What Scientists Are Saying About Drinking A Lot Of Tea

Last month, the Health Council of the Netherlands, an independent scientific body that advises the Dutch government, issued new national dietary guidelines. Most of them were run-of-the-mill tips: Eat balanced meals; limit alcohol intake; embrace nuts and fish oils. But one recommendation caught observers' eyes. According to the Council, everyone ought to drink three to five cups of tea a day—and they mean the hard stuff, Camellia sinensis, none of that herbal, rooibos or yerba maté bullshit—if we want to significantly lower our blood pressure and risk of diabetes and stroke.

Three to five cups a day?

That's hard to accept, especially in a tea-skeptical (for now) nation like the U.S., where we often eye tea warily as a dehydrating, caffeinated sometimes beverage. After smell-testing the science behind the report, the Council's claims about the leafy brew may be a bit overblown. Yet there's still ample reason to drink much more tea than most of us do. The thing is, "cups per day" recommendations are poor guides given the different chemical profiles of the world's 1,500-plus varieties of tea and in individuals' brewing habits. In fairness to the Dutch, making clear recommendations is difficult. But we can offer some slightly better guidelines.

The Council's claims aren't the boldest ever made. Long trumpeted for its copious antioxidants and as one of the few natural sources of the purportedly calming, attention-boosting amino acid L-theanine (which is lacking in herbal and other teas), a stiff cuppa, according to studies over the past couple decades, may protect against the following litany of maladies: Alzheimer's disease, cancer, food poisoning, high cholesterol, heart attacks, hypertension, influenza, osteoporosis, rheumatoid arthritis, stress, stroke, tooth decay, type 2 diabetes and weight gain. It's also supposed to be hydrating, helpful with gut bacteria, good for immune systems and skin and joints, and boost overall longevity as well.

According to professor Hasan Mukhtar of the University of Wisconsin, the author of a comprehensive review of tea's health effects in humans, most of these claims are weak, if interesting. Yet Mukhtar does believe that two of tea's supposed benefits (its power to ward off some cancers and cardiovascular disease via antioxidant activity) have been proven beyond a shadow of a doubt. So though tea might not be as superpowered as the Health Council of the Netherlands' guidelines suggest, it's still probably good to work into your diet.

Types of tisanes, or herbal teas

Yet a trickle of stories over the past few years have led some to worry about the dangers of overdosing on tea. In 2009, researchers associated a man's tendency to gulp overly hot brews with his esophageal cancer. In 2012, another team correlated drinking more than seven cups of tea a day to a 50 percent spike in a man's likelihood of getting prostate cancer. In 2013, doctors tied an old lady's brittle bones and tooth loss to drinking too much tea. And earlier this year, the media went into a tizzy when doctors linked a girl's hepatitis to drinking three cups of green tea a day.

For all these scary stories though, Mukhtar says there's no evidence of tea itself causing negative effects. Drinking any boiling liquid would lead to esophageal problems. The prostate connection was not causal. The weak-boned lady was suffering from fluorosis, because she was drinking 12 cups of tea a day made with 100 to 150 tea bags, whose packaging contained fluoride. And the hepatitis was likely the result of buying from a poorly regulated internet provider.

For most people, three to five cups a day is safe, unless they have caffeine sensitivities. Unfortunately, we can't be sure that's the right dosage to get tea's known health benefits. We gathered very little data on the ratio of consumption to gain. Even if we did, measuring it in cups would be functionally useless. Each tea has its own concentration of antioxidants and amino acids based on its growing and brewing conditions.

Black teas, which get their color from oxidation, have as low as one-ninth the antioxidants of green tea. The water temperature at which you brew it and the interactions of milk and sugar with a tea may affect its health potential (although we're not sure how). The infinite variability of strength, type and style mean that for some people three to five cups is ideal; other people might need a dozen.

Mukhtar is hesitant to recommend a specific tea or dosage in place of the Dutch guidelines.

"Data is not available yet on which tea is [best]," he says. He will say that most existing data comes from studies on green tea. "So as of now, it definitely looks like green tea has more beneficial effects," he advises. That's an issue, because up to 75 percent of global tea consumption is black. In places like Britain where black tea is losing market share, unproven but well-marketed herbals are taking its place, not tried-and-true greens.

While Mukhtar is hesitant, there are a few things we can say with relative confidence: Loose-leaf teas tend to be higher quality and contain less overdose-risk materials like fluoride. Shade-grown green teas (like high-quality Japanese gyokuros or senchas) have higher levels of L-theanine and lower levels of caffeine than many types of tea. And white teas have especially high levels of antioxidants. Although many guides advise you to stop steeping tea relatively quickly, you usually do better health-wise to steep longer until mild astringency. (Tea's tannic bitterness comes from its antioxidants; its umami savor comes from amino acids.) And though we don't know much about the ideal volumes and concentrations you'd want to consume of these teas, Mukhtar does think three to five cups a day is a good baseline. More probably wouldn't hurt.

"I have no hesitation in recommending that it may do some good," he says. "If it's not going to help you, it's definitely not going to hurt you . . . I think it's a reasonable recommendation."