Most of us are familiar with the most obvious impacts of coffee, both good and bad. It can make us more mentally alert – which is great if we need waking up – but it can also make it harder to get to sleep if we drink it too close to bed time. This is because caffeine, the ingredient responsible, happens to block the effects of a molecule called adenosine, which is involved in nerve cell signalling all over the body. Adenosine normally promotes sleepiness, which is why caffeine is a potent mental stimulant. But caffeine has several other effects on the body, impacting everything from our muscles, to our heart and our bowels. Here are some of caffeine’s lesser-known impacts on our physical health. (Photo: iprogressman/Getty/iStockphoto)

1) Keeping up strength in older people

People who drink at least four cups of coffee a day are less likely to get frailer as they age, according to a recent study of over a thousand Dutch people in their fifties or older. Medical fraility is a term used by doctors to mean that people have low muscle strength and may also have other conditions like vision or hearing problems that lead to a higher risk of becoming ill. The study was not the best kind of medical evidence, a randomised trial, so it could not prove that coffee was directly causing the benefit. But in studies of mice, adding coffee to their diets slowed their loss of muscle as they aged. “These findings suggest that habitual daily coffee consumption may contribute to improved health in older individuals,” said the Dutch researchers. The results were published in the European Journal of Nutrition. (Photo: Maskot/Getty)

2) Heart health

Coffee has come under suspicion in the past, as some older studies suggested it was linked with worse heart health. But these were also observational studies, prone to producing biased results, and it seems the correlation arose because people who drank more coffee were also heavier smokers. Coffee does have some noticeable immediate effects on the cardiovascular system in people who are not used to it. It can slightly raise heart rate and blood pressure. But these effects are temporary and tend to fade in those who regularly drink the same amount each day, causing their bodies to adjust. If someone drinks much more than usual, though, caffeine may cause heart palpitations, when the heartbeat becomes irregular. It can sometimes be noticed as a fluttering sensation in the neck or chest. In terms of long-term effects, the thinking now is that coffee drinking either has no impact on the heart, or may even somewhat lower deaths from heart disease. The largest study to investigate this question, in half a million Britons, found that having up to three cups of coffee a day was linked with lower rates of heart disease when compared with drinking no coffee. People with higher coffee intakes had similar rates as abstainers. “Our results suggest that regular coffee consumption is safe, as even high daily coffee intake was not associated with adverse cardiovascular outcomes,” said the authors. (Photo: Yuichiro Chino/Getty)

3) Triggering bowel movements

As a stimulant, caffeine speeds up movement of food through the gut, and can trigger a bowel movement, especially when taken as a morning coffee. “In the morning our digestive system is more primed and ready to have a bowel movement,” said Rebecca McManamon, a consultant dietitian and spokesperson for the British Dietetic Association. For anyone who is prone to diarrhoea, too much caffeine can be unwise. But it can be helpful for people who are constipated, she said. Furthermore, because it is made from the beans of the coffee plant, it is a source of soluble fibre, which also helps promote regular bowel movements. Coffee has about 1g of fibre per cup or more, depending on the type, with drinks made from instant coffee tending to have more than ground coffee. We are advised to have 30g of fibre a day but the average for UK adults is 20g. So, if people have several daily cups of coffee, it can help them reach the recommended amount. (Photo: Sevda Ercan/Getty/iStockphoto)

4) Source of hydration

Caffeine is known to mildly stimulate fluid output, so some people mistakenly think that tea and coffee shouldn’t be seen as a source of hydration – but that’s wrong, said McManamon. In fact, caffeine has only a mild effect in this way, which is easily outweighed by the water component of the hot drink. If you are trying to make sure you don’t get dehydrated in the hot weather, it’s fine to drink coffee and tea as usual for hydration. “Some people don’t enjoy drinking water,” she said. “If they do drink coffee, that’s going to help them drink enough in this warm weather, so that’s absolutely fine.” (Photo: Tom Werner/Getty/Franziska)

Drawback: Reducing calcium levels

One drawback of coffee is that caffeine slightly raises the amount of calcium that is excreted in urine, which could make it more likely that bones become weaker. “In theory, this could lead to your bones losing strength if you don’t consume enough calcium to replace it,” says the Royal Osteoporosis Society. The organisation recommends that if people are at risk of weaker bones, they should stick to having only four cups of coffee a day, and could balance out any effect by drinking their coffee milky. Sources of calcium include cheese and other dairy foods, as well as green leafy vegetables. (Photo: lechatnoir/Getty/E+)