Scientists from Zhejiang University in the People’s Republic of China report that the apparent benefits were even more significant in people with a higher cardiovascular risk, like hypercholesterolemia.
“It has been reported that 1 mg/dL reduction of LDL cholesterol concentration can reduce coronary artery disease risk by 1%, therefore a 4.64 mg/dL reduction of serum LDL cholesterol concentration [as reported in this meta-analysis] is of both statistical significance and clinical importance,” they wrote in the journal Clinical Nutrition .
While the majority of science on tea has looked at green tea, there is a growing body of research that supports the health benefits of black tea.
Green tea contains between 30 and 40% of water-extractable polyphenols, while black tea (green tea that has been oxidized by fermentation) contains between 3 and 10%. Oolong tea is semi-fermented tea and is somewhere between green and black tea. The four primary polyphenols found in fresh tealeaves are epigallocatechin gallate (EGCG), epigallocatechin, epicatechin gallate, and epicatechin.
The Chinese scientists report that catechins from black tea may be regulating LD cholesterol by inhibiting the absorption of cholesterol in the intestine while also increasing the rate of conversion of cholesterol to bile acids.
“Black tea polyphenols are also shown to suppress cholesterol biosynthesis and to promote the expression of LDL cholesterol receptor,” they wrote. “Apart from lowering LDL cholesterol, black tea can protect against cardiovascular disease via other pathways like through its antioxidant and antifibrinolytic property.”
Beverage vs extracts
Led by Dr Duo Li, the researchers analyzed data from ten randomized trials that involved 411 adults. Results indicated that black tea consumption of black tea was associated with significant reduction in LDL cholesterol levels of, on average, 4.64 mg/dL. On the other hand, no significant effects were observed for HDL and total cholesterol.
The researchers noted that the benefits of the black tea appeared to be linked to how it was delivered, with extracts outperforming the beverage. “However, we cannot assert that, black tea extract is better than black tea beverage in regulating LDL cholesterol concentration at this stage,” they wrote. “Only two of the nine trials adopted black tea extract as intervention trials and limited number of included studies in this subgroup could tender the statistical strength of the results.
“Therefore, further research is needed to explore whether there is appreciable difference between black tea beverage and black tea extract in improving serum cholesterol profile and enhancing human health.”
Source: Clinical Nutrition
Published online ahead of print, doi: 10.1016/j.clnu.2014.06.003
“Black tea consumption and serum cholesterol concentration: systematic review and meta-analysis of randomized controlled trials”
Authors: Y. Zhao, S. Asimi, K. Wu, J. Zheng, D. Li