For years we have been told to beware of caffeine. Now we seem to have swung in the opposite direction, with studies claiming that moderate amounts of coffee may reduce headaches and protect against diabetes, Alzheimer's and heart disease, among others. So where does the truth lie?
We don't all have the same reactions to caffeine, Mehul Dhinoja, a consultant cardiologist at BMI London Independent Hospital, says.
"Each of us has an enzyme in the liver that breaks down and metabolises caffeine. It's that process that enables caffeine to have its effect around the body," he says. "Some people are born with an enzyme that works extremely efficiently and others have quite the opposite. Because this isn't controlled in studies about caffeine, it's not surprising to find statistical contradictions."
Peter Rogers, head of experimental psychology, says some people are more sensitive to the effects of caffeine, while others develop a tolerance. "One of the things caffeine has been found to do is increase blood pressure and make your hands shake a little," he says. "But actually this depends if you're a person who regularly consumes caffeine."
You can even develop a dependence of caffeine so that without it, you can feel fatigued and headachey, he says. "That's why if coffee drinkers haven't had caffeine for a while – for example, overnight – the coffee they have in the morning is likely to make them feel more energetic and alert, while for a non-regular drinker, it will make them jittery."
So while some studies say coffee stimulates the brain and makes drinkers feel more awake, Rogers and his team have found the "caffeine high" may just be a reaction to the body craving the drug. Caffeine may even have radically different effects on the sexes. Studies from Bristol University have found that drinking caffeinated coffee boosted a woman's performance in stressful situations, but had the opposite effect on men, who became less confident and took longer to complete tasks once they had several coffees.
What caffeine is good for
Forget hair of the dog. If you want to cure a hangover, a good old cup of coffee and aspirin really is best, according to a new study from Thomas Jefferson University in Philadelphia. Confirming what many have suspected for years, the research found that the caffeine in coffee and the anti-inflammatory ingredients of aspirin reacted against the chemical compounds of ethanol, or pure alcohol, which – even in small doses – can bring on headaches.
Tim Grattan, who developed the technology for the new paracetamol and caffeine product, Panado Extra Advance, isn't surprised: "There's plenty of clinical evidence that shows caffeine actually speeds up the painkilling properties of various painkillers. In fact, caffeine has played a role in making our new product 37 per cent more tough on pain than ordinary paracetamol tablets."
Drinking lots of coffee can also boost sports performance by as much as 6 per cent – but, critically, only in any activity where muscles are not being worked to the limit, meaning coffee or tea could benefit a long-distance runner but not a sprinter.
Rob James, from the University of Coventry's department of Biomolecular and Sports Science, believes caffeine in the bloodstream may influence receptors on skeletal muscle, making a person temporarily more powerful. If you overdo it, fear not – caffeine can help here, too. A study from the University of Georgia found that caffeine can help reduce the soreness that discourages some people from keeping up their workouts.
What it's bad for
Contrary to popular opinion, one thing coffee doesn't do is sober you up – it may even further impair your judgement, scientists at Temple University in Philadelphia have found. Combining alcohol and caffeine at the same time produces a potentially lethal mix that makes it harder to realise you are drunk, according to the study published in Behavioural Neuroscience. Perhaps less of a surprise is the discovery that energy drinks – some of them, at least – are bad for our health. "There have been increasing instances of atrial fibrillation (AF), a heart-rhythm problem, among young people who consume large amounts of energy drinks," Dhinoja says. It's not just drinks that can cause this problem. In 2009, a 13-year-old boy needed hospital treatment after ingesting "energy" chewing gum that contained 320mg of caffeine – more than in three cups of coffee.
Large amounts of caffeine in pregnancy also appear to be risky. Back in 2008, the Food Standards Agency warned women to have no more than two cups of coffee a day after a study linked caffeine to low birth weight. Caffeine may affect your chances of getting pregnant in the first place, too, according to a Netherlands study that found that women who drank four cups of coffee a day were 26 per cent less likely than average to have conceived naturally.
Caffeine could even shrink some women's breasts. Swedish research found that too much of it can affect hormones, playing havoc with their bust size.
Cancer and heart disease
An analysis of 59 studies just published on the BioMed Central Cancer website suggests that coffee consumption may reduce your overall risk of getting cancer and that it may be inversely associated with the risk of bladder, breast, pharynx, pancreas and prostate cancers and leukaemia, among others. One study even discovered that caffeine can cut the risk of skin cancer by more than a third.
But women who drink more than four cups of coffee a day increase their risk of developing breast cancer by a third, according to Harvard University. A high caffeine intake can also increase the chance of developing larger tumours, which are harder to treat.
The jury is still out on caffeine's relationship with the heart, too. Arthur Klatsky, a cardiologist, and his team at the Kaiser Permanente Division of Research in California discovered that regular coffee drinkers were less likely to be treated in hospital for irregular heartbeats or rhythms. The more cups of coffee they drank each day, the less likely they were to suffer from the condition. Spanish research has even shown that women who drink three cups a day could reduce their risk of dying from heart disease by a quarter, whilst another study found that men who drank five or more cups a day were 44 per cent less likely to die from the disease.
Women who drink tea were recently found by American researchers to be at greater risk of developing rheumatoid arthritis. Other studies have shown tea drinkers can halve their risk of dementia and cut their risk of a stroke. Yet the same cannot be said about coffee drinkers. "This highlights a really important point – that the other constituents in tea and coffee may have their very own impact on health and well-being," Rogers says.
Australian scientists found that drinking three to four cups of coffee a day can lower the risk of type 2 diabetes by 25 per cent, but those who drank decaffeinated coffee showed similar results. And a study of almost 50,000 men found that those who drank the most coffee were 60 per cent less likely to develop the most aggressive form of prostate cancer.
Should we give it up?
Doctors often tell patients to quit caffeine, but that may not be necessary, Rogers says. "It seems to me odd to be telling someone to give up something they enjoy and when there's no real evidence." Rogers followed a group of people with tinnitus – a condition for which caffeine has traditionally been deemed by doctors as a big no-no. "We found that those who did give up caffeine didn't improve their condition in any way." He adds: "Not to undermine the importance of my own research, but tea and coffee are things to worry about so much less than if you're a smoker, overweight or have a poor diet."