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Excessive consumption of green tea may be unhealthy, study finds

9 December 2015  •  Author(s): Victoria White

Researchers from the University of California, Irvine (UCI) have discovered that excessive consumption of green tea adversely affect the development and reproduction in fruit fly populations.


It is unclear whether over-consumption could have the same impact on humans, but the findings suggest caution when using green tea, or any natural product, in high doses. Nutraceuticals, while growing in popularity, are largely unregulated.

A UCI team led by Mahtab Jafari, associate professor of pharmaceutical sciences, investigated the effects of green tea toxicity on Drosophila melanogaster development and reproduction. Embryos and larvae were subjected to various doses of tea polyphenols.

Larvae exposed to 10 milligrams of green tea were slower to develop, were born smaller and exhibited a dramatic decline in the number of emerged offspring. Ten milligrams also made the flies more susceptible to starvation and heat stress but protected them against dehydration. Female offspring showed decreased reproductive output and a 17% reduction in lifespan; males were unaffected. In addition, 10 milligrams of the tea caused morphological abnormalities in reproductive organs, such as testicular and ovarian atrophy.

Jafari believes that high doses of green tea may cause “too much” apoptosis, or cell death, but in this study, she said, they did not evaluate mechanisms, which is the focus of her current research.

Reports of problems associated with excessive consumption of green tea

Green tea is popular worldwide for its purported brain and heart health and anticancer properties. However, there are some reports of problems associated with excessive consumption: Jafari noted that in other tests with mice and dogs, green tea compounds in large amounts dramatically reduced body weight and, in mice, negatively affected embryo development.

“While green tea could have health benefits at low doses, our study and others have shown that at high doses, it may have adverse effects,” she said. “Further work is needed to make any definite recommendations, but we can suggest that green tea be consumed in moderation.”

“We are planning to continue to measure total consumption, evaluate metabolic pathways, and identify and quantify the metabolites of natural products in flies,” Jafari said. “These experiments will enable us to have a better understanding of toxic doses in humans.”

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