S+ by ResMed Logo

Sleep Library

The Effects of Caffeine on Sleep

However good that first cup of morning coffee tastes, the feeling that comes from drinking coffee can be even more enticing. Caffeine is a stimulant with powerful physical and mental effects. For many people, doing without caffeine, especially in the morning, is difficult to imagine. To protect healthy sleep, it's important to understand how caffeine and other stimulants affect the body, and how to manage their consumption to avoid sleep problems.

A stimulant in the body

Caffeine stimulates the body's central nervous system, creating pronounced alertness and reducing fatigue. Once ingested, caffeine takes effect quickly, within 15-20 minutes. Caffeine remains in the body for several hours. The stimulating effects of caffeine can last for as many as six or more hours. The effects of caffeine vary widely by individuals, and can be influenced by factors including body-mass index (BMI), age, medications and medical conditions. It's important to be aware of how caffeine affects your body. A mid-afternoon cup of coffee may interfere with your ability to fall asleep many hours later. Your individual sleep-wake routine also will play a role in the timing of your caffeine consumption - if you're an early-to-bed person, a three o'clock cup of coffee may upset your normal sleep regimen. To avoid caffeine disruptions to nightly sleep, work back 10 hours from bedtime to find your caffeine cut-off time.

Caffeine has multiple effects on the body that can interfere with sleep. Caffeine stimulates production of adrenaline, an alertness-boosting hormone that is linked to the body's fight or flight response. An increase in adrenaline raises heart rate and breathing, brings on a state of increased vigilance and alertness. Caffeine also blocks the effectiveness of adenosine, a chemical that helps to bring on drowsiness and to regulate sleep-wake cycles. Caffeine alters sleep architecture, the overall nightly distribution of sleep among the four different sleep stages. Caffeine in the body at night can reduce time spent in deep sleep, a phase of sleep that is critical for physical and mental rejuvenation.

Moderation is key

This doesn't mean you must stop consuming caffeine altogether. That morning cup of coffee is fine, so long as you're not having trouble sleeping at night. Many people can manage moderate caffeine consumption early in the day without compromising sleep. A general guideline is to curtail caffeine by 2 p.m. If you find yourself relying heavily on caffeine throughout the day, take a close look at your sleep. Chronic sleep deprivation and heavy caffeine consumption can go hand in hand: insufficient sleep drives up caffeine use, which leads to less sleep.

Another strategy for managing caffeine consumption to avoid sleep problems? Start the day with the most highly caffeinated beverage, and gradually taper down from there. Switch to a half-regular, half-decaf cup of coffee, or to tea, before forgoing caffeine altogether for the remainder of the day. And pay attention to size: an 8-ounce cup of coffee contains approximately 100 milligrams or more of caffeine. The amount of caffeine in popular drinks can vary widely. A latte can typically have anywhere from 60 -175 mg of caffeine, while a single-ounce espresso may have between 47-75 mg. Cola drinks usually have between 25-45 mg of caffeine, while An 8-ounce cup of green tea will typically contain between 24-45 mg of caffeine. Extra-large and supersize caffeine drinks can deliver several times these amounts of caffeine in a single sitting. Heavy caffeine consumption throughout the day is more likely to disrupt sleep.

Keep in mind that coffee isn't the only source of caffeine. Tea, cocoa, and chocolate, as well as many sodas and energy drinks, also contain caffeine. When considering your daily consumption, be sure to take these other sources into account.

Tapering down

If you decide to give up caffeine altogether, try eliminating it gradually. Giving up caffeine abruptly can lead to fatigue and sluggishness, and may cause headaches. These effects are short-term and won't cause any lasting effects to performance. Nevertheless, it can be easier and less disruptive to gradually taper down your caffeine consumption. Cut down by a cup every few days.

Other sleep-stealing stimulants

Caffeine isn't the only stimulant that can pose problems to sleep. Sugar and nicotine are two other commonly used stimulants associated with sleep difficulties. Consuming too much sugar and eating high-sugar foods too close to bedtime can interfere with sleep. High-sugar foods cause blood sugar levels to fluctuate sharply. During the day these fluctuations can lead to fatigue, which may lead to sleep problems at night. Large swings in blood sugar stimulate changes to hormone levels that may interfere with sleep at night.

Nicotine stimulates adrenaline, elevating heart rate and breathing. Smoking or chewing tobacco near bedtime can make it more difficult to fall asleep. Nicotine has been shown to reduce overall sleep time and contribute to more restless sleep. Smoking may also reduce time spent in the mentally restorative phase of REM sleep. Smoking can increase the risk of snoring and other forms of sleep disruptive breathing. Smoking creates congestion. It also irritates and inflames the tissues of the nose and throat, which make snoring more likely. Snoring causes problems for sleep by interfering with sleep quality and sleep duration.

Moderating consumption of caffeine and other stimulants is an essential part of a strong daily sleep routine, and a long-term plan for sleep health.

Back to all articles