Maybe your habit extends to a cup of coffee in the afternoon, or you have dinner soda.
And maybe as a result, you went to bed awake later, thinking about where you went wrong instead of falling asleep.
Rob M. van Dam, a researcher in epidemiology and nutrition at the National University of Singapore, explains when to consume caffeine wisely, what qualifies as too much, and what to know about why it affects each of us differently.
This interview has been shortened and edited for clarity.
CNN: How do we know when it’s time to stop drinking coffee during the day so we can still sleep well?
Rob van Dam: This sounds like a simple question, but unfortunately there is no single answer to it. And that’s because different people react very differently to caffeine.
If you get shivering, suddenly feel nervous, or your heart rate changes, you may be drinking too much caffeine. And in a similar way it can interfere with a good night’s sleep.
You may want to say, “Well, let’s try to reduce caffeine and not drink it after a certain time in the afternoon and see if it improves my sleep habits.” So it’s really something that everyone should experiment with for themselves – how much caffeine they drink and when they drink it.
CNN: What factors affect how we react to caffeine?
From the dam: Your lifestyle matters. For example, people who smoke metabolize caffeine in the liver about twice as fast. If you are a smoker, you will probably be able to drink caffeine until later and still be good at sleeping.
But there are other factors, such as if you use oral contraceptives as a woman, caffeine metabolism takes twice as long. You may have been able to drink caffeine in the evening and still sleep well, and then start using oral contraceptives and you may find that you can no longer sleep well.
Genetics also play a role, as some people have variations in their genetic code that affects enzymes in the liver that are metabolized and get rid of caffeine. This can make you metabolize it slower or faster.
CNN: How much caffeine is too much?
From the dam: It is generally recommended by associations such as the US Food and Drug Administration to maintain caffeine at 400 milligrams per day or less. If you look at a normal 8-ounce cup of coffee that has about 100 milligrams of caffeine, that would be up to four cups of coffee a day.
Another recommendation is to maintain no more than 200 milligrams per sitting. Although you can drink four glasses a day, you don’t want to drink four glasses at once – it will be too much for the body to metabolize, at least for most people.
CNN: Is caffeine for everyone?
From the dam: Caffeine really takes you a little and makes you even more alert. So, especially for people with routine tasks, this can be helpful. For example, if you have to drive a lot at night or if you are in the army and you are on duty to watch, but in fact nothing happens for hours.
But not everyone will need it. You may have enough energy or get enough sleep to be able to spend the day without any caffeine.
And there’s no reason to drink it if you don’t want to. Because even if you like the taste of coffee, you can always drink decaffeinated coffee and there is nothing wrong with that either.
CNN: Is Caffeine Safe?
From the dam: Recently, people have become very concerned about caffeine in relation to the risk of cancer, cardiovascular risk or other health outcomes. And research on this has actually been very encouraging. At the moment, coffee is probably one of the most studied drinks.
So if you enjoy coffee, you enjoy caffeine and you can consume it in moderation and you don’t have any harmful effects – in fact, you don’t have to worry too much about the health effects of coffee or caffeine.