Caffeine: How Much is Too Much?

If a caffeine kick is part of your morning ritual, you’re not alone — around 80% of us take some form of caffeine each day. In the fast-paced modern world, our reliance on caffeine has only increased. But how exactly does this potent pick-me-up impact on our health and how much caffeine is too much?

8What is caffeine?

In its pure form, caffeine is a white powder with a bitter taste. It is a psychoactive agent when ingested, meaning it affects the way the brain functions. Over the course of the day, your brain releases a neurotransmitter called adenosine, which builds up over the day and causes you to feel tired. Caffeine blocks this effect by binding to adenosine receptors in your brain, making you feel more awake and alert instead of sleepy.² 

How does caffeine affect your health?

Caffeine is absorbed rapidly in the human body, taking about 45 minutes to an hour to be completely absorbed.³ The effects of caffeine on human health have been very well studied, and though most of us consume caffeine to enhance concentration and wakefulness, it can have both positive and negative effects on many other aspects of our mental and physical health. Here are a few ways caffeine could have an impact on you:

1. Caffeine boosts athletic performance 

Because caffeine works on the nervous system, it affects how your body perceives things - like maximum muscle power and physical exhaustion. Just 100mg of caffeine (or a cup of coffee) before physical activity helps to increase endurance so that you can last longer while cycling or running before feeling fatigue.¹⁵ Taking caffeine can also change your pain thresholds so you can push your muscles harder without experiencing distress.¹⁶ 

2. Coffee and tea reduce blood pressure 

Drinking coffee and tea regularly is generally thought to help reduce high blood pressure and contribute to a lower risk of cardiovascular disease because they are rich in polyphenols.¹⁹ While people who don’t regularly drink caffeine often show increased levels of adrenaline and raised blood pressure at first, these effects don’t usually last very long. In as little as a week, regular caffeine consumers can develop a partial or even full tolerance to its adrenaline-stimulating effects and so will stop experiencing raised blood pressure when drinking tea or coffee.¹⁸ 

3. Caffeine may disturb sleep 

When it comes to sleep, people who consume caffeine close to bedtime may find it harder to nod off due to its wakefulness effect. The good news is that it’s easy to prevent caffeine from disturbing your sleep by regulating when you choose to take in caffeine. It takes about 2.5 to 4.5 hours for the average person to process half the amount of caffeine they ingest, and this half-life of caffeine changes with our lifestyles—smoking speeds up caffeine metabolism while taking oral contraceptives can slow it down.^6,7 A good rule of thumb is to stop taking caffeinated food and drinks at least 6 hours before you usually go to sleep.¹⁷ 

4. Caffeine can affect mental health 

Caffeine affects mental health and anxiety in different ways depending on how much is consumed. In low doses, it may actually help to improve mood and reduce anxiety or depression — but taking too much caffeine can make people feel jittery or tense, so it’s best to check how you’re feeling before deciding on whether another coffee is the right call.²⁰

How much caffeine is in coffee and tea?

There are many different ways someone might consume caffeine, and each source varies in how much caffeine it contains. The most popular options are coffee and tea, which are natural sources of caffeine — though each variety has a different caffeine content depending on its origin and how it is prepared. Naturally occurring caffeine is also found in cocoa beans, kola nuts, and yerba mate, while many carbonated sodas, energy drinks and even some brands of water and juice have caffeine artificially added to them.^8,9 Some painkillers also contain caffeine, since it can enhance their pain-relieving effects.¹⁰ In its pure powdered or tablet form, caffeine can be potentially dangerous as high concentrations make it far easier to over-consume. For this reason, pure caffeine isn’t recommended as a part of an average daily routine and should be cleared by your physician first.¹¹

How much caffeine should you have a day? 

There is no universal upper limit on how much caffeine is safe to take each day, and the average daily consumption of caffeine differs a lot depending on local culture and the source. The European Food Safety Authority (EFSA) advises the average adult to consume no more than 400mg of caffeine a day — around 2-4 cups of coffee, depending on their strength, or 8 cups of tea. During pregnancy, caffeine metabolism is greatly reduced, so pregnant people are advised to take just half the usual allowance of caffeine each day (~200mg). While the evidence suggests that it’s generally fine for children and teenagers to take some caffeine, they should do so cautiously so that it doesn’t negatively affect mood and sleep.¹³

In extreme cases, it is possible to overdose on caffeine. You might start to experience toxic side effects if you ingest around 1.2g of caffeine or more at once, while doses of 10-14g of caffeine are likely to be fatal. Fortunately, caffeine-related deaths are very rare, since reaching 10g of caffeine would involve drinking more than one hundred shots of espresso over a short period of time. Caffeine-related deaths do happen, but usually only when someone takes very high doses of caffeine supplements to boost athletic performance or treat psychiatric illness.¹⁴

Caffeine addiction and withdrawals - do they really exist?

You've probably met quite a few self-proclaimed coffee addicts, but is it actually possible for someone to be addicted to caffeine? Technically, yes— someone can ingest excessive caffeine to the point of harm, and feel distressed by reducing or eliminating caffeine. But caffeine doesn’t follow the same neural mechanisms that happen in other established drug abuse disorders, so some experts are wary of labelling it a dependence or addiction.^22,23 Coffee also doesn't carry the same social stigma as other stimulating drugs, so the impact of consuming a lot of coffee is unlikely to have the same social outcomes - you're probably not going to be ostracised at work for having a cup of coffee "too early" in the day. 

Caffeine withdrawal is widely recognised as a disorder, where quitting regular caffeine intake can lead to symptoms such as fatigue, headaches, depressed moods, nausea and other features similar to getting the flu. These symptoms hit their peak 1-2 days after stopping caffeine ingestion and can last up to 9 days.^{24, 25}

Do I need to avoid caffeine?

Ultimately, caffeine affects us all differently, and we all have our own tolerance to its effects depending on our genes and our lifestyles. It’s difficult to gauge how much caffeine is too much, but as long as you know your limits and avoid taking too many caffeine supplements, there’s no reason to fear that your caffeine fix is getting in the way of your health. In fact, there are many antioxidants and other compounds in coffee and tea, so drinking a few cups a day might even be good for you.²¹ Thank goodness for that!