Chicago ? Can drinking green tea really protect against two big killers, strokes and cancer? A huge study in Japan suggests yes and no: It might lower your stroke risk but won’t save you from cancer.

The study’s authors say their findings might explain why the Japanese are less likely than Americans to die of heart disease and stroke. Even so, the answers aren’t clear. Green tea has been researched a lot, and many of the studies have come up with conflicting results.

Tea contains substances called antioxidants that can help keep cells healthy. Green tea has more of them than black tea, and studies in animals have shown that tea antioxidants called catechins seem to shrink cancerous tumors. Some studies in humans have suggested tea can also help keep arteries and cholesterol healthy.

The current study was funded by the Japanese government and is published in today’s Journal of the American Medical Assn. It’s different from many previous studies because it involved so many people – 40,530 Japanese adults. Those who drank lots of green tea were less likely than those who drank only a little tea to die from cardiovascular disease and other causes, but not cancer.

Because tea-drinking is popular among Japanese people from all lifestyles and economic groups, the research seems to refute a criticism of previous studies – that people who drink green tea are higher income and more health-conscious and thus apt to be healthier anyway.

Study participants were generally less overweight than Americans, and it’s unknown if similar results would be found in a more diverse group of people, said Alice Lichtenstein, a Tufts University nutrition professor and spokeswoman for the American Heart Assn.

The results from this study, which observed people and their habits over several years, “point you in a direction” but aren’t conclusive, she said.