The latest research on caffeine reveals why coffee and decaf can be so good for your health, but energy drinks can be lethal
20 August 2024
“I only drink coffee on days ending in y,” so the saying goes. If this mantra applies to you, welcome to the club. Coffee’s best-known component, caffeine, is estimated to be the most widely used psychoactive drug in the world, with billions of people consuming it every day. But unlike other addictive substances, it is largely unregulated, and nobody would flinch at the idea that you might struggle to function without it from the moment you wake up.
Coffee lovers might be on to something, with a slew of studies showing that, taken in the right way, caffeine can improve many things, not least your cognitive abilities and alertness. What’s more, your pursuit of a Java pick-me-up may bring a host of related health benefits. Yet not all sources of caffeine are viewed equally. In recent months, its health risks, especially when in energy drinks, have been in the spotlight again. In June, the UK Labour party, which now forms the country’s government, pledged to ban the sale of these drinks to children under 16 due to their “dangerously high” caffeine content. This comes hot on the heels of a comprehensive report called The Dark Side of Energy Drinks, which documents cases of people who ended up with severe health issues after consuming them.
Dosing is another concern. We don’t all respond to it in the same way – what is safe for you might not be for others. It can be a confusing picture, but unpick the research and you can find ways to use your caffeine cravings to your advantage, without the downsides.
Caffeine is a natural compound found in the seeds, fruits, nuts and leaves of around 60 species of plants, with its bitter taste an evolutionary quirk related to its role as a natural pesticide.
The discovery of its richest natural source, coffee, is said to go back to Ethiopia around AD 850, when a local goat herder noticed his animals getting jumpy after eating berries from an arabica plant. He gave some of the fruits to a local monk, who brewed the world’s first cup of coffee.
We now know this jumpiness boils down to caffeine’s effect on the brain. It only takes around 45 minutes for all the caffeine from a cup of coffee to be absorbed into your circulatory system, where it travels to the brain, easily crossing the blood-brain barrier. Here, it binds to and blocks receptors for the neurotransmitter adenosine. This chemical builds up as the day goes on and dampens nerve fibre activity to make us sleepy. “It slows us down,” says Jennifer Temple at the University at Buffalo in New York. “Caffeine competes with adenosine for access to the receptor, so it has the opposite action – it makes us feel more energetic, alert and awake.”
As anyone faced with a deadline or long drive knows, this has its benefits. Research backs up what coffee drinkers already appreciate: people who downed a shot of caffeine had shorter reaction times and were more alert, focused and cognitively sharp. The effects were physical, too, with better performance in tests of muscle strength, endurance and high-intensity sprints. A recent study of amateur cyclists found that caffeinated coffee improved performance by an average of 1.7 per cent. Such effects tend to last for around 2 hours, although this varies considerably between people and will also be influenced by other factors like the food you ate recently.
The benefits of coffee
Given these findings, it is little wonder that caffeine’s presence in energy drinks in particular is often marketed as a way of focusing attention, improving exam performance and enhancing athletic prowess.
There are other effects, too. After people consume caffeine they tend to report feeling happier, and there are signs that this substance could even cause a longer-term mood boost. For example, studies consistently show that individuals who drink three to four cups (or shots) of caffeinated coffee a day are less likely to experience depression and have a lower risk of suicide. However, the same relationship hasn’t been shown with decaffeinated coffee, suggesting that caffeine itself is responsible.
“The results are quite robust, which is almost surprising because you don’t think of caffeine as being a potent antidepressant,” says Alberto Ascherio at Harvard University.
His work and that of others have also found that drinkers of caffeinated coffee have a significantly lower risk of developing Parkinson’s disease. Although the reason for this is unclear, Ascherio points to caffeine’s known ability to increase levels of the neurotransmitter dopamine in the brain. Dopamine plays a vital role in regulating the movement of the body and a lack of it has been implicated in both Parkinson’s disease and depression.
