Think green tea is good for your brain and heart? Chamomile will help you sleep? Dandelion supports liver health? Elderberry wards off colds? Some teas, it turns out, do a lot more for you than just tasting good.
But while some of the purported benefits of popular infusions are backed by solid evidence from well-designed randomized controlled studies, others are based on the results of a single small trial of 17 people, and some teas have been the subject of rigorous studies that failed to demonstrate any health-promoting activity.
Here, we break down what the research does and doesn’t tell us about 24 commonly consumed teas.
Six of the teas on this list are actually made from the same plant (Camellia sinensis), and they’re just processed differently: black, green, white, oolong, matcha and pu-erh. They all have similar compounds like caffeine, the amino acid theanine and antioxidants known as catechins (a type of polyphenol). The remaining 18 aren’t teas at all, as they’re actually herbal infusions, which are made from everything from flowers to fruits to bark to roots, and are usually caffeine-free. And while they all technically go by the word “tea,” they’re much different from one another.
How the Grades Work
Strong means meta-analyses of randomized controlled trials, or multiple high-quality randomized trials, have shown a significant effect in humans. Moderate means at least one high-quality randomized trial (often small in size and rarely replicated at this stage) has shown a significant effect in humans. Early means there is at least one pilot study, non-controlled clinical trial or small randomized trial showing promise, although the effect may have waned after a few weeks. Weak means clinical trials in humans have shown no significant effect, or evidence is currently limited to in-vitro (test tube) or animal studies. Each card also says what form was tested (extract or infusion), as this is where a lot of confusion creeps in, since a 1,200 mg tulsi extract is not the same thing as drinking a cup of tulsi (holy basil) tea, nor is peppermint tea equivalent to peppermint oil capsules.
The Six True Teas
Of the 24 beverages, green tea has the strongest research base for possible health benefits. In a prospective study of 40,530 Japanese men and women followed for up to 11 years (the Ohsaki Study), women who drank five or more cups of green tea a day had a 23 percent lower risk of death from any cause and a 31 percent lower risk of dying from cardiovascular disease than women who drank less than one cup a day. For men, heavy green tea consumption was associated with a 12 percent lower risk of death from any cause. In a meta-analysis of 14 randomized trials (1,136 participants), green tea decreased total cholesterol an average of about 7 mg/dL and LDL cholesterol about 2 mg/dL but didn’t affect HDL cholesterol. In a meta-analysis of 25 trials, drinking green tea for 12 weeks or longer decreased systolic blood pressure an average of about 2 mmHg.
In a cross-sectional study of 1,003 Japanese adults older than 70, those who drank two or more cups of green tea a day had about half the odds of cognitive impairment compared with those who drank less than one cup a day. However, because this was a cross-sectional study, it can’t tease apart whether it was the green tea or something else about the people who drink green tea that reduced their risk of cognitive problems.
Drinking actual matcha, that is, whisking matcha powder into hot water so you consume the whole ground-up green tea leaf instead of merely infusing green tea leaves in hot water, has been studied in only two small randomized trials. In one trial, consuming 4 grams of matcha improved some aspects of attention (basic attention and psychomotor speed, but not memory) and did not alter mood one hour later in 23 adults. In the other trial, consuming 2 grams per day of matcha for two weeks improved the ability to sustain attention after a stressful task compared with placebo in 42 adults aged 25 to 34 years. These are promising but small studies and matcha’s effects in them were fairly modest. More research is needed before we can say definitively whether or not matcha boosts attention, but given that matcha is a form of green tea, any effects it does have are likely to be similar to those of other green teas owing to the presence of theanine and caffeine.
When it comes to types of tea and lowering blood pressure, black tea seems to get the most research attention. In a meta-analysis that looked at 25 trials, black tea consumed for at least 12 weeks significantly reduced systolic blood pressure (by about 1.4 mmHg) and diastolic blood pressure (by about 1.1 mmHg). While these may seem like small decreases for the individual, on a population level they can make a big difference.
