Too much caffeine can lead to chronic sleep deprivation

Adenosine is a chemical that helps regulate sleep. Throughout the day, adenosine levels rise steadily, which then makes you want to sleep later in the evening. Then, at night when you're asleep, your brain is cleared of adenosine, which helps you wake up in the morning. Caffeine helps you feel more stimulated and awake by blocking adenosine receptors in the brain.

Although a cup of coffee every now and then may not be harmful, combining too much caffeine with a limited amount of sleep can have health consequences.

When you don't get enough sleep at night, adenosine remains in your brain. Drinking coffee or something else with caffeine may temporarily block the increased adenosine levels, but it will not completely eliminate the chemical.

Over time, if you continue to use caffeine to stay awake rather than getting a good night's sleep, your adenosine levels will continue to rise and lead to persistent sleepiness, fatigue, and impaired cognitive function.

A lack of sleep can also exacerbate pre-existing mental health conditions, such as depression and anxiety, and can cause people who previously had no mental health problems to become angrier and more impulsive. In a study of young adults who were deprived of sleep for five days, participants had increased responses to angry faces in their amygdala, the part of the brain that processes fear and danger, compared to their baseline.

"The simple truth is that you cannot keep yourself propped up with caffeine indefinitely because the rising tide of adenosine in your brain will become impossible to ignore," Friedman writes.

How to break the caffeine cycle

According to Friedman, many people have a hard time falling or staying asleep or end up waking up too early. Currently, a third of Americans say that they don't get enough sleep at night to feel rested and restored in the morning.

To reduce your reliance on caffeine to stay awake, Friedman recommends drinking caffeine in the morning rather than the afternoon. In addition, if you metabolize caffeine slowly, it might be better to drink tea rather than coffee in the morning.

Although it may be tempting to turn to medications such as Ambien and Lunesta when you can't sleep at night, taking them too often can be habit-forming and addictive. They can also have negative impacts on learning and memory, particularly among older adults.

Instead of using medications to fall asleep, Friedman suggests changing your habits so that your brain associates your bed only with sleeping rather than other activities that might keep you awake.

"Set a regular time for sleep. If you're not asleep in 15 or 20 minutes, get out of bed and go to a comfortable chair or couch and read or watch something that's not too exciting," Friedman writes. "As soon as you feel tired, go back to bed and try again. Not asleep in 20 minutes? Repeat this drill until you are."

Although you may spend the first few nights getting in and out of bed, the amount of time that you're asleep while in bed will be much higher. "You will be on your way to breaking the learned association between your bed and insomnia," Friedman writes. (Friedman, Washington Post, 5/30)

Multiple studies suggest a variety of benefits are associated with hitting the sleep "sweet spot," but how long is just right for most people? Writing for the New York Times, Jane Brody shares the sleep target people should aim for — and offers six expert tips to get a better night's sleep.