If you find yourself struggling to sleep at night, you might want to carefully consider what you’ve been drinking earlier in the day. 

Whether you’re a coffee fanatic or a serial tea guzzler, the reality is that when you sip on these hot drinks, your body is getting a hearty dose of caffeine – and this caffeine can end up lingering in your system for some time. 

The effects of your morning brew can occur anywhere between 15-45 minutes after your first sip, when caffeine levels peak in your blood, according to Medical News Today. This is when you feel spritely and alert. 

The caffeine is then metabolised by the liver – and as it breaks down, you feel the effects less. Cue the urge to grab another hot bevvie from the kitchen. 

How long does caffeine stay in your system?

The average cup of coffee contains about 100mg of caffeine, while a cup of breakfast tea typically contains about 50mg of the stuff. 

Caffeine has an average half-life of about five hours, which means if you have a cup of Joe with 100mg of caffeine in it, you’ll have 50g remaining in your system after five hours, and then 25g remaining after 10 hours. 

The half-life – or how long it takes for your body to eliminate half of the original dose – really depends on how sensitive you are to caffeine, as well as other factors like whether you smoke, you’re pregnant, or are taking certain medication, etc. We know oral contraceptive use can double caffeine’s half-life, for instance. 

The Sleep Foundation explains: “For example, nicotine use can shorten the half-life of caffeine by up to 50%, so frequent smokers eliminate caffeine from their body more quickly. In contrast, people in the later stages of pregnancy metabolise caffeine more slowly.”

So really, caffeine’s half-life could be anywhere between two and 12 hours, the foundation suggests.

It’s perhaps no wonder then that experts recommend curbing caffeine intake after lunchtime in order to get a good night’s sleep. (Yup, that post-dinner espresso is probably a bad idea.)

Data from 160,000 Sleep Foundation profiles shows 88% of people who regularly consume caffeine in the afternoon have reported at least one sleep problem.

Dr Patrick Doherty, an assistant clinical professor of neurosurgery at Yale Medicine in Connecticut, previously told HuffPost: “In moderation, [there’s] nothing particularly wrong with it, but I wouldn’t have more than a cup or two of coffee a day.

“I would probably stop any coffee ingestion towards the early part of the afternoon, because having coffee within probably six hours or so of trying to go to sleep is going to disrupt [sleep].”

It’s worth bearing in mind that caffeine can also be found in cola, energy drinks, chocolate and even green tea (albeit in smaller amounts).

How much caffeine is too much?

The Mayo Clinic agrees, suggesting up to 400mg of caffeine a day (again, four cups of coffee) “appears to be safe for most healthy adults”.

Caffeine is not recommended for children, however, and the NHS advises those who are pregnant to try and limit intake to 200mg or less of caffeine per day.