Countless arguments have been waged over the superiority of one beverage over the other. But what does the scientific evidence say?

George Orwell may have written that “tea is one of the mainstays of civilization in this country” – but even we British have to acknowledge that our national drink is facing stiff competition from the espressos, cappuccinos, and lattes invading our shores.

Despite the dangers of wading into such a charged argument, BBC Future decided to weigh up the relative merits of each drink. There’s no accounting for taste, of course, but we have combed the scientific literature for their real, measurable effects on our body and mind.

The wake-up call
For many, the caffeine kick is the primary reason we choose either beverage; it’s the oil to our engines when we’re still feeling a bit creaky in the morning. Based purely on its composition, coffee should win hands down: a cup of tea has about half the dose (40 milligrams) of the stimulant caffeine that you would find in a standard cup of brewed filter coffee (80 to 115 milligrams). Yet this doesn’t necessarily reflect the jolt of the wake-up call.

Caffeine dose is not the whole story: perhaps our expectations also determine how alert we feel

Dosing subjects with either tea or coffee, one (admittedly small) study found that both beverages left subjects feeling similarly alert later in the morning. Although that study was based on self-reported feelings of alertness, clear differences have failed to emerge in more objective measures of concentration, either – such as reaction times. Indeed, when you dose up on tea made to the equivalent strength as coffee, it actually proves to be more effective at sharpening the mind.

The scientists conclude that the caffeine dose is not the whole story: perhaps our expectations also determine how alert we feel, or it could be that it’s the overall experience of the tastes, and smells, of our favourite drink that awakens our senses.

Verdict: Against logic, tea seems to provide just as powerful a wake-up call as coffee. It’s a draw.

Sleep quality
The biggest differences between coffee and tea may emerge once your head hits the pillow.

Comparing people drinking the same volume of tea or coffee over a single day, researchers at the University of Surrey in the UK confirmed that although both drinks lend similar benefits to your attention during the day, coffee drinkers tend to find it harder to drop off at night – perhaps because the higher caffeine content finally catches up with you.

Tea drinkers, in contrast, had longer and more restful slumbers.

Verdict: Tea offers many of the benefits of coffee, without the sleepless nights – a clear win.

Tooth staining
Along with red wine, coffee and tea are both known to turn our pearly whites a murky yellow and brown. But which is worse?

Most dentists seem to agree that tea’s natural pigments are more likely to adhere to dental enamel than coffee’s – particularly if you use a mouthwash containing the common antiseptic chlorhexidine, which seems to attract and bind to the microscopic particles.

Verdict: If you want a perfect smile, coffee may be the lesser of two evils.

A balm for troubled souls…
In England, it’s common to give “tea and sympathy” to a distressed friend – the idea being that a cup of Earl Grey is medicine for troubled minds. In fact, there is some evidence that tea can soothe your nerves: regular tea drinkers do tend to show a calmer physiological response to unsettling situations (such as public speaking), compared to people drinking herbal infusions. Overall, people who drink three cups a day appear to have a 37% lower risk of depression than those who do not drink tea.

There is some evidence that tea can soothe your nerves

Coffee doesn’t have the same reputation; indeed, some report that it makes them feel like their nerves are jangling. Yet there is some evidence that it too may protect against long-term mental health problems. A recent “meta-analysis” (summarising the results of studies involving more than 300,000 participants) found that each cup of coffee a day seems to reduce your risk of developing depression by around 8%. In contrast, other beverages (such as sweetened soft drinks) only increase your risk of developing mental health problems.

We need to take such results with a pinch of salt: despite the scientists’ best efforts, in this kind of large epidemiological study it’s hard to rule out other factors that may be behind the link – but it could be that both drinks offer a cocktail of nutrients that dampen down stress responses and boost mood in the long-term.

Verdict: Based on this limited evidence, it’s a draw.

…and a balm for bodies
Similarly tantalising, though preliminary, epidemiological studies have suggested that both coffee and tea offer many other health-giving benefits. A few cups of either beverage a day appears to reduce your risk of diabetes, for instance. (The exact size of the benefit is still under discussion – estimates vary from around 5 to 40%.) Since even decaf coffee confers the same benefits, it seems likely that other nutrients may be oiling the metabolism so that it can still efficiently process blood glucose without becoming insensitive to insulin – the cause of diabetes.

A few cups of either beverage a day appears to reduce your risk of diabetes

Both drinks also seem to moderately protect the heart, although the evidence seems to be slightly stronger for coffee, while tea also appears to be slightly protective against developing a range of cancers – perhaps because of its antioxidants.

Verdict: Another draw – both drinks are a surprising, health-giving elixir.

Overall verdict: Much as we Brits would have liked tea to come out the clear victor, we have to admit there is little between the two drinks besides personal taste. Based solely on the fact that it allows you to get a better night’s sleep, we declare tea the winner – but why not share your own thoughts with us through social media?

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David Robson is BBC Future’s feature writer. He is @d_a_robson on Twitter.

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