Health Canada and CBC say green tea extract causes liver damage

Health Canada is making warnings about the risk of liver injury with green tea extract more explicit. But, here's what you need to know.

Their safety review, however, states that “The vast majority of those who consume green tea, in any form, do so without harm.” While Health Canada undertook the review because of eleven cases of suspected liver injury associated with products containing green tea extract, it concedes that only two of these cases “had enough information to be fully assessed.” So, that’s two, not eleven. And, for those two, the conclusion could only be reached that the liver injury was “potentially” related to use of products containing green tea extract. So, that’s zero, not two.

When Health Canada searched the World Health Organization Adverse Drug Reaction Database, it found only 89 reports any where in the world of liver injury associated with the use of green tea extract containing products. And not one of them had enough information to properly assess. So, that’s zero again.

Canada’s CBC news not only does a highly selective and incomplete job of researching the story, it also consistently goes on to make the claim that green tea is not even effective for weight loss, which is one—but only one—of the reasons that many people use it. CBC cites epidemiologist Jason Busse, who says, “the research couldn't determine whether green tea actually contributed to weight loss.” Amazingly, they the cite the highly referenced and scientific opinion of Dr. Sean Wharton, who dismisses all weight-loss supplements as “fake medicine” and “hope in a bottle.”

As for no research showing green tea actually contributes to weight loss, a meta-analysis of 11 studies on green tea and weight loss and weight maintenance concluded that green tea catechins significantly decrease body weight and significantly benefit the maintenance of body weight (International Journal of Obesity 2009;33:956–961).

Green tea helps weight loss by stimulating thermogenesis (Am J Clin Nutr1999;70:1040-5). Green tea especially targets weight loss in the waist, which is important because losing weight in the abdominal area may be the most important kind of weight loss for living longer healthier lives (Ann Intern Med 2015;doi:10.7326/M14-2525). Obese women who were given 250mg of powdered green tea eight times a day in a double-blind, placebo-controlled study, lost 1.9kg in 30 days and significantly decreased their waist measurement (Revue De L’assoc Mondiale de Phytother1985;1:36-40). A study which gave green tea extract to moderately obese people produced a 4.6% decrease in weight and a 4.5% decrease in waist size in three months (Phytomedicine 2002;9:3–8). Overweight men and women who did not exercise were put on an exercise program and given either green tea that had its catechin content enriched or a placebo beverage. Abdominal fat went down by 7.7% in the green teagroup and only by 4.4% in the placebo group (J Nutr 2009;2:264-70).

Green tea containing 583mg of catechins was compared to green tea containing only 96mg of catechins in a 12 week double-blind study of 240 obese people. The 96mg catechin group served as a control. The higher catechin green tea group had significantly greater improvement in body weight, body mass index, body fat ratio, body fat mass, waist circumference, hip circumference. No adverse effects were found (Obesity 2007;15:1473-1483).

A placebo-controlled study of 182 moderately overweight people gave either a control green tea low in catechins or various higher catechin content green teas for 90 days. The highest dose catechin green tea significantly decreased intra-abdominal fat. Compared to the control group, the high catechin green tea led to a significant 1.9cm decrease in waist circumference and a significant 1.2kg loss in weight (Obesity 2010;18:773-9).

One of the hardest parts about weight loss is that, after the diet program, after the initial period of weight loss, the weight just comes back again. This novel study looked at the ability of green tea extract to keep the weight off after the weight loss program. The study 55 men and women who had just undergone an 8 week weight loss phase of the study, during which they lost a significant amount of weight. To see if green tea could help them maintain the weight loss, half the people were given a rye bread placebo, and the other half were given rye bread with 1.1% green tea added to the bread. After the weight maintenance phase of the study, mean body weight went back up by 1.5kg (3.3lbs) in the rye bread group but by only 0.6kg (1.3lbs) in the green tea group, meaning that the green tea helped them keep the weight off. The effectiveness of greentea was also shown by waist circumference increasing again significantly less in the green tea group (J Med Food 2015;18:698-705).

All of these studies show, not only that green tea is effective for weight loss, but that it is effective for the especially healthy abdominal weight loss (waist circumference).

As for the safety of green tea extracts, if CBC and Health Canada did their research, they would see that the research has already been done.

The researchers say that the case for green tea as a potential liver toxin is based on animal studies in which high doses of some green tea extracts were used and on reports of humans who consumed excessive doses of green tea supplements. Because this data is based on animal studies and human cases involving excessive doses, the researchers undertook a systematic review of published controlled human studies of green tea extracts and liver safety and published it in the peer reviewed European Journal of Clinical Nutrition.

34 studies were eligible for inclusion in the systematic review. 28 assessed efficacy and 6 measured the safety of green tea. 24 of the studies were double-blind, 6 were single blind and only 4 were open-label. Of the 19 studies that were double-blind and placebo controlled, 13 of them assessed the effect of green tea on liver function (liver disease, AST, ALT, ALP). 

Liver related adverse events occurred in only 0.5% of cases, and not one of the was serious. 

Adverse events were rare and not serious, and often likely had nothing to do with the green tea. In a study of 36 healthy men, slightly elevated ALT was found in one man taking the highest dose (800mg) of EGCG. But the researchers judged that the slight elevation had nothing to do with the green tea. Within 2 weeks of study completion, his values had returned to normal (Int J Vitam Nutr Res. 2004;74(4):269-278). 

In a study of menopausal women and green tea polyphenols, 1 out of 85 women receiving 500mg of green tea polyphenols had elevated AST and ALT levels. However, the researchers concluded that the elevations were unrelated to the green tea (they suspected cold medications to be the cause) (BMC Complement Altern Med 2010;10:76).

A study that gave green tea extract to 40 women with a history of breast cancer used high dose EGCG. There was 1 case of mildly elevated ALP in the 800mg group, 1 case of mildly elevated ALP in the 1200mg group, and 1 case of mildly elevated AST and ALT and 1 case of severely elevated ALT in the 1600mg group (Cancer Prev Res (Phila)2012;5(9):1144-1154).

And a study of 50 men with prostate cancer found that only one man on an 800mg dose of EGCG developed a mild elevation of ALT (Cancer Prev Res (Phila) 2012;5(2):290-298).

The authors of the systematic review conclude that "the results of the present review suggest that liver-related adverse events after intake of green tea extracts are expected to be rare (Eur J Clin Nutr 2016;70(11):1221-1229)."

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