detected in a study of the size we conducted."