If you've ever wondered why you're up all night after one coffee but your friend can drink a double espresso after dinner and fall asleep with no issue, science might just have the answer.
A physician found a person's response to caffeine is likely determined by two main genetic factors: whether their liver can metabolise caffeine quickly or slowly, and whether they carry a genetic variation that makes their central nervous system more sensitive to it.
Dr J Langer said coffee drinkers fall into one of three major groups: high, regular and low caffeine sensitivity.
"It's common for people to ask their doctor questions such as why they are kept awake by one cup of coffee, while their partner easily falls asleep after five cups," said Dr Langer. "The answer is that we are all unique coffee drinkers. Our genetic make-up programmes our reaction to caffeine, just as it programmes our hair colour and eye colour."
High sensitivity to caffeine
If you find even the slightest amounts of caffeine gives you a boost and more than one cup of coffee keeps you up all night, it's likely you have high sensitivity to caffeine.
This is likely due to slow-metabolism in the liver and 'high binding' in the central nervous system – basically it impacts the central nervous system more).
Regular sensitivity to caffeine
People with this level of sensitivity can generally drink 2-5 cups of coffee a day without sleep issues or adverse reactions.
It's thought regular sensitivity is caused by a balance between caffeine inactivation in the liver and binding in the central nervous system.
For this group, caffeine is normally not recommended in the evening.
Low sensitivity to caffeine
If you can drink coffee before bedtime and it doesn't affect your sleep, you most likely fall into this category. An individual with low sensitivity to caffeine probably will not experience the typically desired effects of caffeine throughout the day, such as wakefulness, alertness and increased concentration.
It occurs because their body metabolises caffeine quickly.In this group, higher intakes of caffeine can be consumed, although people should have no more than five cups of coffee per day for health reasons.
The research is shared in a new report authored for the Institute for Scientific Information on Coffee.