As for that buzz you’re after, according to a review of studies looking at the acute effects of tea consumption, the most consistent results were improvements in attention and alertness (as rated by the participants themselves) for up to an hour. And while black tea does contain the brain-boosting amino acid theanine, it’s also got about 47 milligrams of caffeine per 8-ounce, brewed cup, according to the USDA. (Compare that to coffee’s average of about 95 milligrams per cup.)
In one tiny study using a room calorimeter, 12 men burned 2.9 percent more calories in 24 hours when they drank oolong tea instead of water.
They also burned 12 percent more fat. But that was full-strength oolong tea. And when they drank water with the same amount of caffeine, they burned almost exactly the same amount of extra calories. So, it’s probably the caffeine.
Anyway, we’re talking about 67 calories here. Not exactly diet tea.
White tea’s anti-aging reputation comes from the lab bench. In a lab screen of 21 plant extracts for collagenase and elastase inhibition, white tea was the clear winner at some 89 and 87 percent inhibition of these collagen/elastin (skin protein) breaking down enzymes, respectively. These are test-tube studies though; no human studies have been conducted to determine if drinking white tea will slow aging of skin.
Pu-erh (also spelled pu’er) is an aged, fermented tea that has a longstanding reputation as a cholesterol-lowering therapy. Human research on pu-erh’s cholesterol-lowering effect is limited to a single, 12-week study among 36 overweight Japanese men and women, in which a pu-erh extract taken in water form before meals helped them lose belly fat, as measured by CT scans, and showed a modest decrease in BMI and waist size compared with a placebo. Blood lipids didn’t change significantly. In 2019, a study published in Nature Communications showed that, mostly in mice, pu-erh tea reduced cholesterol through an action on bile acids and gut bacteria.
The Calming and Sleep Teas
Chamomile might be the most-researched sleep-promoting tea. A 2019 meta-analysis that looked at the results of 12 randomized controlled trials concluded that chamomile significantly improved sleep quality, and also had a modest effect on generalized anxiety disorder (but not on state anxiety, which refers to everyday feelings of anxiety). However, it’s worth noting that the only trial included in the meta-analysis that specifically studied people with insomnia found no significant benefit from chamomile, and the anxiety trials used a standardized extract in capsule form, not chamomile tea. One of the trials in the meta-analysis, however, did use chamomile tea: in this study of 80 postpartum women in Taiwan, those who drank chamomile tea for two weeks had fewer sleep-related physical symptoms and lower depression scores at the end of the study compared to the control group, but these differences weren’t significant two weeks after the intervention ended.
In an 8-week placebo-controlled trial of 80 patients with stable angina, taking 3 grams of lemon balm per day reduced depression, anxiety, stress and sleep-disturbance scores compared with placebo.
Lemon balm may promote relaxation and calmness. In a placebo-controlled crossover trial of 18 healthy volunteers, 600 milligrams of lemon balm extract promoted feelings of calmness during a stress-inducing laboratory task. Note that none of these studies used brewed lemon balm tea.
Lemon balm may help you fall asleep. In a small open-label pilot study of 20 volunteers, taking lemon balm extract significantly reduced insomnia (sleeplessness) symptoms by 42 percent. However, without a control group receiving placebo, these results should be interpreted with caution. Again, this study did not use brewed lemon balm tea.
Valerian root extract is often touted as a powerful natural sleep aid but that powerful may be a stretch. A 2006 meta-analysis of 16 studies (1,093 participants) did find that those who took valerian were 1.8 times more likely to report improvements in sleep quality compared with those who did not take valerian. However, many of the studies included in the meta-analysis had methodological problems and there was evidence of publication bias. Another review published in 2020 that analyzed 60 studies concluded that the varying efficacy results seen in valerian studies could be explained by the inconsistent quality of valerian extracts with whole-root preparations most likely to be effective. Overall, it appears that valerian root extract is sometimes helpful for promoting sleep and is generally well-tolerated.
There have been a few studies done on the effect passionflower has on the quality of sleep. In one such study 41 healthy volunteers were given passionflower tea and a placebo tea (in a randomized order) to drink once a day for one week each. The volunteers were asked to keep a sleep diary and there was a statistically significant improvement in sleep quality during the week they drank passionflower tea. A smaller subset of these volunteers also had their sleep assessed in a sleep laboratory but this group was too small to demonstrate any significant effects. For anxiety, passionflower extract given as drops (not tea) was found to be as effective as the benzodiazepine oxazepam (but with less impairment of work performance) in a four week study in 36 outpatients suffering from generalized anxiety disorder.
