Positive Health Online

Abstract

WANG and RUSSELL, Jean Mayer USDA Human Nutrition Research Center on Aging, Boston, MA, USA write that a large body of observational epidemiological studies has consistently demonstrated that individuals who eat more fruits and vegetables, which are rich in carotenoids, and people with a higher serum beta-carotene levels have a lower risk of cancer, particularly lung cancer . However, two human intervention studies which used high-dose beta-carotene supplements reported an increased risk for lung cancer among smokers. The authors review (82 references) the evidence in this contentious field.

Background

Methodology

Results

and Discussion: Recent in vitro and in vivo studies have shown that beta-carotene itself may act as an anticarcinogen, but its oxidised products may actually facilitate carcinogenesis . This research supports the hypothesis that the carcinogenic response to high-dose beta-carotene supplementation reported in the human intervention trials is related to the instability of the beta-carotene molecule in the free radical-rich environment in the lungs of cigarette smokers . This is especially possible because smoke also causes decreased tissue levels of other antioxidants, such as ascorbate and alpha-tocopherol, which usually have a stabilizing effect upon the unoxidized form of beta-carotene.

Conclusion

Nutritional intervention using a combination of antioxidants (beta-carotene, alpha-tocopherol and vitamin C) as anticarcinogenic agents, may be an appropriate way to rationally and realistically reduce cancer risk.

References

Wang XD and Russell RM. Procarcinogenic and anticarcinogenic effects of beta-carotene. Nutrition Reviews 57(9 Pt 1): 263-72. Sep 1999.

Comment

This is a highly important review, due to the sensational publicity which attended the original publication of the Finnish Beta-Carotene Study several years ago. Beta-carotene, in the "free radical-rich environment" of a smokers lungs, may be unstable and its oxidised products may contribute to carcinogenesis. Particularly as smoking also decreases levels of other potent antioxidants including vitamins C and E. For another study demonstrating yet other horrific effects of cigarette smoking, please also see Zhang et al under Nutritional Status.