People who rely on caffeine to keep them alert during the day might eventually notice their usual drink doesn't touch the sides anymore.Â
Dr Karan Rajan, an NHS surgeon, explained the process of why some of us eventually become immune to the perky effects of coffee or energy drinks. He said: "If caffeine makes you feel tired, it might be because of a software glitch in your caffeine gene.
"Broadly speaking, people can be fast or slow caffeine metabolisers - and it all depends on if you have the fast or slow liver enzyme CYP1A2. This enzyme influences your body sensitivity to caffeine. Depending on your metabolism, it could take anywhere from two to eight hours to remove half the caffeine."
Dr Rajan explained that caffeine keeps us alert by blocking receptors meant to catch adenosine (a molecule found in the brain that slows nerve activity). Caffeine, on the other hand, does the exact opposite and tends to keep us alert and awake.
The doctor continued: "People with a fast metabolising mutation break down caffeine more quickly, so those adenosine receptors free up more quickly. This allows the sleep-inducing chemical to bind, making you feel more tired."
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If you thought the solution was just to increase the strength of your coffee or drink more, then your body is already one step ahead of you. It turns out that our nervous system can smartly build up a tolerance to caffeine.
Dr Rajan said: "If you regularly consume lots of caffeine, and those adenosine channels are constantly blocked, then your body actually does a system update and compensates by producing even more adenosine receptors in your brain. It does this to regulate your sleep cycle so you don't glitch out."
According to the NHS, caffeine should be consumed in moderation, or you'll suffer the consequences. The compound is found in more than just coffee and energy drinks - it comes in many different forms, including teas, fizzy drinks, chocolate and some health supplements.
Downing more than 600mg a day (the equivalent of six mugs of brewed coffee) can produce anxiety, sleeplessness, agitation, palpitations, diarrhoea and restlessness. To reduce your caffeine intake, you can try drinking decaffeinated versions of your usual drinks or reducing the amount of caffeine you drink gradually.
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