Elevated levels of total and low density lipoprotein (LDL) are a risk factor for cardiovascular disease. Reductions in serum cholesterol levels of 1% reduce the risk of cardiovascular disease by 3%. However, cause and effect are not proven and it is far from certain that cholesterol is implicated in the aetiology of cardiovascular disease. Instead it is likely that cholesterol levels become elevated when metabolic abnormalities occur, these abnormalities leading to the development of cardiovascular disease. This would explain why a such wide range nutrients with differing mechanisms of action seem to be able to lower circulating cholesterol levels and why elevated cholesterol levels are only a risk factor for cardiovascular disease in some sub-populations. Green tea is protective of cardiovascular disease and this was originally thought to be due to its antioxidant ability in vivo. However, green tea is also able to lower cholesterol levels.
A number of research studies have suggested that green tea has beneficial blood lipid lowering properties. Researchers1 have performed a meta analysis on studies investigating the effects of green tea on cholesterol levels and included 14 eligible papers. Studies included had cross-over randomised designs, were for a duration of >2 weeks and had the primary outcome as changes in total, LDL and HDL cholesterol levels. The total number of subjects in the meta analysis was 1136. The results showed that green tea consumption significantly lowered the total cholesterol concentration by 7.20mg/dL and also significantly lowered the LDL cholesterol by 2.19mg/dL. There were no significant changes in HDL cholesterol in the analysis. Interestingly, analysis of sub-groups and the doses of green tea did not show any variation in the effects, suggesting that tea consumption is beneficial even when considering fixed models of consumption.
Tea is well established as being beneficial to the cardiovascular system in the scientific literature. Large studies from Japan show beneficial effect of drinking more than 2 cups of tea a day, compared to non-tea drinkers. The mechanisms by which green tea can lower cholesterol levels is not fully understood, but animal experiments show that the catechins in green tea containing gallate esters are able to form insoluble precipitates of cholesterol and this interfere with the billary reabsorption of cholesterol. This may then increase LDL receptor expression on hepatocytes and remove more LDL cholesterol from circulation. Increased LDL receptor and lower circulating LDL cholesterol numbers have been reported in animal studies feeding catechins in rats. In addition, catechins may have direct inhibitory effects of cholesterol synthesis and in vitro evidence suggests they may inhibit squalene epoxidase, a rate limiting enzyme in cholesterol synthesis.
RdB
