London – Not a week goes by, it seems, without another study showing the health benefits – or risks – of coffee.
Just recently coffee was linked to a reduced risk of heart attacks. It’s been shown to protect against dementia, type 2 diabetes and even skin cancer. But it’s also been blamed for anxiety, heartburn and making menopausal hot flushes worse.
All these effects, good and bad, are largely down to the caffeine found naturally in coffee beans.
However, coffee also contains a range of antioxidants and plant chemicals that give the drink its characteristic smoky bitterness and smell, as well as healthy properties.
So how much coffee can you drink to reap the benefits and not suffer the risks?
‘In moderation, up to three cups a day, coffee is probably health neutral or may even have health benefits,’ says dietitian Nigel Denby.
Here, we reveal how your daily cup affects your body – and when you should avoid it…
Choose your coffee wisely and it could help you lose weight. Swapping that caffe latte, which provides around 170 calories if made with whole milk, for black coffee will save you around 160 calories in one drink.
But coffee may help more directly. ‘As well as being practically calorie-free, coffee may be a mild appetite suppressant,’ says Nigel Denby.
And a recent study found that green coffee, made from unroasted coffee beans, may aid weight loss by reducing the amount of sugar absorbed from the gut, and speeding up the rate at which the body burns fat. This is down to chlorogenic acid, a compound in coffee.
Just one cup of coffee can raise the heart rate to 100 beats per minute (normally it’s between 60 and 80) and it can take up to an hour to get back to normal. It can also cause the arteries to constrict, which tends to raise blood pressure, explains Dr Graham Jackson, a consultant cardiologist at Guy’s and St Thomas’ NHS Foundation Trust.
For a healthy person, this will not cause ill effects, and may even give you an energy boost. Furthermore, a moderate consumption may also ward off heart attacks.
Writing in the journal Heart, scientists in South Korea found that men and women who drank moderate amounts of coffee were less likely to have high levels of calcium in their arteries – an early indicator of blocked arteries – though it’s not clear why.
However, for people with heart failure – where the heart is damaged and not pumping blood effectively – coffee may put their heart under greater strain. Dr Jackson advises they consider giving up coffee altogether.
And people with heart disease should avoid instant coffee because it contains high levels of potassium, which can cause dangerous changes in heart rhythm, says Dr Jackson.
That first cup of the day can trigger a need for the loo. That’s because caffeine stimulates and increases the contractions in the bowel, which pushes out waste faster than normal.
This also means that nutrients have less time to be absorbed as they pass through the digestive tract, which could be harmful if you’re not eating a healthy balanced diet. Caffeine also interferes with the absorption of iron, so avoid having it at the same time as iron-rich food, such as red meat.
Contrary to common belief, coffee does not ease constipation. Although it may cause temporary spasms and urgency feelings, it won’t cure any underlying problems. In fact, in the long term coffee can make constipation worse because caffeine can lead to dehydration, resulting in hard stools that are more difficult to pass.
And avoid drinking coffee without food. Caffeine stimulates the production of gastric juices in the stomach – even if there’s no food to be digested. ‘If you drink coffee on its own, the gastric acids can irritate the lining of the stomach and intestine, leading to pain and bloating,’ says Iain Jourdan, a colorectal and general consultant surgeon at the Royal Surrey County Hospital, Guildford.‘The best thing to do is always drink coffee at the same time as eating something.’
Too much coffee could raise your risk of crumbly bones or osteoporosis, because it may speed up bone loss.
Caffeine makes the osteoblasts – the cells involved in forming new bone – less efficient and may even kill them, according to a study published in the Journal of Orthopaedic Surgery and Research in 2006.
‘Caffeine also affects absorption of calcium from the gut and accelerates calcium excretion, potentially leading to bone loss,’ says Julia Thomson, a specialist nurse at the National Osteoporosis Society. Calcium is essential for strong bones.
She advises no more than three cups a day and adding milk. ‘Studies show milky coffee could help to counteract the calcium-leaching properties of caffeine.’
Worried your morning espresso stains your teeth? Surprisingly, tea may be worse.
‘Tannin in tea is a much more powerful staining agent than caffeine,’ says Dr Mervyn Druian, dentist and partner at the London Tooth Whitening Centre. ‘You have to drink quite a lot of black coffee to stain your teeth – five to six cups a day,’ he says. ‘White coffee will also stain teeth but is less concentrated, so the effect is less.’
He says staining from coffee is very superficial, affecting just the biofilm, a thin layer of bacteria which covers the teeth and gums, and doesn’t penetrate through the enamel itself.
A good whitening toothpaste can remove up to 90 percent of stains within 14 days, he says. If enamel is cracked or damaged, you might need professional help.
In more good news for aficionados, Dr Druian says that coffee - including decaf - contains a chemical which effectively stops the tooth-eating bacterium Streptococcus mutans attaching to your teeth. The same chemical is what gives coffee its sweet, earthy taste.
‘Coffee breath’ is a term for particularly noxious bad breath associated with heavy coffee drinking. It’s actually caused by the coffee drying out your mouth, says Dr Druian.
