Coffee is no substitute for prolonged sleep loss. A new study just released by German scientists finds that the stimulating effects of coffee fade away after five days of habitual poor sleep. After that point drinking coffee isn’t going to help you wake up or become more alert.

If you’ve been feeling restless during the hours between midnight and morning lately you certainly aren’t alone. Reported rates of insomnia and similar sleep disruptions have skyrocketed over the past 12 months, and you don’t need a doctorate to venture a guess as to why. 2020 was a year marred by uncertainty and fear, which isn’t exactly conducive to a peaceful eight hours of rest.

Even before the coronavirus pandemic disrupted everyone’s lives, sleep hadn’t been a priority in modern culture for some time. The rise of smartphones, tablets, streaming, and social media has made it increasingly difficult for people to disconnect and unwind in the evening, often resulting in bloodshot eyes and tough mornings.

The US’ “always available” work culture probably hasn’t done our nation’s sleep habits any favors either. When you’re answering emails from your boss at 10 PM it’s not always easy to fall asleep at 11.

Countless people combat their constant fatigue with another cornerstone of modern culture: coffee. One of the world’s largest coffee companies likes to say that “America runs on” their coffee, and that may be one of the truest advertising slogans ever created.

If coffee magically disappeared off the face of the planet one random Monday morning, it’s safe to say that much of the US (and the rest of the world for that matter), wouldn’t make it out their front door anytime before noon.

Coffee is great for shaking off the cobwebs and getting moving in the morning, but these findings, put together by the Institute for Scientific Information on Coffee, should serve as a reminder to even the biggest of coffee lovers that no amount of caffeine is a suitable replacement for proper sleep.

Researchers gathered 26 volunteers and then assigned each person to either a coffee group or a placebo group. Then, for a period of five days, each person’s sleep was restricted to only five hours per night (two to three shy of the universally recommended seven to eight hours of nightly sleep). The placebo group was given decaf coffee each morning while the coffee group was given a “moderate” amount (three to five cups) of genuine caffeinated coffee.

For the first three to four days, those drinking real coffee showed improvements in their cognition, alertness, working memory, and reaction-time after their morning brew. By day five, however, all of those benefits were gone. In other words, there were no cognitive differences between the decaf and coffee groups; by day five the real coffee group may as well have been drinking water or decaf coffee.

These conclusions were reached via participants’ subjective perceptions of their sleepiness/alertness each morning, as well as through a series of cognitive tests measuring alertness, memory, etc. It’s also important to note that five days was chosen because it simulated a typical, busy five-day workweek.

“Previous research suggests that acute consumption of caffeinated coffee can reduce the impact of sleep deprivation on deficits of attention and cognitive function in a short-term setting. This study is among the first to examine whether this effect can be translated into a real-world situation, where caffeinated drinks are commonly consumed every day by people who experience chronic sleep restriction. Our study indicates that moderate coffee intake can mitigate some repercussions of reduced sleep over a few days, however, this is not a substitute for a good night’s sleep in the long term,” says study co-author Denise Lange from the Institute of Aerospace Medicine in Cologne Germany. 

Coffee is a great morning tool and makes life just a little bit easier for so many of us. These findings don’t dispute all that, but it’s also important to remember that there’s no real replacement for sleep. Coffee helps put off paying back that “sleep debt,” but at some point, all that fatigue will catch up to you.

On the subject of getting better sleep, there are no sure-fire answers. A quick internet search for insomnia remedies will return much of the same recommendations over and over again; read a book, avoid alcohol, stop looking at your computer/phone at least an hour before bed. All of these suggestions may help, but ultimately each individual must find what works for them, and there’s usually going to be a whole lot of trial and error along the way.

During a bout of insomnia, when one hasn’t slept well for a few days or more, a good night’s sleep can feel about as impossible as winning the lottery. During these times it’s important to remember that while you may not feel like you can sleep well, your body and mind absolutely can. Sometimes fixating on the need for sleep is the only thing stopping us from a deep slumber.

The full study can be found here, published in Progress in Neuro-Psychopharmacology & Biological Psychiatry.

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