Wednesday, 23 November 2011 11:11
Green tea, in a cup or a capsule, may shave off a few points of your "bad" cholesterol, a new research review suggests.
Looking at 20 past clinical trials, researchers found that green tea trimmed 5 to 6 points more from people's total cholesterol and "bad" LDL cholesterol levels than dummy capsules or other inactive treatments.
The trials tested either green tea itself or capsules containing green-tea compounds called catechins, which are thought to decrease cholesterol absorption in the gut.
In general, green tea in a cup was more consistently effective than capsules. But the benefits overall were fairly small.
"The analysis suggests there is only a modest effect of green tea on cholesterol levels," said senior researcher Olivia J. Phung, an assistant professor of pharmacy at Western University of Health Sciences in Pomona, California.
LDL cholesterol is considered optimal when it is below 100 milligrams per deciliter, whereas 160 mg/dL or more is considered high.
The researchers found no strong evidence that green tea boosted "good" HDL cholesterol, or cut triglycerides, another type of blood fat. So for people who have high cholesterol, green tea is no replacement for medication, Phung told Reuters Health in an email.
"If someone is already taking medication for their cholesterol," she said, "they should stick with it and not try to trade it for green tea -- either capsules or the beverage."
On the other hand, Phung noted, adding green tea to your diet could be one way to further improve your cholesterol numbers.
But green tea is not a dietary magic bullet. To keep your cholesterol in check, experts recommend getting plenty of high-fiber grains, fruits and vegetables, and limiting saturated fat (from meat and full-fat dairy) in favor of "good" fats from fish and vegetable oils.
A good number of clinical trials have examined whether green tea, or green tea extracts, can benefit people's cholesterol levels. But they have come to mixed conclusions. One problem is that most of those trials have been small, which makes the findings less reliable.
So for their study, published in the Journal of the American Dietetic Association, Phung's team pooled the results of 20 clinical trials that involved a total of 1,415 adults.
In all of the trials, participants were randomly assigned to either use green tea everyday (as a beverage or capsule) or be part of "control" groups that took placebo capsules, drank a low-catechin tea or downed water in lieu of tea.
The trials lasted anywhere from three weeks to six months, with the green-tea users showing a bigger average decline in LDL and total cholesterol than their counterparts in the control groups.
The benefit seemed to be limited to people who already had high cholesterol when they entered the study.
Overall, teas appeared more effective than capsules. But Phung said there isn't enough data to be sure that the beverage is better than the extract.
"We would really need to have some head-to-head studies comparing the different forms of green tea in order to show which ones work more effectively," Phung said.
There are other questions, too—including what dose of green tea catechins is "ideal."
In the trials Phung's team studied, the daily catechin dose ranged from 145 milligrams to 3,000 milligrams. But the researchers were not able to test for a "dose-response" effect—which would have shown whether the cholesterol benefits increase as the catechin dose goes up.
As for side effects, green tea is considered safe in moderate amounts—though the drink and the extracts contain caffeine, which some people may need to avoid.
There have also been a few dozen cases of liver damage reported among people using green tea extracts, but it's not certain that the supplements are to blame.
The current study had no industry funding, and none of the researchers reports financial conflicts of interest.
By Amy Norton
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