One trial included 80 postpartum Taiwanese women experiencing sleep disturbances who were given lavender tea to sip and smell every day for 2 weeks and found significant reductions in depression and fatigue levels compared to a control group receiving usual care. However, these effects did not persist when the women were re-evaluated two weeks after the end of the trial. Another study looking at the effect of different aromas on cognition found that lavender impaired reaction times and working memory. The stronger lavender evidence is for oral lavender oil capsules and for aromatherapy, not for tea.
Another herb touted as an adaptogen is tulsi (holy basil). In a 2017 systematic review, researchers found 24 studies conducted in humans that showed tulsi’s potential to help with blood sugar control, immunity and stress with no reports of serious adverse events. However, the researchers noted that more research is needed and most of the studies were small. In one of the better studies looking at tulsi’s effects on stress, 71 people took 1,200 milligrams of a standardized tulsi extract daily for six weeks. Those who took tulsi had improvements in stress symptoms that were 39 percent greater than those who took a placebo. Keep in mind that that’s quite a bit more tulsi than you’re likely to get from steeping a tea bag.
The Digestion Teas
Peppermint might be one of the best-studied teas, and there’s good evidence to back up its reputation. For bloating after a meal, a cup is a reasonable thing to try. But if you have irritable bowel syndrome and are looking for relief, it’s probably worth going with enteric-coated peppermint oil capsules rather than tea. That’s because one 2019 meta-analysis that included 12 studies and a total of 835 IBS patients showed that peppermint oil more than doubled a person’s chances of experiencing an improvement in IBS symptoms overall (with a number needed to treat of three). Those were all randomized controlled trials using enteric-coated peppermint oil capsules, which get through the stomach and release highly concentrated menthol (the active ingredient in peppermint oil) in the intestines. Tea bags release much less of the active ingredient, and it’s released in the stomach, where it can actually worsen heartburn by relaxing the valve at the top of the stomach.
Peppermint oil can be used topically, too. It may ease headaches when applied to the temples.
For nausea during pregnancy, a meta-analysis of 12 randomized trials (totaling 1,278 women) found ginger to be superior to placebo for improving nausea (but not vomiting) with no increase in adverse effects (miscarriage, heartburn, drowsiness). Lower doses (under 1,500 milligrams a day) may be most effective. For osteoarthritis pain, a meta-analysis of five studies (totaling 593 people) reported a small significant benefit of ginger on pain and disability scores. However, study dropouts due to side effects were more than doubled with ginger. A strong ginger tea (made with about a tablespoon of fresh grated ginger) would approximate the doses used in these studies.
Licorice root may help calm a sore throat, as at least one study, done in an operating room, found that 40 surgical patients who gargled with a solution of half a gram of licorice in water before intubation (insertion of a breathing tube) experienced less sore throat and coughing after their surgeries than those who gargled with just water.
Licorice may also be helpful for heartburn and other symptoms of acid reflux as well as indigestion. In one 30-day study, functional dyspepsia (indigestion) symptoms improved significantly in those taking 75 milligrams twice daily of a deglycyrrhizinated licorice extract compared to those taking a placebo.
However, glycyrrhizin (the part of licorice that’s removed in deglycyrrhizinated licorice) can raise blood pressure and lower potassium levels when taken regularly. Because of this effect, licorice tea is better saved for special occasions and should be avoided by anyone with high blood pressure or taking medications to control blood pressure.
It’s often touted as a liver detoxifier, but there’s no evidence of dandelion’s effectiveness for this use in humans. (Besides, there’s no such thing as detoxifying the liver.)
One small pilot study looked at dandelion leaf’s effect on urine production. Seventeen study volunteers took fresh dandelion leaf extract three times a day and recorded their urine output. Relative to fluid intake, urine output increased after the second dose, and participants reported needing to urinate more frequently during the five hours following the first dose. There was no effect on urine production after the third dose. Though there was no control group in this study, results suggest dandelion leaf has a diuretic effect, but one that’s fairly weak and short-lived.
