How does caffeine work and is there a best time to drink it?

How does caffeine work and is there a best time to drink it?
  • PublishedSeptember 14, 2023

What chemical can act as a pesticide, help premature babies to breathe properly, enhance sport performance and also give you a buzz?

You guessed it: one of our favourite everyday psychoactive drugs, caffeine.

We explore the workings of this popular chemical and ask how much is too much?

And also ponder important questions like whether you can get more ‘bang for your cup’ if you drink your coffee later in the morning, and what happens if you eat a piece of chocolate with it?

What is caffeine?

Caffeine evolved in plants as a chemical defence, says Ian Musgrave, a molecular pharmacologist from the University of Adelaide.

Not only can the chemical paralyse and kill insects that chomp on caffeine-containing leaves and berries, but in smaller doses, caffeine in the nectar of flowers has been found to help bees remember where to come back to.

“It’s the dose that makes the poison,” Dr Musgrave says.

Graphic of  molecular structure of caffeine
Caffeine is a fat-soluble chemical that quickly enters the central nervous system.(Getty Images: Dr_Microbe)

It’s in those smaller doses that caffeine appears to be incredibly useful to humans – not just in giving us a pleasurable daily boost, but as a medical treatment.

“It’s such a versatile molecule,” says Treasure McGuire, a pharmacologist at Mater Health and Bond University.

“It has a wide array of pharmacological effects.”

For example, she says, a caffeine mixture can help with asthma and is used in neonatal nurseries as a bronchodilator, which help widen air passages in the lungs.

“It’s one of the drugs that allows premature babies to breathe.”

So how does it work in the body?

Caffeine quickly enters the central nervous system and binds to receptors involved in the release of the feel-good hormone, dopamine, in the brain. 

“It stimulates the pleasure and reward centre in the brain,” Dr McGuire says.

Caffeine is also a stimulant that makes us more alert and focused. As well as opening up our airways, it increases our metabolism, heart rate and blood pressure.

For all these reasons, caffeine – even in the form of a single cup of coffee — is also used as a performance-enhancing drug in sport.

Friends drinking coffee together laughing
Coffee is a great social drug as it stimulates our brain’s pleasure centre.(Getty Images: Betsie Van der Meer)

It enables athletes to train harder and cope better during performance, says Evangeline Mantzioris, a nutritionist and sports dietitian at the University of South Australia.

“It reduces the perceived effort you are putting into work,” she says.

But back to ordinary folk: what do we do to get the most out of a morning coffee?

When is the best time to have your first coffee?

It’s widely believed that delaying your morning coffee until around 90 to 120 minutes after you wake up is a good idea.

The reasoning is that cortisol, a hormone that helps stimulate you in the early morning, rises in the early morning but falls off as the morning goes on.

“The theory is cortisol carries you through that initial couple of hours after you wake up,” Dr Mantzioris says.

And so the perfect time to have a coffee is mid-morning, once your cortisol levels have dropped off.

Caffeine also interacts with a chemical called adenosine, which is involved in energy production.

Adenosine can trigger a process that makes us drowsy when it binds to cells in our bodies – and this may be more likely to happen later in the morning.

Caffeine can stop this binding process, so it may be best to delay your coffee until you start to get that sleepy feeling.

But Dr McGuire says there are many factors that can determine whether drinking at a particular time of day makes a difference.

“For some people it will make no difference at all and for others it may be helpful.”

And apart from fitting in with body clocks, the best time for coffee may well be determined by the benefit you feel you get by drinking it.

Beyond staying awake, we might prefer to drink coffee to focus on work, as a social ritual with others, or as a pick-me-up after lunch.

How late in the day should you drink coffee?

Dr Musgrave is “not overly convinced” by data suggesting there is a best time of the day to drink coffee, although drinking it too close to bedtime could be a problem.

But again – there’s no hard and fast rules.

“Some people metabolise it very rapidly, some people metabolise it very slowly,” Dr Musgrave says.

So that’s why some people can drink it late in the day without it affecting their sleep, but others can’t.

Coffee in different sized cups
How much coffee you can drink without it affecting your sleep will depend on many things, including how fast you metabolise caffeine.(Getty Images: vitpho)

Another thing that will determine how much coffee you can drink and how late in the day is how much practice you’ve had drinking it.

Your body can become habituated if you drink regularly, and you will need more coffee to get the same fix.

In fact, that’s why regular coffee drinkers can experience withdrawal symptoms and cravings when they suddenly stop drinking it.

From caffeine to carbs: have you ever wondered about the science behind what you eat? Get in touch if you have a question you’d like us to unpack.

How much is too much?

If you have too much caffeine for your body to handle, you can get symptoms such as dizziness, palpitations, anxiety, irritability, tremors, sleeplessness – and worse, including seizures, if you overdose.

But exactly how much is too much for you personally, will depend on how well you metabolise caffeine and how tolerant your body is to it.

The food authority, FSANZ, has recommendations on the maximum daily caffeine intake.

Man reaches for cans of drink in the fridge
When working out how much caffeine you’ve had, don’t forget cola and energy drinks, including those containing guarana.(Getty Images: Stockah)

For an adult, this might be two or three espressos but the exact amount of caffeine in the cup is hard to work out given it varies with blend, brewing methods and of course, what size cup you use.

FSANZ advises pregnant women and children consume less caffeine and reports evidence that children consuming around two cans of cola a day can have increased levels of anxiety.

Cup of tea with teabag from above
Tea contains a large amount of tannins that slow the absorption of caffeine but still contributes to your total caffeine intake.(Getty Images: Karl Tapales)

And caffeine from other sources like tea, chocolate, soft drinks (including energy drinks that contain guarana) needs to be counted too.

Caffeine is also present in a range of pharmaceuticals and, more recently, even in vapes.

“It’s hard to kill yourself from normal consumption of coffee, but if you vape and take energy drinks and a caffeine tablet you may very well get into the toxic regions and get really sick and possibly die,” Dr Musgrave says.

Is caffeine good for your health?

There’s nothing quite like chocolate to go with your coffee.

They both contain caffeine so having them both together can add to the buzz – not to mention the effect of the added sugar.

“Your brain is saying ‘I’m experiencing one pleasure, I want to augment that,” Dr McGuire says.

But there’s also some suggestion the combination may have health benefits.

For example, research has found drinking French press or Turkish coffee with dark chocolate leads to greater absorption of antioxidants in both, than when both are consumed separately.

But as to whether this really translates to better health will depend on someone’s whole dietary pattern, Dr Mantzioris says. The same goes for any link between coffee and weight loss.

In general the evidence linking coffee with appetite control is equivocal.

“Caffeine increases metabolism but none of the weight loss products with coffee extract actually work,” Dr Musgrave says.

And associations between coffee drinking and lower rates of diseases like Parkinsons and Alzheimers’ disease are equally fraught.

The question is whether the beneficial effect is due the coffee or something else entirely, Dr Musgrave points out. 

“It might be that people who drink coffee are more likely to walk down to the local coffee shop.”


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