‘Coffee is dehydrating and people who drink lots of it tend to have drier mouths,’ he says. As a result, the mucosal cells that line the inside of the mouth, which live for just three days, aren’t flushed away after they die.
‘Instead, they hang around and start to decay, releasing sulphurous gases,’ says Dr Druian.
A simple solution is to restrict coffee drinking and eat little and often to stimulate production of saliva. Drinking water with coffee can also help. ‘Chewing sugar-free gum after coffee has the same effect, without too many calories,’ Dr Druian adds.
Moderate coffee consumption may lower the risk of Alzheimer’s disease by up to 20 percent, according to a recent study by the Institute for Scientific Information on Coffee.
The study found people who drank three to five cups a day were 20 percent less likely to develop this form of dementia. It seems caffeine helps prevent the formation of the plaques and protein ‘tangles’ in the brain that have been linked to Alzheimer’s.
It also seems that both caffeine and the antioxidants in coffee reduce inflammation in the brain and can slow down the deterioration of brain cells, especially those found in the areas of the brain associated with memory.
The majority of studies suggest regular coffee consumption over a lifetime ‘is associated with a reduced risk of developing Alzheimer’s disease, with an optimum protective effect occurring with three to five cups of coffee per day’, said Dr Arfan Ikram, an assistant professor in neuroepidemiology at Erasmus Medical Centre Rotterdam, who headed up the study.
COffee is a diuretic - it stimulates the kidneys to excrete more fluid, making you need the loo more often. This is because caffeine interferes with the way fluid is reabsorbed into the blood, says Professor Chris Eden, a consultant urologist at the Royal Surrey County Hospital in Guildford.
‘This is not necessarily a bad thing if you have normal kidney function, but studies show that long-term consumption of coffee can make kidney disease worse.’
Caffeine is also a bladder irritant, which can make an overactive bladder problem worse, he says.
Coffee is rich in oxalates, compounds that bind with calcium in the blood to create calcium oxalate, a major component of kidney stones. People with a history of kidney stones had increased levels of calcium in their urine after drinking two cups of coffee each day, according to a U.S. study in 2004. ‘Coffee is health neutral for people who are healthy, but needs to be treated with caution if you have health issues,’ says Professor Eden.
While coffee has a dehydrating effect on the body, it won’t dry out the skin, says Dr Nick Lowe, a leading dermatologist based in London. ‘You have to be exremely dehydrated for the skin to start showing the effects, which is rare if you stick to drinking three to four cups of coffee each day.’
And coffee may be linked to a lower risk of skin cancer, thanks to its antioxidants. These are thought to mop up free radicals, the damaging molecules linked to cancer and other diseases.
A study published in 2005 found that people who drank the most coffee were least likely to get malignant melanoma.
TYPE 2 DIABETES
There are plenty of studies suggesting that drinking plenty of coffee is linked to a lower risk of type 2 diabetes. Recent U.S. research involving 123,000 people found that those who drank three to five cups of coffee a day were less at risk of the disease.
It’s not clear why coffee might help. But as Dr Frank Hu, professor of nutrition and epidemiology at the Harvard School of Public Health, who led this research, explains: ‘The current thinking is that it is the combination of antioxidants and other nutrients in coffee.’
Drinking coffee could give your muscles a boost and provide more staying power. Researchers at the Australian Institute of Sport found that a single cup of coffee helped athletes exercise for almost a third longer.
Cyclists were either given water to drink as they pedalled, or coffee or cola, which also contains caffeine. Those who drank coffee or cola were able to go on for longer.
Caffeine appears to trigger the muscles to start burning up fat for energy once the energy from carbs has run out. Caffeine is also known to help open up the airways - it’s chemically similar to the drug theophylline, which is used to treat asthma.
IT CAN MAKE YOU MORE TIRED
COFFEE is a very effective ‘pick-me-up’. Caffeine triggers the body’s ‘fight or flight’ response, raising your blood pressure and heart rate to give you a burst of energy, says Steve Bazire, professor of pharmacy practice at the University of East Anglia. Caffeine also stimulates the release of feel-good hormone dopamine, temporarily reducing fatigue.
And it works quickly - caffeine is absorbed quicker in liquid form, says dietitian Nigel Denby. ‘It reaches its highest concentration in the bloodstream and in the brain within 30 to 40 minutes.’
It takes around three to six hours for caffeine levels to drop back to half of what they were at their peak. That’s why you should avoid coffee in the four to six hours before bedtime, says Peter Rogers, professor of biological psychopharmacology at the University of Bristol.
Caffeine suppresses melatonin, the hormone that helps us relax and prepare for sleep, and interferes with a brain chemical, adenosine, which normally slows down nerve cells in the brain, making us drowsy.
But don’t rely on caffeine as an energy booster long term. Studies have shown that people who regularly drink coffee to remain alert become tolerant to caffeine, so they are no more alert after drinking it than non-coffee drinkers.
If you think you drink too much coffee, don’t go ‘cold turkey’ as it can cause nasty withdrawal symptoms, says Professor Bazire.
His advice? ‘Cut down on your intake gradually, alternating decaf coffee with your usual cup until you’re drinking no more than three cups in any 24-hour period. Then coffee can be a pleasure.’