Everything you ever wanted to know about caffeine

Got a question about caffeine? We've put together an extensive guide to the world's favourite morning pick-me-up. If you can't find the answer to your question here, pop us a mail at advice.centre@dnafit.com. We'll get one of our wellness team to help you find the information you need.

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What is caffeine?

Caffeine is a stimulant that affects our central nervous system. Because of this, caffeine is actually classified as a drug. In fact, up until 2004, caffeine consumption was considered doping at the Olympics - which could even lead to disqualification. Caffeine is considered the most widely used drug in the world. “The caffeine limit as imposed by WADA/IOC has varied over the years from 12 to 15 mcg caffeine per liter (L) of urine or approximately 1,000 mg (or six to eight cups of coffee, 8 to 12oz) consumed within a relatively short period of about 1 hour”, writes Coffee Chemistry.

Recent figures from the British Coffee Association state that 95 million cups of coffee are consumed daily in the United Kingdom, showing a year-on-year increase in daily caffeine intake.

The effects of caffeine include:

  • Reduced feelings of physical fatigue
  • Increased thought-processing
  • Improved focus and concentration

What caffeine does to your body

We all have a chemical in our cells called adenosine. It has various functions in our body one of which is to promote sleep. Caffeine can block adenosine from reaching its receptor, therefore, making us feel more active and less tired.

The effects of caffeine are quite mild and generally only last for a short period of time.

Where is caffeine found?

Caffeine is mostly associated with coffee and caffeinated energy drinks - but, it’s also found in a number of foods. Today, caffeine is readily available to everyone (young and old), and you would be hard-pressed to find someone who’s never consumed caffeine before.

What drinks are high in caffeine?

  • Coffee (95mg)
  • Tea (45mg)
  • Hot chocolate (6mg)
  • Energy drinks (80mg)

What foods are high in caffeine?

  • Dark chocolate (20mg)

What is the recommended daily amount of caffeine?

As a general rule, the your daily caffeine intake shouldn’t exceed 300-400 mg, which equates to two to three cups of coffee per day. Of course, we know that your genetics can also impact how you metabolise coffee, which we will go in to in detail in the next section of this article. DNA testing determines how much caffeine is safe for your body.

Caffeine and genetics

What you’ll learn from your DNAFit reports with regard to caffeine sensitivity, is that certain genes indicate whether you’re a fast or slow metaboliser of caffeine.

  • Fast metabolisers can consume a moderate amount of caffeine (300-400 mg), as their bodies utilise it quicker. They are less likely to see negative side effects from caffeine consumption.
  • Slow metabolisers are advised to consume less caffeine (no more than 200 mg) to avoid the potential unpleasant side effects of excess caffeine intake.

What genes are associated with caffeine sensitivity?

The main gene when it comes to caffeine sensitivity is CYP1A2. The enzyme produced by this gene is responsible for about 95% of all caffeine metabolisation. Different people have different versions of this gene, which can make this enzyme work faster or slower.

Research on the effects of caffeine on cardiovascular health found that the effect of caffeine differs between genotypes. With regard to caffeine response, AA genotypes tend to metabolise caffeine quicker than AC and CC genotypes. As a result, AA genotypes are called “fast metabolisers” and the AC and CC genotypes are classed as “slow metabolisers”.

A 2006 study found that slow metabolisers who had more than about three cups of coffee per day, increased their risk of suffering from a myocardial infarction (heart attack). Fast metabolisers, however, didn’t see an increase in heart attack risk.

The same is true for hypertension. A 2009 study found that higher amounts of caffeine (around 300mg per day) was associated with an increased risk of hypertension – but only in slow caffeine metabolisers. Based on these studies, and others like them, DNAFit recommends that slow metabolisers should limit their intake of caffeine to around 200mg per day. Fast metabolisers can consume more caffeine should they wish, up to approximately 300mg per day.

VDR is included in the panel because variations in this gene determine if excessive caffeine intake has a negative effect on bone mineral density. Carriers of the AC and CC genotypes are advised to limit their caffeine intake, regardless of whether they are fast or slow metabolisers.

What are the side effects of caffeine?

Caffeine has both short and long-term side effects.

Short term effects of caffeine

Caffeine has a number of short term side effects which can be both positive and negative. The effect of caffeine varies from person to person. As stated before, caffeine is a stimulant and therefore acts as such.

