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The Science of Caffeine 


This article was written by Jeni Peters at Future Fit Training.

Five years ago, I decided to give up drinking caffeine. Not an easy decision to make you may be thinking, however, it was a decision that I was passionate about and to this day I am proud to say that a caffeinated beverage has not passed my lips.

With approximately 90% of adults in the world consuming caffeine daily (1) and the UK coffee industry contributing over £17 billion to the economy each year (2), it is clear that caffeine is a staple ingredient in society and people’s lives.

What is Caffeine?

Caffeine is a natural stimulant that can be found in the leaves and seeds of over 60 plants. It can also be man-made and added to products. The cola nut and dark chocolate-coated coffee beans are two foods that are high in caffeine, with one cola nut containing more caffeine than two large cups of American coffee. Other foods that are high in caffeine include chocolate and chocolate frosting on cakes. Future Fit’s Nutrition and Weight Management course covers the basics of caffeine and is a great course to start with to understand more about this stimulant.

What are the Effects of Caffeine?

To ensure our days are productive and so we can use our waking time wisely, we rely on resources to help us. One of these resources is caffeine, which can delay the feeling of tiredness and increase productivity, especially if a good night’s sleep has not occurred. There are too many times I’ve heard people say that they can’t function without their morning coffee every day. 

Here’s the science bit…Sleepiness occurs through the build-up of a chemical in the brain called Adenosine. When we sleep, Adenosine can be metabolised and broken down. Caffeine’s job is to block the receptors in the brain responsible for producing the feeling of sleepiness. When these receptors are blocked after caffeine has been consumed, the individual feels alert and awake and can perform at an optimal level (or so they think). However, these effects are short-lived and after a few hours the alertness wears off and the individual feels sluggish and tired (usually around mid-afternoon), often after the liver has metabolised and excreted some of the caffeine. This leads to the individual reaching for more caffeine to get them through the rest of their day.  Taking on stimulants such as caffeine and dodging sleep stops the breakdown of Adenosine from occurring. As a consequence, the quantity of the chemical present in the brain starts at a higher level the following day, compared to if proper sleep occurred. Here starts a vicious circle of feeling sleepy, taking on stimulants to be alert, feeling sleepy again (at a quicker rate than previously felt), and taking on stimulants again; all of the time not doing what is required, and getting a proper night’s sleep!  

Benefits of Caffeine

Although caffeine may be duped as the enemy that disrupts sleep and recovery for the body and mind, there are benefits to consuming it, especially from a sports performance perspective.

Caffeine can induce alertness by stimulating the central nervous system. Research studies have seen improvements in endurance performance in mentally fatigued individuals (3). This is relevant for those who train in the evening after working all day. Additionally, caffeine can increase the metabolism of free fatty acids. This means that the muscles rely less on glycogen stores during exercise, and they can be preserved until they are needed. The preservation of glycogen is key to maximising performance at the end of an event and being able to put in the hard work right up to the end. Caffeine can give the body the energy boost that it needs! More information on the effects of caffeine and sporting performance can be found in the Nutrition for Sport and Exercise course offered by Future Fit.

Caffeine intake can be affected by the size of the coffee bean, whether the roast is light or dark, the preparation of the coffee, and the size of the serving. On average, an individual who consumes 40mg of caffeine will have 20 mg still within their system after 5 hours (4). To put this amount into context, the caffeine content of a flat white Costa coffee is 227 mg for 92mg consumed (5). The caffeine content can also vary between brands. Black Label Brewed Coffee is believed to have the most caffeine per ounce at 129.6 mg, with Coffee Bean & Tea Leaf’s regular coffee packs containing 20.8 mg of caffeine per ounce. That’s more than twice the amount of caffeine offered in a McDonald’s coffee (9.1 mg per fluid ounce).  Many people move towards herbal teas to try and lower their caffeine intake. Green tea is a popular choice amongst many. An 8-ounce (240-mL) serving of green tea provides about 30–50 mg of caffeine, which is about half of the caffeine content of a cup of coffee (6), making it a good alternative. If you’d like to learn how to plan caffeine into an individual’s diet, check out the Meal Planning online module with Future Fit.

Negative Effects of Caffeine

Even in moderate amounts, caffeine can cause short and long-term effects on the body. Short-term effects include restlessness and shakiness, headaches, dizziness, increased heart rate, dehydration, and anxiety. An intake of more than 600mg per day over a long period can lead to chronic insomnia and anxiety, depression, and stomach problems, and affect blood pressure, deepening any existing medical problems. Long-term use of caffeine can also create a dependency on it, decreasing the benefits that it has on the body and requiring the user to consume more each time.


Caffeine has become an integral part of society, with more people consuming it for both sports performance and to increase their daily living. Although there can be benefits to ingesting caffeine, there are also negatives associated with increased amounts, which may be detrimental to long-term health. It is important to note that all caffeinated beverages will differ in caffeine content and the amount consumed, along with how they are made, needs to be considered when making the choice.  


1 –,the%20world%20consume%20caffeine%20daily.

2 –,retail%20and%20food%20service%20sectors.

3 – McLellan, T.M. et al., (2016) A review of caffeine’s effects on cognitive, physical, and occupational performance

4 – Olsen, N., (2018) How long does a cup of coffee keep you awake?

5 – MacDonnell, K., (2022) How much caffeine is in a Costa Coffee? What to know!

6 –

This blog post was authored by Future Fit Training – a leading training provider, offering courses in nutrition, personal training and much more.

Header photo by Julia Florczak

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