What does coffee do to your body?
Coffee is a popular energy drink, but this stimulant can have the opposite effect on some people. If you fall into this group, you might wonder: “Why does coffee make me sleepy?” The simple answer is that coffee can disrupt your sleep and affect your brain chemistry.
Read on to find out more.
The active ingredient in coffee is caffeine, though it commonly contains a broad mix of phytochemicals that affect the body. You absorb the caffeine from coffee quickly, typically reaching peak blood levels within the first 30 minutes after drinking.
Caffeine is a stimulant, which means it increases activity in your brain and makes you feel awake. Low to moderate doses give you energy and help you concentrate. For most people, coffee helps fight fatigue, but it affects everyone differently.
Coffee can make some people feel tired, though the problem isn’t just the coffee. Its effect likely reflects habits that may result in sleepiness.
How coffee affects sleep
The simplest explanation for why coffee makes you tired during the day is that it disrupts your sleep at night. Caffeine can make it hard to fall asleep, lower your total sleep time, and cause lighter, less restful sleep, in addition to other side effects.
Studies show that caffeine, when taken 3 hours before bed, causes significant sleep disruption. One study showed that even when it was taken 6 hours before bed, caffeine caused a loss of 1 hour of sleep. After a few nights, this sleep loss could significantly impair daytime functioning.
You might naturally drink more coffee to make up for the sleep loss, but your body will eventually build a tolerance to caffeine. It becomes less effective when you drink it constantly.
Studies also show that drinking coffee to fight fatigue from sleep loss makes it harder for your body to get back into a regular sleep pattern. You may inadvertently trap yourself in a vicious cycle.
Lowers melatonin levels
Melatonin is the hormone that regulates the timing of your internal sleep clock. Your melatonin levels rise in the evening in response to darkness, which helps you enter a relaxed state. Melatonin doesn’t make you sleep, but it does prime your body for rest.
Coffee, however, acts on the receptors that control melatonin release, which causes sleep problems. One small study compared the effects of regular and decaf coffee on melatonin levels and sleep quality. The results showed that, compared to decaf, regular coffee led to less overall sleep, low-quality sleep, and a longer time needed to fall.
Regular coffee also led to lower levels of melatonin throughout the night. Consequently, you should avoid drinking caffeine in the evening, especially if you already struggle to get quality sleep.
Reduced brain gland volume
Drinking lots of coffee throughout your life might also cause chronic poor sleep as you age. In one study, researchers looked at the effect of lifetime coffee drinking on healthy older people. They found that those who drank more than 3 cups of coffee daily for 20 years had reduced pineal tissue volumes in comparison to those who didn’t.
The pineal gland is the part of the brain that releases melatonin, so those with smaller pineal tissue volumes may experience lower sleep quality.
Why does coffee put me to sleep?
Coffee has different effects on people. While it can cause a lack of sleep at night, some people also feel tired shortly after drinking a cup. This may be because caffeine:
Adenosine is a brain chemical responsible for your sleep-wake cycle, wakening, and thinking. Levels rise throughout the day while you’re awake, building up in the brain: specifically, in the area of the brain that regulates your daily sleep rhythm.
High levels of adenosine block brain cell activity and make you feel drowsy. Once you fall asleep, the levels drop. Caffeine directly blocks receptors from getting adenosine, leading to higher levels in the brain. Your brain also continues making adenosine.
The longer you’re awake, the higher the adenosine levels rise, so once the caffeine wears off, you may feel tired.
Side effects of sugar
If you take sugar in your coffee, you might also experience reactive hypoglycemia (a sugar crash) after drinking a cup. A sugar crash happens when your body has a lot of sugar and responds by quickly producing insulin to keep your levels steady.
More insulin, though, causes a drop in blood sugar, which causes a sudden drop in energy. Tiredness is a common symptom of a sugar crash, sometimes accompanied by irritability, anxiety, hunger, sweating, and shakiness.
How to avoid negative side effects of coffee
The easiest way to avoid coffee-related sleep problems is to stop drinking coffee. If you don’t want to give it up, though, just try changing your habits.
Drink less coffee
Too much caffeine can interfere with sleep, and it can cause other problems like restlessness, an elevated heart rate, and anxiety. Try to abide by the recommended limit of 400 milligrams of caffeine per day: i.e, about 3 to 5 cups of coffee.
If you already drink that much and find that it causes sleep problems or makes you tired, cut back and drink water instead. You could also try decaf coffee. Decaf still has some caffeine, but considerably less. While a cup of regular coffee contains 80 to 100 milligrams of caffeine, a decaf cup only has 2 to 15 milligrams.
Avoid coffee before bed
Don’t drink coffee in the evenings, particularly less than 3 hours before bedtime.
Get better sleep
Coffee worsens sleep loss patterns. Instead of using coffee as a quick fix for exhaustion, focus on getting better sleep. If adjusting your sleep habits doesn’t help you feel more alert and rested, talk to your doctor about treatment.
Coffee can be healthy
Coffee can be a healthy drink if you have it in moderation, though it might lose its stimulating effects over time if you constantly drink it. Still, with some adjustments, you can likely continue to enjoy your morning coffee without the previously mentioned side effects.
That being said, coffee shouldn’t replace a nice, deep sleep. If you’re having trouble sleeping, talk to your doctor.
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American Academy of Sleep Medicine: "Sleep and caffeine."
Annals of Medicine: "Adenosine in sleep and wakefulness."
Harvard T.H. Chan School of Public Health: "Coffee."
Johns Hopkins Medicine: "Melatonin for Sleep: Does It Work?"
Journal of Clinical Sleep Medicine: "Caffeine Effects on Sleep Taken 0, 3, or 6 Hours before Going to Bed."
National Center for Complementary and Integrative Health: "Melatonin: What You Need to Know."
Risk Management and Healthcare Policy "Effects of caffeine on sleep quality and daytime functioning."
Sanford Health: "Sugar crash effects and how to fix them."
Sleep: "Lifetime coffee consumption, pineal gland volume, and sleep quality in late life," "Limited Efficacy of Caffeine and Recovery Costs During and Following 5 Days of Chronic Sleep Restriction."
Sleep Medicine: "The effects of coffee consumption on sleep and melatonin secretion."
U.S. Food & Drug Administration: "Spilling the Beans: How Much Caffeine is Too Much?"
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