Tea is in. In the past few years, more and more Filipinos have developed a taste for tea.
That makes it now the country’s fourth most popular beverage, after water, soft drinks, and coffee.
And green tea extracts are the fastest growing dietary supplements.
There’s no doubt that tea is an invigorating drink – you can probably credit its caffeine for that (tea has about half the caffeine of coffee).
And the national waistline would be far better off if we replace some of that soda with tea (provided we sip it with little or no sugar).
But does tea lower the risk of cancer, heart disease, and obesity, as some manufacturers claim? Let’s check the tea leaves.
Heart Disease
“Tea drinking is associated with improved cardiovascular health,” says the Tea Association’s Web site. Yet the U.S. Food and Drug Administration (FDA) concluded in 2006 that “there is no credible scientific evidence” that green tea can reduce the risk of heart disease. (The evidence for black tea isn’t good, either.) Who’s right? “It’s confusing when you look across all the epidemiological studies,” says tea researcher David Maron of the Vanderbilt Heart Institute in Nashville, Tennessee. “Some studies find that drinking tea is linked to less cardiovascular disease, some do not, and some actually find an increased risk from drinking tea.”
Clearly, though, the Tea Association isn’t confused. According to the industry group’s Web site, a University of North Carolina analysis of more than a dozen published studies “found an average estimated 11 percent lower rate of heart attacks among study participants who drink three or more cups of tea per day.” The tea folks fail to disclose that the studies’ results were so contradictory that, statistically, the 11 percent reduction was no different from a zero reduction. But what if three cups a day aren’t enough? Apparently, neither are five cups, at least not in the most recent large studies that looked at the health of tea drinkers.
Among 40,000 healthy middle-aged and older Japanese men and women, those who drink five or more cups of green tea a day were just as likely to die of heart disease during an 11-year period as those who drank less than one cup a day. Unfortunately, clinical studies – which give people tea or a placebo and wait to see what happens – are scarce. “There really is not a lot of evidence from good clinical trials,” notes Maron. “None have looked at whether drinking tea or taking tea extracts prevent heart disease or strokes, and only a few have looked at whether it lessens any risk factors.”
In 2006, the FDA reviewed the evidence after a Japanese company asked for permission to say on its labels that its green tea could lower the risk of heart disease. In the seven good clinical studies submitted by the company, green tea or green tea extracts did nothing to lower cholesterol or blood pressure. The FDA denied the company’s petition.
However, a 2003 clinical study found that 114 men and women who took a tea extract called Teaflavin every day for three months ended up with LDL (“bad”) cholesterol levels that were 15% lower than those of 114 similar people who were given placebo. But the Teaflavin takers were getting the equivalent of 35 cups of tea a day. (Teaflavin combines the antioxidants theaflavin from black tea and catechins from green tea.) “It’s ridiculous to try to lower cholesterol levels by drinking tea because you would have to drink dozens of cups every day,” says David Maron, who conducted the study for Teaflavin’s manufacturer. “If someone can’t lower cholesterol by diet - or can’t or doesn’t want to use prescription statin drugs - then I would say he or she could try this extract to see if it helps.”
Bottom line: Drinking tea doesn’t appear to prevent heart disease. While one brand of tea extract lowered LDL (“bad”) cholesterol in one published study, that’s not enough to conclude it works.
Cancer
In the 1990s, tea seemed like a miracle cancer-fighter. “There’s no agent in the literature that has shown such remarkable effects in so many animal systems,” Hassan Mukhtar of Case Western Reserve University in Cleveland said in 1994. He was then hardly exaggerating. When researchers gave animals carcinogens, tea extracts reduced the number of tumors in the breast, colon, prostate, pancreas, skin, lung, esophagus, and small intestine. But what was missing 10 years ago is still missing today: evidence that tea also prevents cancer in people.
“While most of the animal studies that have been reported have been positive, the epidemiological data are not clear in finding a benefit for tea on cancer in humans,” says researcher Joshua Lambert of Rutgers University in New Jersey. For example, in that study of 40,000 healthy middle aged and older Japanese men and women, those who drank five or more cups of green tea a day were just as likely to die of cancer during an 11-year period as those who drank less than one cup a day. As for specific cancers:
• Colon. In 28 studies on three continents, people who drink the most black or green tea were just as likely to get colon cancer as those who drank the least.
• Prostate. In the most recent study, which looked at 19,000 Japanese men, those who drank five or more cups of green tea a day were as likely to die of prostate cancer as those who drank less than one cup a day. “The epidemiological evidence for black or green tea protecting against prostate cancer is not very strong,” says Anna Wu of UCLA.
• Breast. “Studies show that drinking black tea has no effect on breast cancer,” says Wu. In 13 studies in eight countries involving more than 160,000 women, those who drank the most black tea, usually four or more cups a day, were just as likely to be diagnosed with breast cancer as those who drank the least. For green tea, “the evidence isn’t very strong, either,” says Wu. In three studies that tracked nearly 70,000 Japanese women for seven to 24 years, those who drank at least five cups of green tea daily were just as likely to be diagnosed with breast cancer as those who drank little or none. But, says Wu, “We need additional human studies that carefully document the intake in order to draw strong conclusions about green tea and breast cancer.”
Why is the evidence that tea prevents cancer so strong in animals and test tubes, yet so weak in humans? “How much tea people consume versus how much is used in the animal experiments has always been a key issue,” says Rutgers’ Joshua Lambert. As a result, the concentration of those ingredients in the animals’ tissues may be 10 times higher than in the tissues of people who drink tea.
“When you look at the animal studies that use levels of tea more comparable to the concentrates found in human tissues, you don’t see an anti-cancer effect,” says Nurulain Zaveri of SRI International, a nonprofit institute in Menlo Park, California, that conducts research for industry and the government. “I think the value of the research we’re doing will be identifying how tea prevents cancer in animals and test tubes, and then developing drugs to do the same thing,” she says.
Bottom line: Tea prevents cancer in animals but in human studies, people who drank five more cups a day have no lower risk. Few studies have tested tea extracts on cancer in people.
Weight
In late 2006, two companies in the US marketed a carbonated diet green tea fortified with 100 mg of caffeine and 90 mg of epigallocatechin gallete (EGCG), an antioxidant that occurs naturally in tea. The companies claim that you can burn an additional 60 to 100 calories every 24 hours if you drink three 24-ounce cans daily.
So, does tea – or EGCG in tea – have any impact on weight? The evidence is pretty thin. In a handful of small studies that lasted only one to three days, people who took EGCG plus caffeine burned slightly more calories than those who were given placebo. But what happens after a few days? Do people eat more to compensate for the extra calories they’re burning, or perhaps stop burning extra calories? The results of the studies showed there was no difference between those who drank tea and those who took placebo after 12 weeks.
Bottom line: In a few very-short-term studies, people burned slightly more calories when given EGCG plus caffeine. But in longer-term studies, the combination had no consistent impact on weight.
While there may be other health benefits for tea, there is currently no concrete scientific evidence that drinking tea is beneficial for heart disease, cancer, or weight loss.