The Heart and Blood Pressure Teas
Hibiscus tea was shown in a six-week, randomized study of 65 people with prehypertension or stage one hypertension that drinking three 8-ounce cups a day of hibiscus tea lowered systolic blood pressure an average of 7.2 mmHg compared to 1.3 mmHg in those drinking a placebo beverage. The greatest drops were seen in those whose systolic blood pressure started out highest. The infographic calls hibiscus rich in vitamins, but it’s probably the anthocyanins and organic acids that are responsible for hibiscus tea’s effect on blood pressure. According to a 2015 meta-analysis of five studies involving 390 people, hibiscus tea can lower systolic blood pressure an average of 7.6 mmHg and diastolic blood pressure an average of 3.5 mmHg, which is three to five times the effect of either black or green tea. Anyone on blood pressure medication should know that hibiscus adds to it.
One small study on rooibos, the caffeine-free red bush tea from South Africa, found some heart-related improvements, but more research is needed to confirm benefits.
In one trial, 40 people at risk for heart disease drank six cups of rooibos tea daily for six weeks. LDL (bad) cholesterol levels dropped (from 178 mg/dL to 151 mg/dL), as did triglycerides, and HDL (good) cholesterol went up. Blood markers of lipid oxidation also decreased.
While these results are interesting, the study didn’t have a placebo group, and six cups of rooibos tea a day is quite a bit. So while the tea may offer some heart benefits, more research is needed to confirm any health advantages.
The Immune and Allergy Teas
Of the 24 we looked at, elderberry had the most conflicting body of evidence. In one randomized trial involving 312 long-haul air travelers, those who took a standardized elderberry extract experienced significantly shorter colds (57 vs. 117 sick days), and lower symptom scores, although no significant difference in the number of colds. In a 2019 meta-analysis involving 180 participants, elderberry significantly and substantially reduced upper respiratory symptoms. But in a 2020 study conducted in emergency rooms involving 87 patients with lab-confirmed influenza, elderberry extract had no effect on duration or severity of the flu; in a post hoc analysis, flu patients taking elderberry extract (alone) actually fared two days worse than placebo. These studies used elderberry extract or syrup, not tea. Also, elderberries, as well as the plant’s stems and leaves, contain compounds that can release cyanide, so the berries need to be cooked.
The 2014 Cochrane review looked at echinacea for the common cold. The review included 24 double-blind studies involving a total of 4,631 people. Overall, the studies didn’t show echinacea to be effective for treating colds (only one of seven studies found echinacea shortened the duration of colds). There may be a modest effect (10 to 20 percent relative risk reduction) in preventing colds, according to pooled results from the studies; however, none of the 12 prevention comparisons against placebo found a statistically significant decrease in the number of people who developed colds. The authors of the Cochrane review concluded that echinacea products have not been shown to help treat the common cold, but some products may have a weak preventive effect. One study evaluated echinacea tea. People who were starting to feel cold symptoms and drank five to six cups of echinacea tea per day for as long as they had symptoms thought their symptoms lasted less time than did symptoms in people who drank a placebo beverage. However, this 95-person study relied on a single questionnaire completed two weeks after cold-like symptoms began.
A 2018 systematic review of 10 studies looking at the effects of Asian and American ginseng on fatigue found modest evidence that ginseng may be helpful, particularly for people with chronic illnesses. The risk of adverse events was considered to be low. Most of the studies examined used standardized capsules of ginseng.
A 4-month-long randomized trial involving 323 adults living in Canada found that taking a standardized extract of American ginseng reduced the average number of colds contracted (from 0.93 to 0.68 colds per person) and significantly decreased the likelihood of getting more than one cold (from 22.8 to 10 percent).
Note that little ginseng root is added to most commercially available ginseng teas, and the amount of ginseng added is rarely listed.
Nettle is not an antihistamine.
The evidence does not support using nettle for seasonal allergies. In a small 98-person trial of patients with allergic rhinitis, freeze-dried nettle was rated superior to placebo on a global assessment in 1990, but only marginally superior on diaries of daily symptoms. In a 2017 double-blind trial of 74 patients, nettle and placebo were equally effective at improving symptoms (both improved significantly).
