How Does Coffee Wake You Up?
Coffee obviously has caffeine in it which upon consuming spreads quite quickly in your whole body, and reaches to even your brain. It wakes you up by blocking the adenosine receptors in your brain – more commonly known as sleep-promoting receptors. This results in you and your body becoming alert and awake.
Sip on one cup of filter coffee, which contains about 140mg caffeine, and by lunchtime, 70mg has left your system (if you made the first cup at about 7am). The average cup of coffee has around 40mg of caffeine, so after five hours, you only have 20mg left in your system. For most people, 400mg caffeine per day, which is what you get from two or four cups of coffee, is perfectly okay. The FDAs guidelines for a safe amount of daily caffeine consumption are about 400 mg, or 4-5 cups of coffee a day.
In general, most people who make a habit of drinking about 1-4 cups of coffee a day–about 400mg caffeine over 24 hours–face no apparent risk to their health.
A larger cup of coffee may contain as much as 470 milligrams of caffeine, more than the recommended caffeine intake for a day. A single cup of instant coffee contains 60-100 mg of caffeine depending on brewing strength; a cup of tea contains 30-100 mg of caffeine; and a lattes or espressos contains 90-200 mg of caffeine. An espresso has about 60-100mg of caffeine, and a cup of tea gives you a little less than 50mg. Similarly, teabag size, the amount of tea leaves, and the time it takes to steep affects how much caffeine is in your cup of joe.
| Amount of caffeine in various beverages | Safer amounts of caffeine intake |
| A cup of tea contains 30-100 mg of caffeine. | 400mg caffeine per day either intaking it from tea or coffee, is perfectly okay. |
| A latte contains 90-200 mg of caffeine. | 4-5 cups of coffee a day is considered safe and consumer face no apparent health risk. |
| An espresso has about 60-100mg of caffeine | 3-4 cups of tea a day is okay to consume for a normal person. |
Because so much variance exists among caffeinated products, it can be difficult to know exactly how much caffeine is in any given beverage, particularly in fresh-brewed cups of tea or coffee without labels. If this is the case, you might need to work out whether this is the caffeine from coffee overall, or the caffeine from coffee. If you cut coffee or tea and you are still having sleep issues, think about if you are taking caffeine unknowingly from another source.
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For example, if you were drinking a lighter-roasted coffee and switched to dark roast, you would not get nearly as much since lighter roasts have more caffeine in them compared to darker roasts. For first-time coffee drinkers who have fast metabolisms, you might not be feeling all of the effects of the caffeine. If you are new to coffee, and feel drained suddenly after drinking, you might be one of the tiny minority. It is also interesting to note that a lot of people, myself included, drink coffee regularly, not in order to enjoy the taste profile, or for general well-being induced by the caffeine, but in order to avoid withdrawal symptoms.
If you are a frequent consumer of caffeinated beverages like coffee, tea, or energy drinks, eventually your body starts producing additional adenosine receptors because yours are continually being blocked by caffeine. Even if you are a consistent coffee consumer in order to stay constantly alert, eventually your body will adjust, building up more of these receptors that house the adenosine in order to compensate for those that are blocked by the caffeine. Even if you are at a high level of adenosine, caffeine blocks all of these receptors, binding to them first.
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Caffeine blocks the neurotransmitter called adenosine, which suppresses production of the neurotransmitters norepinephrine and dopamine. By blocking the neurotransmitter adenosine, caffeine that we ingest produces opposite effects, like increased alertness associated with drinking coffee. Because caffeine in coffee has a shape that is very similar to the molecule called adenosine, caffeine can bind with the receptors of your brain, and so it blocks the Adenosine molecules from reaching the receptors of your brain. Caffeine actually does bond, since caffeine looks like adenosine receptors, but caffeine does not inhibit that cells activity since it is technically not Adenosine.
When we drink coffee, the caffeine that we ingest is bound to an adenosine receptor, since its molecules are structured like adenosine. After some time, our brains pick up what the caffeine in coffee is doing, and they build up additional receptors for receiving adenosine molecules. Caffeine looks for a particular Adenosine receptor and simulates Adenosines effects, in effect fooling your body into thinking that it is a long way off from bedtime.
This means that adenosine still has the ability to work, signaling to the brain to turn the lights on, even when caffeine is lurking around the brain. When caffeine takes over for adenosine, dopamine is allowed to slip into its place, which contributes to alertness and a positive mood.
Overall, caffeine works by changing brain chemistry, blocking adenosine, a naturally occurring sleep-inducing chemical in the brain. Coffee appears to function as a stimulant, at least partly, by blocking the binding of adenosine, the promoting sleep chemical, to its receptors. For me, so long as caffeine keeps blocking that receptor, I am going to continue brewing my magic cup of coffee each morning.
At least part of that variance comes from having its receptors in different forms. Thanks to the glancing, caffeine may be binding to the receptors in your brain, making it impossible for them to take in any of the adenosine. Caffeine and adenosine share enough of the same molecular structure that caffeine can cleave to the receptors for adenosine, but not enough to activate them. Adenosine slows down neural cell activity on nerve pathways such as these, but caffeine (which binds to the same receptors) speeds things up.
If you have had a cup of coffee, then taken a nap for no longer than 15-20 minutes, you have cleared out space on your adenosine receptors to allow the caffeine we ingested to take over. Within two hours of drinking your cup of coffee, caffeine concentrations reach peak levels in your brain, giving you a mood boost and helping your muscles feel less weighed down for a little while. The caffeine will reach its peak in around an hour, remaining at a similar level for several hours, keeping you alert when you begin work. Wait ten hours, and the caffeine will have all left your bloodstream, so you are still feeling pretty sleepy at bedtime.
If you find you are sensitive to caffeines effects, cutting back on your coffee and caffeinated teas around mid-to-late afternoon is a good idea. If you are not drinking coffee as much, or you are sensitive to caffeine, the effects can be more long-lasting — that way, you are really getting the most out of that morning latte.
You would need to drink about 10 grams of pure caffeine to achieve this caffeine content, which is difficult to handle with just coffee. The name “decaf” coffee is not quite accurate, as research from the University of Florida found that a serving of an 8-ounce cup of most decaf contains 8-14 milligrams of caffeine.
How long after a coffee can I sleep?
Caffeine may not have much of an effect on falling asleep if a person never seems to experience insomnia. Since it takes the body four to six hours to digest half of its (caffeine) intake before night, most people should refrain from caffeine during sleeping time.
Does caffeine wake you up or make you sleepy?
By interfering with specific brain chemical mechanisms that control the sleep-wake cycle, caffeine enhances alertness. However, caffeine might make people feel fatigued once the body has fully metabolized it. It depends on a person’s genetic make-up and lifestyle choices and how quickly their body metabolizes coffee.
Is 4 pm too late for coffee?
One study indicated that caffeine can impair your sleep for up to six hours after use, costing you an hour or more of lost sleep. Drinking coffee after 3 p.m. is therefore not a good idea if you want to start calming down and going to bed around 9 p.m.