If a person falls asleep easily, they can be fooled into thinking the caffeine they consumed earlier hasn’t had an impact on their ability to stay asleep, said James.
He said: “We are all different when it comes to metabolising caffeine and it is worth working out at what time you can have your last caffeine.”
As a general rule, James says people in their 30’s have their last caffeine hit six hours before bedtime and 12 hours for people in their 60’s and above.
The Sleep Health Foundation added: “Caffeine is a naturally occurring substance that affects the brain and behaviour. It can be found in many different drinks and foods.
“This includes tea, coffee, chocolate and soft drinks. Caffeine is also found in some medications. Caffeine promotes alertness by inhibiting chemicals in the brain that promote sleep.
“Caffeine is absorbed rapidly into the bloodstream and reaches peak levels within 30-70 minutes.
“Its effects can last three to seven hours, but it may take up to 24 hours to fully eliminate caffeine from the body.”