More good news for coffee drinkers is that consuming it seems to bring a host of benefits that aren’t necessarily anything to do with its most famous component. Purported heart health benefits are a good example, something that, for a long time, wasn’t considered possible with caffeinated coffee at all. “Because there were quite a few reports that caffeine sped up your heart rate and gave some people palpitations, everyone assumed coffee was bad for you,” says Tim Spector at King’s College London.
In a recent study led by Peter Kistler, a cardiologist at the Baker Heart and Diabetes Institute in Melbourne, Australia, more than 380,000 people in the UK were tracked for 10 years to see if they went on to develop cardiovascular disease. People who drank two to three cups of coffee a day generally had a lower risk of developing coronary heart disease, heart failure or arrhythmias, or of dying for any reason during the study period. However, decaf drinkers saw, by and large, the same benefits (with the exception of arrhythmias), suggesting it is something else in coffee that is responsible for its heart-protective effects. “The sweet spot seems to be around three cups of coffee, which is associated with a 25 per cent reduction in heart disease and a reduction in all-cause mortality,” says Spector.
It should be noted that correlation isn’t causation. Most of the studies are epidemiological, which means they involve tracking very large numbers of people over time to see if they go on to develop certain diseases. When it comes to coffee drinking, there are few randomised controlled trials – the gold standard of medical research – because it is very difficult to control for other dietary factors. However, a few such trials have shown that you can reduce biomarkers of heart disease by giving people coffee.
Polyphenols and your microbiome
If caffeine isn’t behind this particular upside of consuming coffee, what is? The answer lies in the drink’s complex nature. Prior to roasting, coffee beans are fermented, which influences the spectrum of biologically active compounds the final drink can contain. These include polyphenols – chemicals made by plants to protect themselves against environmental stresses, such as predation by insects and extreme temperatures – which are thought to have antioxidant and anti-inflammatory effects on the body. Coffee is also high in fibre, a beneficial dietary component that most people don’t get enough of, often associated with a healthy gut microbiome.
Spector believes the gut microbiome may ultimately be behind some of coffee’s positive effects on health. In a study that is yet to be published, he and his team collected stool samples from more than 30,000 people from different countries. They identified a particular bacterium, a type of Lawsonibacter, which is found almost exclusively in the guts of people who drink coffee, including decaf. “You basically have five times the amount of this microbe if you’re a coffee drinker compared to a tea drinker,” says Spector (see “Time for tea“, below). “It’s really interesting because it’s the first time we’ve ever found a microbe that is so fussy. It only eats one type of food. It’s the most specific food-microbe association that’s ever been reported.”
The more coffee you drink, the more your gut will be dominated by Lawsonibacter. This is a good thing, because when these bacteria feed on the fibres and polyphenols in coffee, they release chemicals called short-chain fatty acids that are known to be anti-inflammatory, calming the immune system.
This could explain the reportedly wide-reaching health benefits of coffee. Chronic inflammation is thought to be the main driver of heart disease. Coffee consumption has also been associated with lowered risk of diabetes, obesity and allergies, which are also thought to be aggravated by inflammation, as is depression. “Virtually everything – even mental health – is probably related to low-level inflammation of some kind,” says Spector. “So it’s really important that you have these continuous signals [from the immune system] saying, don’t worry about this, we’ve got it under control. Otherwise, the body thinks it’s under attack.”
Altogether, then, there is robust evidence that caffeine, and more broadly coffee, can be beneficial. “What I would say is that the evidence suggests that if you are a coffee drinker, there is no reason to stop, and that all the data I’ve looked at shows that two to three cups of coffee per day should be considered as part of a healthy diet,” says Kistler.
Other research, however, might kill that buzz. Like many things, especially psychoactive substances, it is possible to have too much of a good thing. Today, we don’t need to rely on natural sources to get our caffeine hit. The stimulant can be synthetically created and added to soft drinks, energy drinks, supplements and even medicines. The concentration of caffeine in these varies hugely and is often equivalent to a cup of coffee, but is sometimes much higher.
