A Doctor's View

Caffeine - Harmful? How much is too much?

May 06, 2020 Dr Polyvios Episode 39
A Doctor's View
Caffeine - Harmful? How much is too much?
Show Notes Transcript

In view of the recent lockdown one thing that a lot of us have probably noticed is just how much tea and coffee we are drinking. This episode looks at the physiological effects of caffeine on the brain and how the effects of adenosine and dopamine help to explain why we love our morning cup of coffee so much. But is our love of caffeine harmful? And how much is too much?

*Contains public sector information licensed under the Open Government Licence v3.0*

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Caffeine Podcast – Show Notes


Hello everyone and welcome to a doctor’s view. Firstly a hello and a very warm welcome to new listeners and a very welcome back regular listeners of the show. If you’re listening at the time that this episode has been published, during the midst of the pandemic which has caused so much tragedy and hardship to so many families, I would like to say thank you to everyone who is helping to save lives by staying at home, I know it’s not easy, I know it’s unnatural but I promise from the bottom of my heart the difference it has made is profound.

In view of the recent lockdown one thing that a lot of us have probably noticed is just how much tea and coffee we are drinking. Personally, I love coffee. I drink quite a lot of it, I am willing to try new flavours and brews and coffee is a drink that a regular coffee drinker is willing to spend hundreds of pounds on each year be it from coffee shops to household coffee machines to roasting their own beans in search for that perfect cup of mystical dark liquid.

So I thought I would talk about what caffeine does to the body, discuss whether it is harmful and also talk about how much is too much. 

Aside from the flavour, the biggest reason we drink tea and coffee is for its caffeine content. Caffeine is the most widely used psychoactive drug in the world. And when you realise just how many drinks and foods contain caffeine, it’s easy to see why.

It’s the caffeine in our morning cup of tea or coffee that gives us that get up and go mentality or makes us feel more awake. It’s often a meme on the internet that some people shouldn’t be spoken to before they’ve had their morning coffee. Caffeine is also the most widely socially accepted drugs in the world. So much so that there is at least 3 coffee shops down any local high street and few of us would ever think to label our favourite drink as a ‘drug’. 

But a drug is exactly what caffeine is. And a powerful one at that.

So what is caffeine? Caffeine is a naturally occurring chemical stimulant called trimethylxanthine. It is found in plant products like tea leaves and of course coffee beans. In it’s purest form it is a bitter white powder and if you’re thinking that it could easily be heroin or cocaine, you’d be correct and it does impact the brain in a similar way all be it to a much lesser extent.

How does caffeine affect our brains? Well the answer is adenosine and dopamine.

Adenosine is an inhibitory neurotransmitter and adenosine receptors are found in organs throughout the body with the majority of effects being on the heart and the brain.

As we go about our working day we require energy. In order to produce energy our body breaks down Adenosine Triphosphate (ATP). One of the end products of this is Adenosine. Throughout our day Adenosine slowly builds up inside our neurons and binds to our adenosine receptors. Now there are different Adenosine receptors. The 2 we are interested in are the A1 receptor and the A2A receptor. The A1 receptor is found on neurones that produce effects to keep us awake and alert so increasing out cardiac output, increasing our cardiac excitability, decreasing our response to insulin, maintaining a high blood pressure etc. When Adenosine binds to the A1 receptor found on these neurones, it has an inhibitory effect. So these effects are decreased; making us less alert. When adonising binds to the A2A, it’s understood that this promotes the releases of neurotransmitters that are responsible for promoting sleep.

So as Adenosine slowly builds up throughout the day it starts to act on these receptors making us less alert and more sleepy. Which is one of the reasons why we are tired at the end of a hard day’s work and all we want to do is go to bed. It’s our body’s incredible way of promoting sleep and telling us it’s time for us to rest.

This is where caffeine comes in. Caffeine has a chemical structure that looks similar to adenosine and is able to fit into the adenosine receptors therefore blocking adenosine from occupying the receptors and activating them. So in science speak, caffeine is a non-selective adenosine antagonist.

So if adenosine can no longer bind to the A1 and A2A receptors we no longer have the mechanism to make us less alert and sleepy and so we feel more awake.

Adenosine receptors are also thought in reducing the activity of neurotransmitters like dopamine. Dopamine makes us feel happy and excited. And it’s this aspect that make us believe why people can become addicted to caffeine. Similar to other drugs, all be it to a much less extent.

So we know how caffeine works to keep us awake and we know it can make us feel good.

