Green tea and green tea catechin extracts: an overview of the clinical evidence.

BACKGROUND: Tea leaves contain varying amounts of polyphenols of which the majority are catechins. There has been a sizable amount of research on the potential effect of green tea catechins for cancer risk, cardiovascular disease risk and weight loss; all conditions that are relevant to mid-life health. The aim was to produce an overview of the evidence for green tea for these three important health conditions.

METHODS: The databases Medline (& Medline in process) and Embase, were searched for systematic reviews and meta-analyses using customised search strategies performed up until April 2012. Assessment of Multiple Systematic Reviews criteria were used to assess the quality of the included reviews. Relevant data were extracted into predefined tables. The results are described and discussed narratively.

RESULTS: We included eight systematic reviews and meta-analyses covering the topics of cancer risk (n=2), cardiovascular risk (n=4) and weight loss (n=2).

CONCLUSIONS: The evidence for green tea and cancer risk is inadequate and inconclusive. However there is some positive evidence for risk reduction of breast, prostate, ovarian and endometrial cancers with green tea. RCTs of green tea and cardiovascular risk factors suggest that green tea may reduce low-density lipoproteins and total cholesterol, although studies are of short duration. There is no robust evidence to support a reduction in coronary artery disease risk in green tea drinkers. There are a considerable number of RCTs to suggest that green tea does reduce body weight in the short term, but this not likely to be of clinical relevance.