Many of us enjoy our morning cup of ‘joe’ as a pick-me-up and start to the day. In fact, coffee as an example is the world’s most consumed beverage after water clearly highlighting the enjoyment many of us take from this drink. While some of us may enjoy the taste of coffee, we are more than likely after the associated caffeine hit as opposed to the taste. Caffeine is a naturally occurring substance found in plants, most notably coffee beans and tea leaves. It is also man-made, and is added to many types of food, drink, and medications, but, how does it affect our bodies and what impact can it have on sports performance?

Caffeine’s effect on the body

Caffeine has a number of effects on the human body…

How caffeine affects the Central Nervous System

Most people know that caffeine acts as a stimulant on the central nervous system and the most noticeable effect is alertness. For this reason, it’s a common ingredient in medications to treat drowsiness. However, if you’re not used to caffeine, you may experience side effects such as anxiety, jitters or sleep disorders. Another side effect of caffeine is headaches

How caffeine affects the Digestive and Excretory systems

If you have stomach problems such as acid reflux or ulcers it’s probably best to give caffeine a miss. One of the notable effects of caffeine is an increase in the amount of stomach acid which could lead to heartburn. One of the common misconceptions is that caffeine will cause dehydration. Whilst caffeine is a diuretic, the amount of water in a cup of tea or coffee negates the water loss, but other forms of caffeine can cause dehydration.

How caffeine affects the skeletal and muscular systems

Caffeine interferes with the absorption and metabolism of calcium especially in large amounts, so if you are worried about brittle bones time to lower your intake.

How caffeine affects the circulatory and respiratory systems

Caffeine reaches its highest level in the bloodstream one to two hours after you ingest it. Once caffeine is in the bloodstream it can increase your blood pressure for a short period of time and can make your heart work harder, in healthy adults this is fine but in adults that suffer from hypertension or arrhythmia or any other heart-related problems, it’s best to ask your doctor if caffeine is safe for you.

How caffeine affects the reproductive system

Caffeine contributes to fibrocystic disease which is painful lumps in the breast. According to the Mayo Clinic, there is some evidence that large amounts of caffeine can interfere with oestrogen production and metabolism, making it harder to get pregnant.

How much caffeine should you consume?

According to the Mayo Clinic, it’s fine for healthy adults to consume up to four hundred milligrams of caffeine per day. The amount of caffeine an individual can tolerate without unpleasant side effects varies greatly based on age, body mass, and health status. Consuming more than four hundred milligrams a day is generally considered too much, by the FDA. That’s the equivalent of four to seven cups of coffee you are using the standard eight ounces’ cup size, but if you’re using a mug or getting your fix at a coffee shop, chances are you’re drinking 16 ounces or more. If you do consume more than four hundred milligrams, it’s best to decrease your consumption slowly, as stopping suddenly can cause symptoms of withdrawal.

What are the Symptoms of caffeine overdose?

When you have had a caffeine overdose you may experience the following:

• Headache
• Confusion
• Hallucinations
• Convulsions in extreme cases.

It will also affect your digestive and excretory system, potentially giving you:

• Diarrhoea
• Excessive thirst
• Increased urination

Your circulatory system does not escape lightly either. You can experience a rapid or irregular heartbeat and breathing troubles. In extreme cases of caffeine overdoses, death can arise due to convulsions or irregular heartbeat.

What are the Symptoms of caffeine withdrawal on our bodies?

Dropping caffeine from your diet too quickly can be almost as bad as consuming too much. If you suddenly stop your regular caffeine intake, you may experience anxiety, irritability, tremors, drowsiness, nausea, and vomiting.

Caffeine in exercise

Despite considerable research in this area, the role of caffeine as a performance-enhancing drug is still controversial. Some of the data are conflicting, which is in part due to how the experimental studies were designed and what methods were used. However, there is general agreement in a few areas:

1. Caffeine does not appear to benefit short term, high-intensity exercise (eg. sprinting)
2. Caffeine can enhance performance in endurance sports.

Glycogen is the principal fuel for muscles and exhaustion occurs when it is depleted. A secondary fuel, which is much more abundant, is fat. As long as there is still glycogen available, working muscles can utilize fat. Caffeine mobilizes fat stores and encourages working muscles to use fat as fuel. This delays the depletion of muscle glycogen and allows for a prolongation of exercise. The critical time period in glycogen sparing appears to occur during the first 15 minutes of exercise, where caffeine has been shown to decrease glycogen utilization by as much as 50%. Glycogen saved at the beginning is thus available during the later stages of exercise. Although the exact method by which caffeine does this is still unclear, caffeine caused sparing in all of the human studies where muscle glycogen levels were measured. The effect on performance, which was observed in most experimental studies, was that subjects were able to exercise longer until exhaustion occurred.

In addition to the beneficial effects on muscle, caffeine may alter the perception of how hard you are working. During testing, athletes are asked to judge their effort, which is referred to as the rating of perceived exertion (RPE). Some studies have yielded significantly lower RPE’s — less fatigue — when the athlete used caffeine. Other studies have not found this effect. Obviously, the RPE is very subjective, and there are many things that may influence it.

What about caffeine in Ironman races?

The exercise studies on caffeine involved endurance testing of approximately 2 hours, so there is no specific information related to ultra-endurance races. Pre-race caffeine may be beneficial though, because the longer the race, the more important fat is as a fuel. During the race, caffeinated soft drinks are one of the choices at the aid stations in an Ironman. Whether this source of caffeine is useful is unknown, but these soft-drinks do supply necessary carbohydrates. Because longer races have a greater baseline risk of dehydration, nausea, and abdominal cramps, it is very important to consider the side effects of caffeine.


Caffeine has its benefits, but if you consume more than the RDA of up to four hundred milligrams, you could be putting a lot of stress on your body and having some bothersome side effects. So stick to the 3-4 caffeinated hot drinks a day, and keep your eye on the other sources of caffeine you are putting in your body.

Just to show you all caffeine is not bad here are ten health benefits from keeping your coffee intake to 3-4 cups of coffee a day.

1. Coffee Can Improve Energy Levels and Make You Smarter
2. Coffee Can Help You Burn Fat
3. The Caffeine Can Drastically Improve Physical Performance
4. There Are Essential Nutrients in Coffee
5. Coffee May Lower Your Risk of Type II Diabetes
6. Coffee May Protect You From Alzheimer’s Disease and Dementia
7. Caffeine May Lower the Risk of Parkinson’s
8. Coffee Appears to Have Protective Effects on The Liver
9. Coffee Can Fight Depression and Make You Happier
10. Coffee Does Not Cause Heart Disease and May Lower the Risk of Stroke