Taken in high doses, caffeine causes the adrenal glands to ramp up production of the hormones adrenaline and noradrenaline, activating the body’s fight or flight response. “Your pupils dilate, you start to sweat and your heart rate and blood pressure increase,” says Margaret Thompson at the Ontario Poison Centre in Canada.
It was concerns over “dangerously high” caffeine content that led the UK’s Labour party to pledge to ban energy drinks for children under 16 earlier this year. Now in power, it has proposed legislation to restrict their sale. Energy drinks are particularly popular with young people, with up to half of children worldwide estimated to drink them on a weekly basis. And Temple’s work has found that the combination of caffeine and sugar in them make them especially hard for children to resist, sometimes with risky consequences.
“When people overdose on caffeine, they usually present to emergency departments as agitated, excitable and anxious,” says Thompson. “The agitation can progress so far as to actually cause seizures, and they often complain of palpitations; they feel like their heart is beating abnormally or too fast.”
Caffeine in energy drinks
More problematic still, according to The Dark Side of Energy Drinks, is that these products often contain other legal stimulants, such as guarana, taurine and L-carnitine. Some of these act to further increase blood pressure, heart rate and breathing rate. The case studies in the report make for sobering reading, with examples of people experiencing serious cardiac events after consuming energy drinks.
“While the scientific community is knowledgeable about the pharmacology and effects of caffeine, much less is known about the interactions among all the ingredients and their long-term effects related to chronic consumption,” says Andrea Costantino, a doctor now at the Careggi Hospital in Florence, who co-authored the report.
To make matters worse, sensitivity to caffeine varies wildly. Some people can guzzle three cans of energy drink in quick succession with little effect, while others aren’t so lucky. This is at least in part due to the fact that there are many variants of the adenosine receptor across the human population, says Temple. Once people become habituated to caffeine, they also need more of it to get the same buzz.
Perhaps unsurprisingly, children who drink caffeine, particularly later in the day, take longer to fall asleep at night, sleep for less time and have poorer-quality sleep overall than children who don’t drink caffeine.
The clear message, then, is that energy drinks – and to a lesser extent fizzy caffeinated beverages – can be bad for your health. “Energy drinks are ultra-processed and full of sugar, artificial sweeteners, artificial flavourings and all kinds of other preservatives and chemicals. So they have nothing good to offer at all,” says Spector. If you must drink them, as a rule of thumb Costantino recommends that adults stick to one can at a time, with a maximum of two per day to remain within an acceptable safety limit.
As for coffee, the chief source of caffeine for many people, the findings suggest that most of us could benefit from drinking around three cups a day. While there are fewer long-term studies of decaf, the few there are show it may be just as effective at warding off heart disease and diabetes. However, if you want to lower your risk of depression and Parkinson’s, then go for the real deal.
That is, of course, unless you are one of those people who are particularly sensitive to caffeine. “I know people who, after a couple of sips of something with caffeine in it, feel awful. They’re jittery, anxious, and their heart rate rises,” says Temple.
Pretty much everyone else can enjoy their coffee hit guilt-free, any day of the week.
Time for tea
Tea has long been considered a healthy drink, with proponents claiming it could boost your immune system, dampen inflammation and even ward off cancer and heart disease. But does the evidence stack up? Where better to find out than in the UK, renowned as a nation of tea lovers?
One recent study tracked 500,000 tea drinkers there over 11 years. It showed that drinking two to three cups of black tea a day was associated with a modest 9 to 13 per cent lower risk of death. Higher tea consumption was also associated with a lower risk of death from cardiovascular disease, ischaemic heart disease and stroke.
However, green tea, which is made from unfermented leaves, may be even better. It is richer in polyphenols, which act as powerful antioxidants. These disarm and neutralise reactive chemicals known as free radicals, which destroy cells and DNA.
“Based on the current evidence, black tea – which most English people drink – is not as healthy as coffee and doesn’t have the same benefits, particularly on the heart,” says Tim Spector at King’s College London. But if coffee (see main story) isn’t your, ahem, cup of tea, you might want to consider green tea instead to reap similar health benefits.