I’m a dietitian – the signs that you’re drinking too much caffeine

Millions of us rely on a cup of coffee to give us a desperately-needed jolt in the morning.

But, from a racing heart to constantly needing to urinate, your body can feel the effects of glugging too much caffeine.

Here, dietitians break down exactly what happens to your body when you overdo the coffee…

Whether it is tea, coffee or an energy drink, caffeine has the ability to give a boost in mood, energy and performance, but it can cause anxiety, increased heart rate and higher blood pressure

Whether it is tea, coffee or an energy drink, caffeine has the ability to give a boost in mood, energy and performance, but it can cause anxiety, increased heart rate and higher blood pressure

Drinking more than four cups of coffee could cause you to have unpleasant side effects from caffeine, experts say

Drinking more than four cups of coffee could cause you to have unpleasant side effects from caffeine, experts say

High blood pressure

Drinking more than four cups of coffee a day can cause blood pressure to rocket.

That’s because caffeine delivers an energy boost by blocking adenosine receptors — the chemical responsible for feelings of sleepiness.

Like a lock and key, caffeine fits into the adenosine receptors, said Dr Duane Mellor, based at Aston University. 

However, this same mechanism is also thought to trigger a hike in blood pressure within half an hour of drinking coffee, tea or cola — and the effects can still be seen roughly four hours later.

Dr Mellor said: ‘This impact is variable and can reduce in some people over time as the ability of caffeine to affect adenosine reduces with habitual consumption.’

What contains caffeine and how much is safe to drink?

  • Coffee, tea, colas and energy drinks contain high amounts of caffeine. 
  • Caffeinated drinks are unsuitable for toddlers and young children
  • Pregnant women should have no more than 200mg of caffeine a day because high levels of caffeine can result in babies having a low birthweight
  • The NHS suggests that more than 600mg of coffee per day (six cups) is too much and can lead to anxiety, sleeplessness and palpitations 
  • One mug of instant coffee contains around 100mg of caffeine
  • Energy drinks can contain 80mg of caffeine in a small 250ml can. This is the same as two cans of cola or a small mug of coffee
  • The NHS advises that tea and coffee is fine to drink as part of a balanced diet
  • But caffeinated drinks can make the body produce urine more quickly 


As well as this temporary effect, the NHS warns that drinking four cups of coffee per day may increase your blood pressure in the long run. 

Frequent toilet trips

Needing to pass urine frequently may be another tell-tale sign you’re consuming too much caffeine. 

The stimulant boosts blood flow to the kidneys and reduces the amount of water and sodium absorbed by the body — increasing the need to urinate.

These frequent toilet trips can make you dehydrated, which can cause headaches.

However, this side effect is usually only seen among people who are increasing their caffeine intake, rather than those who consume a steady amount, according to Dr Mellor.

And those who only drink a couple of cups of coffee a day may not suffer it at all.

Jennifer Low, a Kent-based registered dietitian, said those who drink less than 6mg per kg of body weight per day won’t see any affect on their urine output.

This is around 510mg of caffeine for an average man in the UK, who weights 85kg, and 432mg a day for the average woman, who weighs 72kg — equating to five or four cups of coffee, respectively.

Abdominal pain

You may have an upset stomach after glugging too many cups of coffee.

Coffee and tea consumption has been linked to irritable bowel syndrome symptoms, acid reflux, abdominal pain and loose stools, Ms Low said.

But the evidence that caffeine itself is the culprit is currently limited, she noted. 

‘Caffeine may have less effect on the bowel — often it is the effect of hot drinks that speed up the waves through our digestive tract’, said Dr Mellor. 

However, caffeine can increase the productions of stomach acid which can cause ‘reflux and heartburn’, he added. In some people, it is accompanied by stomach pain.  

Caffeine has also been shown to have a stimulant effect on the digestive system, which can lead to an upset stomach. 


Caffeine is a stimulant, so it is no surprise that people feel jittery and restless after drinking a few too many cups of coffee or cans of energy drink.

Any more than four cups of coffee a day is enough to bring on feelings of nervousness, anxiety and an increased heart rate, experts say. 

This is because caffeine raises the body’s heart rate and the amount of blood leaving the heart, which can leave the organ racing, according to Dr Mellor.

It also increases brain activity, which can contribute to feelings of anxiety, he said.  

Additionally, it disrupts sleep which can make it harder to control anxious feelings, such as worry, fear and a sense of dread, the NHS warns. 

Ms Low said: ‘Patients do report increased heart rate, and in patients I see, with eating disorders, who often also have anxiety, this increased heart rate can be attributed to anxiety, which then can make them feel more anxious. 

‘In most of my patients I recommend they switch to decaffeinated.’ 

What are the benefits of quitting coffee?

Once you have put yourself through a banging headache, nausea, tiredness and brain fog, you may be wondering what the benefits of quitting even are. 

According to experts, better sleep, whiter teeth, lower blood pressure and less anxiety are some of the long-term positives you could experience after giving up, if you can bare the temporary side-effects.  

Harley Street nutritionist Kim Pearson believes that having severe withdrawal symptoms could be a sign you were consuming too much caffeine in the first place. 

She said: ‘If you’re experiencing withdrawal symptoms, it’s a sign you’ve been consuming too much and have become dependent on it. Caffeine is a drug after all. 

‘If you have been over consuming caffeine then coming off it for a while, or at least cutting down, is a good idea.’  

However, she adds that research has also shown that coffee consumption can help reduce the risk of certain diseases including Alzheimer’s, Parkinsons and certain cancers. 

Ms Taylor, of the British Heart Foundation, explained caffeine, if consumed in moderate amounts, is not bad for your heart. 

She said: ‘Although coffee is often thought as something we should give up to protect our heart health, that’s not necessarily the case. 

‘For most healthy people, a moderate intake of caffeine shouldn’t be detrimental to your heart health, for example, around four to five cups of tea or coffee a day.’

She added: ‘Coffee has been shown to increase blood pressure, but this effect is usually temporary and is minimised over time if you drink caffeinated drinks regularly.’

She added that it is not just caffeine you should be wary of if you are concerned about your heart health, but also sugary drinks. 

She said: ‘If you want a healthy cup of coffee avoid added syrups, sugar, cream or large milky coffees – they all add up in terms of sugar, calories and saturated fat.’

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