Caffeine is a natural psychoactive substance widely used in foods and beverages across the world. Caffeine is found in many plants, including coffee beans, tea leaves, cacao pods, and kola nuts. Caffeine is also synthetically produced and used in medications and energy drinks for its energizing and alertness-promoting effects.
Caffeine is most often consumed in drinks. Since there are so many variations in caffeinated products, it can be hard to know exactly how much caffeine is in a particular drink, especially a fresh-brewed cup of tea or coffee that has no label. Generally speaking though, coffee is the most potent and most consumed caffeinated beverage. A single eight ounce cup of coffee contains between 95-200mg of caffeine. For comparison, a 12 ounce soda contains 35-45mg, about half the amount of a weaker cup of coffee.
|8 ounce cup of coffee||95 – 200mg|
|8 ounce energy drink||70 – 100mg|
|12 ounce soda||35 – 45mg|
|8 ounce cup of tea||14 – 60mg|
When we consume caffeinated drinks and foods, our stomachs and small intestines quickly absorb the caffeine. The maximum effects of caffeine usually occur between 30-60 minutes within consumption, although this timing can vary widely among individuals. After being absorbed, caffeine is efficiently distributed throughout the whole body, and it crosses the blood-brain barrier.
Inside the brain, caffeine blocks adenosine receptors. Adenosine is a sleep-promoting chemical that is produced in the brain during our waking hours. Normally, adenosine builds up in the brain the longer we’re awake. The more it builds up, the sleepier we become. When caffeine blocks this process, we remain alert and vigilant.
Research has also shown that caffeine interferes with circadian melatonin rhythms, delaying the onset of sleep if consumed close to bedtime. Circadian rhythms are physiological patterns, like our sleep-wake cycle, that operate on a 24-hour clock. They are held in check by the external cycle of day and night, and by internal cellular processes. The buildup of adenosine contributes to this process, and caffeine’s interference with this process may explain its impact on circadian rhythm.
The effects of caffeine are measured by its half-life, which typically ranges from 4-6 hours. The half-life means the time that your body has metabolized, or processed through, half the caffeine you consumed. As a result, the six-hour half-life of a caffeinated beverage you consume in the afternoon could keep you up at night.
Some factors can slow or speed up the metabolism of caffeine. Nicotine use can reduce the half-life of caffeine by up to 50%, so frequent smokers process through caffeine much quicker, with a half-life as short as two hours. By contrast, pregnant women experience slower caffeine metabolism. It is recommended that those who are pregnant or breastfeeding should avoid coffee, or limit intake to 16 ounces or less per day (about two cups of coffee).
During pregnancy, caffeine can be passed to the baby through the placenta. A trace amount of caffeine can also be found in breast milk. If you are pregnant or breastfeeding and concerned about your caffeine intake, talk to your health care provider about what steps you should take to ensure optimum health for you and your baby.
Caffeine can impact the onset of sleep and reduce sleep time, efficiency, and satisfaction levels. Older adults may also be more susceptible to caffeine-induced sleep troubles. Caffeine notably reduces the time of slow-wave sleep, which is the stage of deep, restful sleep that leaves us feeling refreshed and alert in the morning. Caffeine-interrupted sleep can lead to sleep deprivation the following day, which is characterized by fatigue and problems with learning, memory, problem-solving, and emotion regulation.
One study examined the effects of caffeine intake zero, three, and six hours before bedtime, and found that even caffeine consumed six hours before bed could reduce sleep time by one hour. In addition, study participants reported sleeping problems when consuming caffeine 0-3 hours before bed, but they did not realize their sleep was also disrupted when consuming caffeine six hours before bed. If you have difficulty sleeping, consider limiting any caffeine intake six hours before bed.
Caffeine can cause a burst of energy as it stimulates the central nervous system . Most people drink coffee in the morning to help them wake up, but caffeine consumed at night can cause more harm than good. While caffeine can boost cognitive function in the severely fatigued, it cannot permanently ward off sleep or fix the effects of long-term sleep loss. Even though caffeine can marginally boost performance, it is no substitute for a restful, restorative night of sleep.
It is also proposed that the effectiveness of caffeine varies depending on the dose and the state of the individual. For example, the arousing effects of caffeine may benefit someone who feels foggy and tired. For someone who is already alert and aroused, however, caffeine may cause over-arousal and lead to anxiety, restlessness, and dependency.
While there are short-term performance benefits to caffeine consumption, overuse can lead to insomnia symptoms or worsen pre-existing insomnia. Consuming caffeine to stay awake at night may lead to sleeplessness, anxiety, frequent nighttime awakenings, and overall poorer sleep quality.
In addition, caffeine from sodas has been linked to increased severity of sleep-disordered breathing (SDB), which is the primary characteristic of Obstructive Sleep Apnea (OSA). Notably, this association was only found with caffeinated sodas, but not with coffee or tea, although it is unclear why. Regardless, those who suffer from sleep-disordered breathing may not know about their sleep disruption and find themselves attributing excessive daytime sleepiness to other causes. If you struggle with sleepiness during the day, it might be helpful to reevaluate your caffeine consumption, especially from sodas.
Yes. It may seem counterintuitive, but some people feel like caffeine makes them tired instead of more alert. The disruptive effects of regular caffeine use on sleep can create a vicious cycle. Caffeine use causes sleep deprivation, and sleep deprivation causes sleepiness the subsequent day, which in turn causes an increased need to consume more caffeine in order to cope with the sleepiness. Even with increased caffeine consumption, sleep deprivation catches up. People may be especially aware of their long-term sleep loss after they consume caffeine because they do not experience the pick-me-up they expected, and instead feel sleepy.
Sleepiness can also be a symptom of abstinence from caffeine, which is why regular caffeine users may feel overly sleepy in the morning when they have gone all night without caffeine.
Since caffeine can be both beneficial and harmful depending on the dose, it is important to find a level of consumption that is healthy for you. The Food and Drug Administration (FDA) recommendation for safe daily caffeine consumption sits around 400mg, or 4-5 cups of coffee per day. A large cup of coffee can have up to 470 mg of caffeine content which is more than the daily recommended caffeine content. It is essential to read the fine print about what you’re drinking. Since there can be a lot of variation in the way people respond to and metabolize caffeine, talk to your doctor if you are unsure if your caffeine consumption is recommended.
The recommended cut-off time for caffeine use is a minimum of six hours before bedtime. For example, if you typically go to bed at 10pm, avoiding caffeine after 4pm can help minimize sleep problems. If you find the six-hour recommendation is not enough, make note of the times you consume caffeine and how you sleep the subsequent night. You may find you sleep better with a longer period of caffeine abstinence before bed.
Are you struggling with insomnia, headaches, or anxiety during the day? This could be a sign of caffeine overuse and dependence. Troubles during the night, like frequent awakenings, inability to fall asleep, and nighttime anxiety may also be a sign caffeine is interfering with your sleep (14). If you find yourself excessively sleepy during the day and caffeine isn’t helping, it could be a sign you are sleep deprived from extended caffeine use. In that case, it may be time to put down the coffee and catch up on some much-needed rest.
Monitoring your caffeine use is just one way you can help yourself get regular, restorative sleep. Other lifestyle choices, like a healthy diet and exercise regimen, can contribute to healthy sleep. Good sleep hygiene is comprised of all the habits and routines that optimize your sleep quality: