Caffeine: The facts

Sophie Edgington - Nutritionist | 19 Oct, 2020

Whether you’re a coffee lover, tea enthusiast, or are perhaps quite partial to both, many of us rely on a caffeine hit in the morning to help kick-start our day and give us that extra burst of energy we need to tackle the tasks ahead.

But what actually is caffeine? Without delving too deep into the science, in short caffeine is an alkaloid occurring naturally in certain seeds, nuts and leaves in around 60 plant species. It is the most widely consumed psychoactive substance in the world and is technically classed as a legal ‘drug’ because it stimulates the central nervous system, causing increased alertness.


UK recommendations

There is no ‘safe’ level of intake as such, because like any drug, caffeine exerts different effects from person to person. This can depend on:

  • Weight and height
  • Whether you’re taking medication and how much
  • Individual sensitivity to caffeine
  • How often you usually consume caffeinated products

However, guidance from the NHS advise against consuming more than 400mg of caffeine a day for adults (the equivalent of roughly four cups of coffee) and no more than 200mg of caffeine a day for pregnant women. These guidelines are based on evidence that suggests consuming up to this amount of caffeine per day won't heighten the risk of any adverse long-term health effects. Without knowing how much caffeine naturally occurs in our favourite beverages, sticking to these guidelines can be tricky!

Coffee is the UK’s caffeine fix of choice

According to the National Diet and Nutrition Survey, coffee is by far the largest contributor of caffeine to the average UK diet, with tea coming a close second. In fact, approximately 95 million cups of coffee are drank every day in the UK and it’s estimated that we will spend more than £4bn getting our caffeine hit from high street coffee shops and cafes this year.

But high levels of caffeine aren’t just found in coffee

To be able to watch your intake, it’s important to consider that caffeine is present in lots of popular food and drinks other than coffee.

Rockstar can (500ml) 200mg
Large cup of filter coffee (500ml) 180mg
Relentless can (500ml) 160mg
Monster can (500ml) 160mg
Cup filter coffee (200ml) 90mg
Redbull can (250ml) 80mg
1 shot espresso 80mg
Cup of instant coffee (200ml) 63mg
Cup of black tea (220ml) 50mg
Diet Coke can (330ml) 42mg
Green tea (200ml) 35mg
Coca-Cola can (300ml) 32mg
Coke Zero can (330ml) 32mg
Small dark chocolate bar (50g) 25mg
Cup of coffee shop hot chocolate (200ml) 25mg
Cup of decaf coffee (220ml) 3mg

Busting the caffeine myths

  • ‘The caffeine content of coffee is far greater than tea’ – interestingly, tea actually contains more caffeine than coffee on a dry weight basis! But as we consume less tea when preparing a brew compared to coffee, the amount of caffeine we actually consume is much less overall.
  • ‘An espresso is the best option to get through an all-nighter’ – not necessarily. A single shot of espresso often contains less caffeine (approx. 80mg) than a mug of filter coffee (approx. 90mg), due purely to the size of the cup.
  • ‘All shop-bought coffees have a similar caffeine content’ – not so - the caffeine content of a cup of coffee can vary greatly depending on; cup size, how finely the coffee is ground, how dark the roast, the brewing method used, how much coffee is used to make the drink and the type of coffee bean used.
  • ‘White teas always have less caffeine than black teas’ – this is a common assumption, however the type of tea isn’t the biggest influence on caffeine content. It is instead largely determined by how it’s been brewed; hotter water and a longer steeping time will result in more caffeine being released from the leaves. In fact, in its dry state, white tea often contains the most caffeine because it is the least processed.
  • ‘You can swap to a caffeine-free tea to reduce intake’ – this is kind of true, as there are plenty of caffeine-free varieties of fruit and herbal teas to choose from, however no black, white or green teas are naturally caffeine-free because they all come from the Camellia sinensis plant.
  • ‘Caffeine can’t kill’ – although incredibly rare, an overdose of caffeine can be fatal. It’s incredibly hard to consume levels high enough (about 100 cups of coffee in a 2-3 hour period), but if regularly combining various types of caffeine-rich products i.e. slimming medications, caffeinated energy drinks etc., the amount of caffeine can really build up. Often the nutritional labels can also be misleading – you may be consuming what you think is 42mg caffeine, when in reality that is the content in 100ml rather than your serving.
  • ‘Coffee is dehydrating’ – Although it’s true that coffee does have a diuretic effect, studies have shown that you’d have to drink an excessive amount for it to actually cause enough fluid loss for it to be dehydrating. For this reason, coffee can be counted towards your 6-8 glasses of fluid per day using the Nutracheck water tracker, although its recommended that tea and coffee should make up less than half of your daily fluid intake, as they are not as hydrating as pure water.

Surprising food and drinks that contain caffeine

Cereal Some breakfast cereals
Ice Cream Coffee-flavoured ice-cream & yoghurts
Decaf Decaf coffee
Weight Loss Weight loss aids
Kombucha Kombucha
Matcha Matcha


Is caffeine a concern?

Caffeinated products play a dominant role in modern society, so it’s important to be aware of any potential health risks linked to caffeine consumption.

Worsened menopause symptoms

Caffeine and alcohol have both been shown to make hot flushes, experienced by women during the menopause, worse – especially in those people already sensitive to the effects of caffeine.

Heightened anxiety

In certain groups, such as those with diagnosed anxiety disorders, some reports indicate increased levels of anxiety and impaired sleep when consuming large amounts of caffeine (more than 5 cups of coffee a day).

Short term health effects

Some individuals may experience adverse effects relating to the central nervous system including interrupted sleep, headaches, irritability, and behavioural changes. Some studies have also indicated increased incidences of aggressive behaviour among adolescents regularly consuming caffeinated products, especially popular caffeinated energy drinks.

High blood pressure

The NHS suggest that drinking 4 or more cups of coffee a day (equivalent to approx. 400mg caffeine) may increase blood pressure, so recommends sticking to within the UK guidelines. Conversely, some studies indicate that coffee contains beneficial compounds such as antioxidants which may have a protective effect on blood vessels. So, as always – eat a healthy balanced diet as everything is fine in moderation.


Those choosing to cut down on caffeine may experience withdrawal symptoms such as headaches, low mood, fatigue and tremors if they stop suddenly, therefore it’s advised to reduce caffeine intake gradually over time.

Coffee Desk

Are there any benefits?

Caffeine gets a lot of bad press, but when drank in moderation, the effects often appear more positive than negative.

Sport endurance

Drinking a cup of coffee 30 minutes before exercise can allow you to exercise for up to 30% longer. This is thought to be down to stimulation of the central nervous system, making exercise feel like less of an effort and reduces pain. Also, during high intensity activities caffeine may increase the number of fibres used in muscle contraction, meaning movements may be more forceful.

Increased alertness

As already mentioned, caffeine has been shown to both increase alertness and reduce fatigue, which is especially beneficial in low arousal situations, such as working late at night. It also may improve the performance of intricate tasks that require close attention, as well as simpler tasks that require greater patience to complete.

Mood enhancer

Low to moderate caffeine intake (2-5 cups a day) has been associated with increased ability to feel pleasure and reduced anxiety. The anticipation of drinking coffee, as well the actual drinking process, is thought to be a mood booster for many, due largely to its ‘comforting’ feeling.

Reduce depression  

Some studies have suggested that increased caffeine consumption, particularly in the form of coffee, is consistently associated with lower risk of depression. The reason why coffee may have a greater protective effect against depression compared to other caffeinated beverages is thought to be due to other components in coffee, including chlorogenic acid, ferulic acid, and caffeic acid, which may work to reduce nerve cell inflammation.

Metabolism boosting

Further research is required in this field, however initial research has speculated that caffeine may help to heighten metabolic rate and therefore help burn more energy during both activity and rest. There are also interesting associations being made between coffee intake and appetite regulation, with potential implications for weight management treatment.

Take home messages

  1. Other than coffee and tea, caffeine is found in many other, often surprising, commercially available foods and drinks.
  2. It's fine to drink tea and coffee as part of a balanced diet, but it's important that these drinks are not your main or only source of fluid.
  3. Evidence to date suggests that for most people, consuming a moderate intake of caffeine (400mg or less) has largely positive effects on behaviour, mood and alertness, however excessive consumption can lead to problems, especially in sensitive individuals.

Nutritionist Sophie Edgington (ANutr), BSc Nutrition is passionate about practising evidence-based nutrition and debunking the multitude of inaccurate myths that so readily surround food and health information. Her goal is to ensure we are all able to make informed and responsible decisions regarding our health.