Experts believe it is the polyphenols in green tea that may make it beneficial
Drinking green tea may offer some protection against lung cancer, say experts who studied the disease at a medical university in Taiwan.
The latest work in more than 500 people adds to growing evidence suggesting the beverage has anti-cancer powers.
In the study, smokers and non-smokers who drank at least a cup a day cut their lung cancer risk significantly, a US cancer research conference heard.
The protection was greatest for people carrying certain genes.
But cancer experts said the findings did not change the fact that smoking is bad for health.
Green tea is made from the dried leaves of the Asian plant Camellia sinesis and is drunk widely across Asia.
The rates of many cancers are much lower in Asia than other parts of the world, which has led some to link the two.
Laboratory studies have shown that extracts from green tea, called polyphenols, can stop cancer cells from growing.
But results from human studies have been mixed. Some have shown a protective effect while others have failed to find any evidence of protection.
In July 2009, the Oxford-based research group Cochrane published a review of 51 studies on green tea and cancer which included over 1.5 million people.
They concluded that while green tea is safe to drink in moderation, the research so far is conflicting about whether or not it can prevent certain cancers.
Dr I-Hsin Lin, of Shan Medical University, found that among smokers and non-smokers, people who did not drink green tea were more than five times as likely to get lung cancer than those who drank at least one cup of green tea a day.
Among smokers, those who did not drink green tea at all were more than 12 times as likely to develop lung cancer than those who drank at least a cup a day.
Researchers then analysed the DNA of people in the study and found certain genes appeared to play a role in the risk reduction.
Green tea drinkers, whether smokers or non smokers, with certain types of a gene called IGF1, were far less likely to develop lung cancer than other green tea drinkers with different types of this gene.
Yinka Ebo, of Cancer Research UK, said the findings should not be used as an excuse to keep smoking.
"Smoking tobacco fills your lungs with around 80 cancer-causing chemicals. Drinking green tea is not going to compensate for that.
"Unfortunately, it's not possible to make up for the harm caused by smoking by doing other things right like eating a healthy, balanced diet.
"The best thing a smoker can do to reduce their risk of lung cancer, and more than a dozen other cancer types, is to quit."