Nettle tea is tasty and full of minerals, just not antihistamines.
The Brain and Joint Teas
One study looked at memory in 144 adults who performed tasks while sitting in a cubicle that smelled of rosemary, lavender or nothing at all. Those in the rosemary-scented cubicle did better on measures of the quality of their memories but worse on measures of the speed of their memories. Another study, a crossover trial in which 28 people, average age 75, received either dried rosemary leaf powder or placebo, found that the lowest dose of rosemary studied (750 milligrams of dried leaf, about what you might use in cooking) improved the speed of memory and the highest dose (6 grams of dried leaf) impaired it. So if you want the potential benefit of rosemary on memory, it may be important not to have too much. A cup of rosemary tea, for example, would probably be on the low side.
Turmeric’s anti-inflammatory action is real in research studies and dubious in a teacup.
Several clinical studies have investigated the effects of turmeric and curcumin on inflammatory conditions. A meta-analysis of eight randomized trials concluded that turmeric extracts and curcumin had significant anti-inflammatory effects and produced improvements in arthritis pain and stiffness scores when compared with placebo. In trials that directly compared curcumin with standard anti-arthritis medications, curcumin worked just as well as the medications in easing arthritis pain and stiffness. Most of the studies used doses providing approximately 1,000 milligrams of curcumin per day.
Unfortunately, curcumin is not well absorbed, is rapidly metabolized by the body, and has very low solubility in water. Most of the clinical studies have used well-standardized curcumin or turmeric extracts (often in combination with piperine, a component of black pepper, which enhances absorption of curcumin). Because ground turmeric root contains only a few percent curcumin, a cup of tea made with a teaspoon of ground turmeric root provides only a fraction of the curcumin used in these studies, and much of that won’t be well-absorbed.
Turmeric tea may provide some anti-inflammatory benefits, especially if you add some fat (such as milk) and black pepper to your tea. If you’re looking for significant anti-inflammatory benefits, though, a curcumin supplement in capsule form may be more effective.
Pooled randomized trials or several strong human trials.
At least one well-run randomized human trial.
A pilot, small trial, uncontrolled study or short-lived effect.
Negative human trials or evidence limited to laboratory or animal studies.
Caffeine, for the Record
Caffeine content varies widely. According to the USDA, an 8-ounce cup of brewed black tea has on average about 47 milligrams of caffeine, oolong about 38 and green about 28; brewed coffee averages about 95 milligrams. (Matcha is generally higher in caffeine than other green teas because instead of just steeping the leaf, you’re consuming the whole thing.) Of the teas discussed here, only the six true teas contain caffeine, and every one of them has less than coffee.
All of the herbal teas are naturally caffeine-free, which is one of the reasons why chamomile, lemon balm and passionflower are the ones to sip before bed and the true teas aren’t.
What 24 Teas Add Up To
That’s where the grades get interesting: The best-studied teas, those with the most compelling evidence, are the ones we’ve been sipping on for centuries and researching for decades: green, black, hibiscus, chamomile, ginger and peppermint. Some of the flashier teas and their purported powers, say, dandelion to cleanse, white tea to stave off aging, echinacea and nettle to protect, are backed by a pilot study, lab research or even studies that didn’t find any effect. And it turns out that for a slew of surprising teas, including valerian, turmeric, tulsi and ginseng, studies have investigated the herb, but not the herbal tea, because the subjects took supplements in capsule form.
But none of that takes away from the cup. Before you tally the polyphenols, swapping an unsweetened, calorie-free cup of tea for soda is a no-brainer win.
Teas that can interact with meds, especially if consumed on a daily basis for medicinal reasons, include licorice, hibiscus and valerian, among others, so it’s worth a chat with your doctor or pharmacist. And remember that different types of tea have different benefits, with hibiscus to help lower high blood pressure, chamomile or passionflower to help you unwind at night, ginger to help quell nausea, and black or green tea to sip on throughout the day.
Martha ‘Marti’ Jones founded Fitness Four after three decades of living with IBS, Hashimoto’s thyroiditis, and pernicious anemia.
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