A topic in Clinical Evidence 2 summarizes the evidence on antioxidants for the secondary prevention of ischaemic cardiac events. Pooled analysis found four large RCTs that yielded no evidence of the effectiveness of vitamin E over placebo when given for 1.3 - 4.5 years. Pooled analysis from three small RCTs found no evidence that vitamin C provided any substantial benefit. Large RCTs found no evidence on benefit of beta carotene, and one RCT found evidence of a significant increase in mortality. Four large RCTs of beta carotene supplementation in primary prevention found no cardiovascular benefits, and two of the RCTs raised concerns about increased mortality. Clinical evidence category: Unknown effectiveness (vitamin E, vitamin C). Likely to be ineffective or harmful: beta carotene.
A systematic review 1 including 18 studies on vitamin E, vitamin C and beta-carotene with a total of 295,311 subjects was abstracted in DARE.
Large, prospective cohort studies suggest that overall there is a lower risk of cardiovascular disease for vitamin E users, but there are several inconsistencies in the data. The evidence from large, prospective epidemiological studies of beta-carotene were somewhat inconsistent, but did suggest the possibility of lower adverse cardiovascular outcomes particularly for men who are current smokers, but randomised trials do not support this, and beta-carotene may be associated with an increased risk of cancer. For vitamin C, the evidence from epidemiological studies is inconclusive.
Comment: The quality of evidence is downgraded by inconsistency of results and study limitations.
Primary/Secondary Keywords