Warning to coffee drinkers who like milk in their drink

It’s our favourite caffeine fix, but your morning pick-me-up could be impacting your body in unexpected ways, from hair and skin to long-term dental health

Coffee has overtaken tea as the nation’s favourite hot drink and we now get through 98 million cups every day. But coffee is far more than just a caffeine fix, it’s also high in soluble fibre and plant compounds that have a wide range of effects on health. So what exactly does it do to your body?

Once, it was a cup of tea that woke the nation up. Now, 63% of adults regularly drink coffee, compared with 59% who reach for tea. The variety of ways it can be served – from iced lattes to martinis – means it has become a national obsession, with one in six of us visiting a coffee shop to buy one every day. But considering its properties, how much is safe to drink?

Nutritional therapist and pharmacist Deborah Grayson, of Digestion with Confidence, says: “There’s a lot of debate about what level is safe, as it largely depends on your ability to metabolise caffeine, which is influenced by genetics, and overall health.

“Certain heart ­conditions, for example, can be worsened by caffeine. But the general consensus is 400mg of caffeine per day is safe. Since coffee contains between 70 to 150mg of caffeine per cup, depending on the type and strength, that means that most people can safely drink between two and four cups a day.”

How it affects…

Your brain

One of the main reasons we drink coffee is for its ability to wake us up. Its power is down to the way it stimulates feel-good chemicals, like dopamine, in the brain, which makes neural networks work faster, triggering fight-or-flight hormones. But taken at the right time, it can also boost your memory.

READ MORE: Warning to coffee drinkers who take vitamins

A 2018 study in Nature Neuroscience found people who took a 200mg caffeine tablet – about two cups of coffee – after studying a series of images remembered them better the next day compared to people given a placebo. However, the flip-side is that once we’ve used coffee to wake up our brains, it can be hard to switch off the effects, says neuroscientist Anne-Sophie Fluri, who runs Brainwave workshops on how to maximise brain power.

This is because it blocks receptors in the brain for the chemical adenosine, which makes us feel sleepy and relaxed. “Caffeine has a half-life of around five to six hours,” she says. “That means half of the caffeine you’ve consumed is still in your body after this time. How quickly your body breaks down caffeine can vary depending on your metabolism and liver enzymes.”

To make matters worse, once you do eventually drop off, the caffeine in coffee will also stop you getting a good night’s sleep too. A study published in the Journal of Clinical Sleep Medicine in 2013 found that drinking caffeine up to six hours before bed “significantly” disturbed sleep, cutting total sleep time by more than an hour and reducing slow-wave sleep, key for storing memories.

Your teeth

While coffee may taste delicious, it’s not great for your teeth or breath. Over time, drinking it in large amounts can cause tooth discolouration and contribute to bad breath, says Dr Nyree Whitley, chief clinical officer of mydentist.co.uk. “Coffee is high in acidity, which can erode enamel and increase plaque build-up,” she says. “This makes your teeth more susceptible to decay, particularly if you take sugar in your coffee or have syrup flavourings.”

When you add milk to your coffee, it can also be a recipe for bad breath, adds Dr Whitley. “Coffee reduces saliva production, allowing bacteria to thrive and leading to bad breath. It also has a drying effect, which can lead to the production of sulphur compounds in the mouth.”

Your skin

“Coffee is a paradox for your skin. It can be both a protector and a destroyer of youthfulness,” says Dr Laura Geige, cosmetic dermatologist at It’s Me and You. “Caffeine is a powerful antioxidant that helps neutralise free radicals, which accelerate ageing. However, chronically elevated cortisol depletes collagen – the building blocks of the skin, weakens the skin barrier and leads to fine lines and loss of elasticity faster than natural ageing alone.”

Your hair

Drinking a lot of coffee can flush essential minerals from the body, including iron, which is crucial for healthy hair growth, says trichologist Iain Sallis of Hair Medic. “Our body needs good supplies of certain vitamins and minerals for good hair condition and pigmentation, including selenium, zinc and copper.

“So, if we’re consuming lots of black coffee, this will affect our body’s mineral stores, which in turn could have a negative impact on hair condition, including shine and texture.” This loss of iron from caffeine overconsumption may even trigger hair loss, according to Iain. “Iron is needed for healthy hair growth. When it’s lacking, it shortens the growth cycle, making it fall out more quickly, especially for women, who are already more susceptible to low iron levels due to menstrual blood loss.”

Your bones

Drinking too much coffee has been found to hinder the absorption of the calcium we need to keep our skeleton strong. A study from Norway, of nearly 20,000 women found that drinking nine or more cups of coffee per day increased the risk of bone fractures. According to nutritional therapist Deborah Grayson: “Extremely high levels of caffeine intake can reduce calcium absorption and reduce bone density, especially if you already have a low intake of calcium in your diet.”

Your weight

Caffeine is a natural fat burner, increasing metabolism-boosting adrenaline and helping release fatty acids from tissues. Deborah says: “Drinking two to four cups of coffee can suppress appetite and lower the number of calories consumed in a meal, while three to five cups can reduce the risk of type 2 diabetes.”

Your gut

When you think of ways to get your daily fibre, drinking coffee probably doesn’t jump to mind. But coffee is high in soluble fibre – a type that turns into a gel when it’s digested in the intestines. A 100ml cup contains between 0.47 and 0.75 grams of fibre – a third of the amount in a banana.

This fibre helps form a gel that lines the walls of the intestines where it encourages the growth of healthy gut bacteria, according to a study published in Nature Microbiology. This has been found to reduce inflammation in the gut, boost immunity, reduce the risk of type 2 diabetes, and slow down cancer growth. Its high fibre content may also help explain why, on an empty stomach, a strong coffee can speed up the transit of food through the gut, particularly for people with irritable bowel syndrome.

Your ovaries

If you’re trying for a baby, it’s wise to cut down on caffeine. A study in the British Journal of Pharmacology found caffeine interferes with the muscle contractions in the fallopian tubes, needed to move the eggs from the ovaries to the womb. It may explain why women who drink more than 300 milligrams of caffeine daily – around three cups – have been found to have a 27% lower chance of getting pregnant.

Your bladder

Caffeine speeds up how fast your body makes urine, which can leave you feeling dehydrated and needing the toilet more. It also stimulates the detrusor muscle, which contracts to squeeze out wee. A study by the University of Alabama found that women who drank more than three cups daily were 70% more likely to suffer from bladder problems.

The effect it has on your heart

If you have high blood pressure or heart rhythm issues don’t overdo the coffee, warns nutritionist Rohini Bajekal. “Men who have blood pressure issues or heart rhythm issues should be cautious,” she says. “The caffeine can temporarily increase blood pressure and heart rate, so men with heart conditions might consider limiting intake or choosing decaf versions.”

If you don’t have a heart condition, in moderate amounts, coffee has been found to be good for cardiac health. According to a study in the European Journal of Preventive Cardiology in 2022, those who drank two to three cups of coffee each day had a lower risk of cardiovascular disease and early death than people who didn’t.

Research from Johns Hopkins University also found regular coffee consumption can cut stroke risk by 20%, possibly because plant compounds help reduce inflammation and keep the blood vessels open.