The next question is: Is it bad for you? Should we stop taking this psychoactive drug that we know and love immediately?!

In a nutshell, in moderation, caffeine is safe to enjoy. A systematic review conducted in 2017 looking at the potential adverse effects of caffeine amongst a healthy population found that consuming less than or equal to 400mg of caffeine a day (approximately 4 cups of coffee) in a healthy adult doesn't have a negative effect on bone health, heart health, behaviour or on reproduction and development.

However it must be said that this was looking at a healthy population and so there may be an increased risk with people suffering from health problems and whilst 4 cups a day may be ok, some studies have shown that more than this is associated with increased risk of cardiovascular disease, although there may be other confounding factors such as those who are drinking more coffee may also be more likely to smoke more. But it is something to take into consideration.

And whilst it was shown that 4 cups of coffee a day doesn’t have negative impact on cardiovascular disease, we do know that caffeine does temporarily increase blood pressure and we don't know that observations on measures such as blood pressure, anxiety and sleep would necessarily have led to negative overall health outcomes.

As a side note, the NHS here in the UK recommends no more than 200mg of caffeine per day for pregnant women.

The review showed that consumption of coffee led to increases in measures of anxiety and, unsurprisingly given now we know how caffeine works, delays in getting to sleep and decreases in quality of sleep.

Now I’ve touched on caffeine and sleep in a previous podcast with Dr Mike Farquhar discussing sleep and health. For me it is the sleep aspect that I find probably the most fascinating with caffeine and health. Given the number of physical and mental health problems that can arise from poor sleep, it can be argued that caffeine can indeed be harmful in the long-term if it is taken too late in the day, or in excess causing sleep disruption. Some things that are often overlooked is how long caffeine stays in the system. It has a half-life of around 6 hours so 6 hours after taking it half of the caffeine is still in your body. It’s definitely something to think about before having an afternoon coffee or tea; will it affect your sleep later on.

We also sometimes don’t realise how many different foods and beverages contain caffeine. 

We’ll say a cup of brewed coffee is around 100mg of caffeine for reference.

Tea is not caffeine free and neither is green tea, so always look for a herbal tea that says it is naturally caffeine free if you’re trying to avoid a caffeinated drink. The amount of caffeine in tea does vary and although it is not as much as coffee the amount of caffeine does increase the longer the tea is brewed for.

Fizzy drinks can contain quite a lot of caffeine. A can of Coca Cola contains 32mg of caffeine and Diet coke even more at 42 mg.  There is relatively quite a bit of caffeine in chocolate. A bar of dark chocolate can contain around 60mg of caffeine; a 30g serving around 20mg, this can add up especially if you enjoy a hot chocolate in the evening before bed; you might find it’s not so helpful in helping you relax!

It is also worth noting for those who enjoy decaf coffee or tea, decaffeinated is not UNcaffinated. Whilst the amount is considerably less, there is still caffeine present in a cup of decaffeinated coffee.

Caffeine is also a diuretic meaning that it will promote you to pass urine. So you may find that if you are consuming a lot of coffee you will be running to the loo quite often and this is where sometimes replacing a cup of regular coffee for decaf can help. But please don’t assume that any urinary symptoms you may be having are simply down to your caffeine intake; please do go and see your doctor if you are suffering from any urinary problems.

Some studies suggest that caffeinated beverages may worsen gastroesophageal reflux disease (GERD) in some people. This seems to be especially true of coffee

Like a lot of addictive drugs. We can suffer from withdrawal symptoms when we are used to caffeine and suddenly stop taking it. These can include, headaches, irritability and muscle aches.

One thing I would advise against is energy drinks, especially in teenagers. Some energy drinks contain so much caffeine and sugar, it has not been unheard of for them to cause arrythmias in health individuals and I would always advise against them. 

I know that I’ve mentioned quite a lot of negatives but I do have to re-iterate that from current studies Caffeine in moderation is considered safe and one could argue that the happiness it brings to so many people, myself included, more than outweighs any potential risks but please do take into consideration any other health problems. So as with most things in life; be sensible. Use common sense and listen to what your body is trying to tell you.

That’s it for this week. If you’re enjoying the show please do subscribe or follow and leave a review and if there are any questions you would like me to answer or topics you would like me to consider for the show please do contact me via adoctorsview.uk and follow me on Instagram @adoctorsview for some behind the scenes posts.

As always, please look after yourself and please do continue to stay safe and protect everyone around you.

I’m Dr Polyvios, goodbye.