If you main line a cup of joe when you wake up, you’re not alone. In fact, it’s perfectly okay — and probably even healthy: Research has shown that, for most people, a moderate caffeine intake is linked to a lower risk of several diseases including type 2 diabetes, heart disease, and liver and endometrial cancers.
However, if you’re taking in a morning brew (or two), lunchtime java, and an afternoon cappuccino, it’s important to realize the effect that caffeine has on your sleep.
First, quick recap of how sleep works: Your 24-hour circadian rhythm is the primary factor that determines your sleep and wake cycle. Alongside your circadian rhythm is a complementary sleep pressure system in your brain. This system, unfortunately, is especially susceptible to being disrupted by caffeine.
If you want to keep your sleep cycles on track, keep reading to understand how your genes, gender, diet, and dosage all impact how your body processes caffeine.
| Member Tip: With Oura’s new Experiments feature, members can test and learn more about how late-afternoon caffeine affects their sleep and recovery. When you complete an experiment, you’ll receive an Experiment Report with the results of how your scores or contributors were affected. |
How Caffeine Works
Caffeine tricks your brain into thinking it’s not tired by blocking your sleepiness signal, adenosine. Adenosine is a brain molecule (neurotransmitter) that helps register elapsed time.
The longer you are awake, the more adenosine will accumulate in your brain, creating pressure to sleep. Sleep wipes the slate, resetting your adenosine levels.
Caffeine has a unique ability to disrupt this signal by transitioning from your blood into your brain—crossing a difficult border known as the blood-brain barrier.
Without caffeine, adenosine binds to receptors that send sleepiness signals throughout your body. However, if caffeine enters the brain, it fits in the same receptors and blocks adenosine from binding.
When adenosine receptors can’t fire, your brain falsely registers that it has been awake for a shorter period of time, making you feel more alert.
When caffeine leaves your system you experience a crash because all your adenosine has been building up and binds all at once. This experience can vary by person, as caffeine is cleared from your system at different rates.
RELATED: Why Am I Tired in the Afternoon?
How Long Does Caffeine Stay In Your System?
Caffeine has a half-life of 5 to 7 hours, which means it takes that many hours to break down half of the caffeine in your system.
For example, if you have a cup of coffee at 3pm, by 8pm you have only metabolized half of that caffeine — the other half is still in your system
However, half the population may have a gene that leads to slower processing of caffeine, meaning the half-life is even longer. Caffeine is metabolized by a particular enzyme in your liver, determined by your genes. Fifty percent of the population may have a variant in this gene — CYP1A2 — that makes them a slow vs. fast metabolizer. You can often find this data through one of the many direct-to-consumer genetic testing companies (e.g, 23andMe).
Other factors, such as hormones, may also impact how you break down caffeine. Women using hormonal birth control, for example, have an extended half life for caffeine, meaning it stays in their system for much longer.
Because of all of these factors, there’s no cut-and-dried time to stop consuming caffeine. However, experts typically recommend cutting out caffeine by 2 pm, if not earlier. And don’t have too much, no matter how early in the day. The National Sleep Foundation recommends less than 240 milligrams per day, which can easily be met with just two regular cups of coffee!
READ MORE: Why Do I Wake Up Tired? How to Feel More Alert in the Morning
Tracking Caffeine in Your Oura App
When caffeine is in your system, it activates your nervous system and increases your resting heart rate (RHR). This can interfere with your ability to wind down before bed and may be evident in your RHR pattern as you sleep.
Remember to Tag caffeine in your Oura App, and watch for these other patterns in your Oura metrics on nights when you think caffeine might still be in your system:
- higher average RHR throughout
- delay in RHR reaching its lowest point
- higher restlessness
- increased time spent awake
Keep in mind that soda, tea, medication, and even chocolate can contain enough caffeine to disrupt your sleep.
References
- Patwardhan, Rashmi V., Paul V. Desmond, Raymond F. Johnson, and Steven Schenker. “Impaired elimination of caffeine by oral contraceptive steroids.” The Journal of laboratory and clinical medicine 95, no. 4 (1980): 603-608. (link)
- Ribeiro-Alves, M. A., Trugo, L. C., & Donangelo, C. M. (2003). Use of oral contraceptives blunts the calciuric effect of caffeine in young adult women. The Journal of nutrition, 133(2), 393-398.
- Walker, M. (2017). Why we sleep: Unlocking the power of sleep and dreams. Simon and Schuster.
- Yang, A., Palmer, A. A., & de Wit, H. (2010). Genetics of caffeine consumption and responses to caffeine. Psychopharmacology, 211(3), 245-257.
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Cornelis, M. C., El-Sohemy, A., Kabagambe, E. K., & Campos, H. (2006). Coffee, CYP1A2 genotype, and risk of myocardial infarction. Jama, 295(10), 1135-1141.