Long Life May Be Your Cup of (Green) Tea
The brew helps prevent an early demise, major Japanese study suggests
TUESDAY, Sept. 12, 2006 (HealthDay News) -- For those hoping to live a long, healthy life, a cup of green tea may hit the spot, a large new study shows.
Adults who drank at least five cups of the brew daily had a lower risk of cardiovascular death and death from all other causes, except cancer, than those who drank less than one cup a day, according to a research team from Tohoku University in Sendai, Japan.
They published their findings in the Sept. 13 Journal of the American Medical Association.
While many laboratory and animal studies have suggested that green tea protects against illness, its effect in humans has been less clear.
"Only four epidemiological studies [in people] have been conducted to date," said lead researcher Dr. Shinichi Kuriyama.
And those studies "included small sample sizes, and the results were inconsistent," he added.
However, "our study includes far more participants -- 40,350 -- than the previous studies," Kuriyama said. "I think our study would provide strong evidence regarding the benefits of drinking green tea in humans on cardiovascular disease."
Beginning in 1994, his team tracked the health of adults aged 40 to 79 living in northeastern Japan, where green tea is a popular beverage. The participants had no history of heart disease, stroke or cancer when they started the study.
The researchers tracked death from all causes for 11 years and also tracked deaths linked to specific causes for a 7-year period.
More than 4,000 of the participants died over the total 11 years of follow-up, the research team reported. During the 7 years of the study that focused on specific causes, 892 people died from cardiovascular disease and 1,134 from cancer.
Comparing death rates and green tea consumption, Kuriyama's team found that individuals who drank five or more cups per day had a risk of death from all causes that was 16 percent lower than people drinking less than one cup per day.
Deaths from cardiovascular disease were 26 percent lower for tea drinkers vs. those who avoided the beverage.
These effects were even stronger among women. Women who drank five or more cups of green tea per day had a 31 percent lower risk of death from heart disease and stroke death compared to women who drank less than a cup a day.
Green tea appeared to have no effect on cancer risk, however. The researchers also saw only a weak or negligible effect on death rates for people who drank black or oolong teas.
"The reason for the discrepancy between effects on cardiovascular disease and on cancer death in our study is uncertain," Kuriyama said. Other human trials have also failed to find any effect between green tea consumption and cancer, he noted.
How does green tea work its heart-healthy magic? Experts believe natural compounds called polyphenols -- particularly one substance called epigallocatechin-3-gallate -- provide the health benefits. These substances have strong antioxidant properties that may help prevent heart disease.
The study was funded by the Japanese Ministry of Health, Labor and Welfare.
Another expert, Dr. Kuang-Yuh Chyu, an assistant professor of medicine at the University of California, Los Angeles, and a staff cardiologist at Cedar-Sinai Medical Center, Los Angeles, said the study, while interesting, is only "observational data."
One of the problems with this type of study, he explained, is that "you can't control for a lot of things."
"To be more definitive, we need a randomized trial," said Chyu. He said his lab's animal studies have found that green tea does have cardio-protective effects, especially if consumption commences before the onset of hardening of the arteries.
For those who might want to "go green" for health, "I'd probably take a neutral position right now," Chyu said.
"Tea is not harmful, that we know," he said. If you're a tea drinker, continue, Chyu said. If not, be aware that the habit probably needs to be long-term before you reap any real health benefit.
"I don't think I'd recommend people drink large quantities of green tea," added Dr. Robert Vogel, professor of medicine at the University of Maryland Medical School.
Like Chyu, he stressed that the study only showed an association, not any direct cause-and-effect. However, he said green tea consumption is certainly preferable to drinking beverages such as non-diet sodas, which are loaded with sugar.
U.S. government health agencies have so far backed away from recommending green tea as a health aid. Earlier this year, a U.S. Food and Drug Administration review of the available data found no evidence to support companies' claims that green tea eases cardiovascular risk. The agency released a similar statement in 2005, noting a lack of evidence that green tea fights cancer.
Experts at the U.S. National Cancer Institute have also reviewed data from human trials focused on tea's cancer-preventing effects but said the studies offered conflicting results. The NCI is funding its own rigorous studies on the subject, however.
The study's lead author was much more enthusiastic.
"I personally drink green tea, two or three cups per day," Kuriyama said. "On the basis of our study results, I would like to recommend the drinking of green tea at least one cup per day."
But Kuriyama added that the tea should not be steaming hot. "Drinking green tea at high temperature may be associated with increased risk of esophageal cancer and mortality," he said, citing two published studies.
To learn more about how antioxidants work, visit the American Heart Association.