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How to maximise the benefits and minimise the downsides of caffeine consumption

Peter Tierney, PhD


Adam Bataineh, MD


Quick read

  • Caffeine can have a different effect on individuals
  • Caffeine has powerful, acute effects on alertness and mental performance
  • Caffeine has positive athletic performance benefits
  • Coffee intake of up to 4 cups a day is associated with reduced mortality risk
  • Caffeine has negative impacts on sleep when consumed incorrectly


Caffeine – a psychostimulant – is one of the world’s most consumed drugs. Most commonly ingested through coffee, tea, cocoa and energy drinks. 

Despite common rumour, coffee does not dehydrate you. Research has shown that drinking coffee in moderation (up to 300mg per day) provided similar hydration to water only. Larger doses can act as a diuretic – so be conscious of overconsumption.

Quick thinking

Don’t be afraid to reach for that coffee in the morning. As well as it contributing to your hydration similarly to water alone – it can have some powerful, acute effects. Coffee has been shown to help increase alertness, reduce headaches, and improve reaction time. It has also been reported to improve mood and lower mental fatigue. I would imagine all of these are feelings and improvements which a lot of people would like when starting out their day!


Coffee in the morning may also suit some people who intermittent fast – or perform early “time restricted feeding”. People report that coffee helps reduce feelings of hunger. The research is equivocal, but subjective reporting of coffee helps to suppress appetite can be useful for certain types of fasting. The suppressing of appetite from coffee ingestion could be from the volume of liquid ingested or coffee’s ingredients, and this needs to be established in future research. However, it certainly doesn’t seem to make you hungrier!

Avoiding the afternoon slump

You might find yourself reaching for a coffee to combat that tired feeling after lunch. However, caffeine too late in the day can have a negative effect on your sleep. There is evidence that strongly recommends you avoid caffeine at least 6 hours before bed time. This could be even longer as caffeine’s effect and “half-life” can be highly individualised also. If you are still desperate for a beverage, decaffeinated coffee has been shown to still provide some of the improved effects on alertness, without ingesting caffeine doses that may impact your sleep. Examples

Did you know? Decaffeination of coffee occurs when the beans are still green! The process involves swelling the coffee beans so that caffeine can be extracted. This can be done using different processes, but it’s best to aim for coffee that has been through a natural process that use only water or carbon. The beans are then dried to their normal level before being roasted.

Consider this; that dip in energy post-lunch might also be combatted through a more ‘balanced’ lunch, and / or some activity (a stroll) after you eat to control your blood glucose levels from rapid spikes and drops. Next time you feel yourself reaching for that 3pm coffee – try go for a short walk instead.

Suggested natural decaffeinated coffee brands:

The coffee night-cap

Do you ever hear people say “I can drink coffee after dinner and it doesn’t affect my sleep.” Well actually – it most likely does. Research has reported differences in subjective and objective sleep markers – meaning that people self-reported no negative effects with caffeine intake before bed, however objective analysis showed significant negative impacts on sleep. 

People underestimated the reduction in sleep quality that caffeine had when ingested 6 hours before sleep – subjectively people thought there was no significant difference in sleep quality (%) for no caffeine compared to caffeine 6 hours before bed. Objectively – their sleep efficiency worsened by almost 10% on average, from 91% to 82%.

Caffeine pre-bed has negative effects on sleep – it reduces total sleep time and sleep efficiency (how well you sleep), and also reduces slow wave sleep (deep sleep). Knowing all we know about the benefits of not only deep sleep, but getting enough good quality sleep every night, it would be responsible to avoid caffeine near bed. The effect of caffeine can be influenced by your genetics – people with two identical alleles for CYP1A2*1A are "rapid" caffeine metabolizers, meaning they break down caffeine quickly and may not feel the effect as strongly as slow metabolisers. Experiment accordingly backed with sleep data from a wearable device to determine you ideal cut-off time.

Physical performance

Caffeine has positive athletic performance benefits, and has been shown to support physical performance, particularly in endurance and aerobic events such as running and cycling. These benefits have also been shown in shorter duration, higher intensity exercise. Its performance benefits must also be weighed up with its potential negative effects, particularly for exercise and sport performed in the evening. For example, if you are a competitive athlete and train / compete in the afternoon or evening, using caffeine to support performance might be wise. Finding the balance of performance, caffeine and sleep is something to experiment with and find out what works best for you. Remember performance and sleep are intrinsically linked through recovery.

In other words, does the performance benefit you get from caffeine outweigh the negative effect it will have on your sleep and recovery that night?


Caffeine is associated with reduction in risk with overall mortality and many specific mortality risks too. It would seem prudent to not rely on caffeine for overall health, but to take health as a holistic journey. Other aspects that you might consider to help improve your health alongside caffeine include improved fitness, good nutrition, high daily activity (step count), resistance training, sufficient sleep quantity & quality, and reduced stress. These can all in unison support a reduced risk of all-cause mortality. 

Caffeine can support a healthy lifestyle, when consumed in moderation and not too late in the day to negatively impact sleep.

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November 23, 2021
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