β-Carotene and risk of coronary heart disease. A review of observational and intervention studies

The production of free radicals may favour the processes of atherosclerosis, and antioxidant vitamins (including β-carotene), which partly prevent such processes, might favorably influence cardiovascular disease (CVD); thus, their supplementation might be a useful tool in the prevention of coronary heart disease (CHD). The relationship between β-carotene and CHD has been investigated in several observational studies, including ecological, cohort and case-control studies. Six cohort studies reported relative risks (RR) of CHD between 0.27 and 0.78 for high β-carotene levels (plasma/serum levels and dietary intake), but four more recent ones reported RR around unity (range 0.84 to 1.19). The evidence from case-control studies supports a role of β-carotene in the prevention of CHD (odds ratios, OR, between 0.37 and 0.71), with a possible stronger protection for current smokers. The four published randomized clinical trials of β-carotene supplementation found RR close to unity (range 0.96 to 1.26) for the relation between β-carotene and CHD. The apparent discrepancy between observational and intervention studies may depend on several factors. The benefit reported in some observational studies may be related to consumption of foods rich in β-carotene rather than β-carotene itself, as foods rich in β-carotene are usually rich also in other antioxidant vitamins and micronutrients, or to time-related factors, i.e., longer supplementation in intervention studies. Thus, a reasonable recommendation for the prevention of CHD for the general population is to consume a balanced diet with emphasis on antioxidant rich fruit and vegetables and whole grains.