The finding may explain why green tea has been linked to a lower risk of heart disease, write Xin-Xin Zheng and colleagues from Peking Union Medical College in Beijing.
While levels of low-density lipoprotein (LDL) cholesterol dipped, there was no change in high-density lipoprotein (HDL), or "good" cholesterol.
"The analysis showed that the administration of green tea beverages or extracts resulted in significant reductions in serum total cholesterol and LDL-cholesterol concentrations, but no effect on HDL cholesterol was observed," they wrote in the American Journal of Clinical Nutrition.
The research team pooled the results of 14 randomized trials in which participants drank green tea or took an extract for periods ranging from three weeks to three months, or were assigned to a placebo group.
On average, green tea reduced total cholesterol by 7.2mg/dl (milligrams per decilitre) compared with levels seen in those taking the placebo. Low density lipoprotein (LDL) cholesterol fell by a mean of 2.2 mg/dl, or slightly less than two per cent.
The cholesterol-lowering effects of green tea may be due to catechins, which decrease the absorption of cholesterol in the gut, the researchers said.
But this reduction is fairly small, warned Nathan Wong, who runs the heart disease prevention program at the University of California, Irvine. Green tea "should not be recommended in place of well-proven cholesterol-lowering medicines for people with high cholesterol," he told Reuters Health.
Some researchers have raised concern over possible side effects from heavy consumption of green tea or green tea extracts. There have been a few dozen reports or liver damage, and green tea may also reduce the effectiveness of some medications. But Wong said that smaller amounts "could be a useful component of a heart-healthy diet," with benefits that go beyond its effect on cholesterol.
Green tea has been linked to a lower risk of developing certain forms of cancer as well as reducing the risk of dying from pneumonia.
From the July 11, 2011, Prepared Foods' Daily News.