Short term effects of caffeine include:

  • Alertness
  • Increased energy
  • A boost in brain function
  • May trigger weight loss through appetite suppression

You should always take these into account when considering drinking coffee at the night time, as it may result in sleeplessness and could also cause heartburn.

We’ve also touched on your genetic response to caffeine, which is important to consider. Depending on your sensitivity, you may see slightly different side effects. Doing a DNAFit DNA test will allow you to gain insight into your response to caffeine and how you should manage your daily intake accordingly.

Long term effects of caffeine

Genetically we only look at the effect of caffeine on blood pressure. Keep in mind genes are just one component and lifestyle is another. If you constantly have caffeine then your body will adapt to it, however if you only have it now and then, then your body is not desensitised to it and this could result in various adverse side effects such as vomiting, diarrhoea, nausea and tremors.

Can you overdose on caffeine?

In extreme cases, caffeine overdose can actually have very serious consequences. Too much caffeine is even harmful to people who are considered fairly healthy. Some side effects of extreme caffeine overdose include restlessness, insomnia and muscle twitching. Or in very severe cases it might induce temporary mental disorders as well as death.

If you just looked at your coffee cup with dread – don’t worry. You’d have to consume around 75-100 cups of coffee to induce the very severe caffeine overdose symptoms. So that third cup of coffee you’re having right now is probably not going to kill you.

People with heart problems and hypertension, however, should watch their caffeine intake more carefully, as it may have a stronger effect on their heart rate and blood pressure.

Can caffeine improve performance?

When we’re feeling tired, we often reach for the coffee pot. That’s because caffeine has the ability to wake us up, making Monday morning slightly more tolerable. This fact has not been lost on sports people, who for years have been using caffeine in the hope that it can improve their sporting performance.

But is this actually the case?

The short answer is a resounding yes. Caffeine really can improve performance, and there are a host of research articles showing this.

Time and time again the research shows that caffeine can improve muscular endurance, performance in intense activities, and also performance in endurance activities. The typical amount of caffeine that is recommended from research like this is somewhere between 3-6 mg of caffeine per kilogram of bodyweight; so, for a typical 80 kg male this would be somewhere between 240 mg and 480 mg. 240 mg of caffeine is the equivalent of around two to three cups of coffee, and three cans of energy drinks – not a small amount at all.

The next thing to consider is how caffeine creates these positive effects. Here the research is a bit less clear, although there are a few mechanisms which have been put forward with plenty of support.

Caffeine and Fat

The first of these is that caffeine might make it easier for us to burn fat, where in endurance events fat is the main source of fuel. One way caffeine does this is by increasing the use of free fatty acids as a fuel.

Caffeine and Adrenaline

Another idea put forward by researchers is that caffeine causes an increase in adrenaline, which in turn can improve performance. Caffeine also appears to have an effect on the brain, making exercise feel easier, which in turn means that athletes are able to keep going for longer.

Caffeine and Adenosine

A final potential mechanism is that caffeine competes with something called adenosine. Adenosine causes muscles to relax and can cause the nervous system to slow down, making us sleepy and relaxed. Caffeine can out-compete adenosine to join with its receptors, making us less susceptible to the effects of caffeine.

One thing that is interesting from the research surrounding caffeine is that it doesn’t affect everyone to the same extent. In some people, caffeine really does improve performance, and can have a large effect. However, in other people this effect can be much smaller, and in some cases caffeine actually makes performance worse. One factor that might play a role here is our genes.

Research on caffeine and performance

Research in this area is very new, and there are less than a handful of studies. However, the most well-known of these studies, from 2012, found that caffeine improved endurance exercise performance to a greater extent in fast metabolisers of caffeine than slow metabolisers. This goes some way to explaining why some people find caffeine improves their performance, and others don’t.

DNAFit is constantly conducting our own research in order to ensure that what we do is essentially grounded in science. We briefly reviewed the drivers of this inter-individual variation in caffeine response, focusing on the impact of common polymorphisms within two genes, CYP1A2 and ADORA2A.

Contemporary evidence suggests current standardised guidelines are optimal for only a subset of the athlete population. Clearer understanding of the factors underpinning inter-individual variation potentially facilitates a more nuanced, and individually and context-specific customisation of caffeine ingestion guidelines, specific to an individual’s biology, history, and competitive situation.

So, while the research is still expanding, there is evidence that suggests a relationship between caffeine, performance and genetics that could assist athletes in the way that they train.

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