How Much Black Coffee is Safe to Drink Daily? Why Coffee Can Make You Either Sleepy or Alert

The Impact of Sleep Deprivation and Caffeine on Cognitive Performance

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After work, it's time to binge-watch TV shows. You promise to watch just one episode, but end up watching countless episodes. Living in China's time zone but maintaining a U.S. schedule. When dawn breaks, you drag yourself back to the office with dark circles, relying on coffee to stay alive. But is this really sustainable?

As is well known, sleep deprivation impairs a person's cognitive processes. For instance, one's ability to concentrate diminishes, and error rates at work increase. Real-life examples of major mistakes due to sleep deprivation are not uncommon. On May 14th, a driver in Sichuan caused a collision due to fatigue, resulting in 6 deaths and 28 injuries of varying degrees.

However, sleep deprivation is not a problem that everyone can solve. According to a March 2019 report by People's Daily, over 300 million people in China have sleep disorders, with nearly 40% of adults suffering from insomnia. The "2020 China Sleep Report" directly announced that the average sleep time for Chinese people is only 6.82 hours. In situations of insufficient sleep, most people choose caffeinated beverages to stay alert. But how significant is caffeine's impact on work efficiency?

Research Findings: Caffeine's Limited Benefits

Recently, in the latest issue of the academic journal "Journal of Experimental Psychology: Learning, Memory, and Cognition," a study conducted by Michigan State University's Sleep and Learning Lab evaluated the effectiveness of caffeine in counteracting the negative cognitive effects of sleep deprivation. The results differ from what people typically imagine: caffeine can only relieve the drowsiness caused by sleep deprivation, but performance on some high-difficulty tasks remains affected.

In this study, researchers recruited 276 participants who were asked to complete a simple attention task (PVT) and a more challenging task (UNRAVEL), with tasks requiring completion in a specific order without skipping or repeating steps.

Participants were randomly assigned to either sleep at home or stay awake in the laboratory. In the morning, participants were recalled to the lab and given either a capsule containing 200mg of caffeine or a placebo capsule. After a drug absorption period, all participants were asked to complete both tasks again.

Results and Implications

Among the sleep-deprived participants, those who consumed the placebo performed poorly on both tasks. Those who took 200mg of caffeine could still perform adequately on the simpler PVT task, but when it came to the challenging UNRAVEL task, caffeine intake did not improve their performance.

The results show that caffeine can improve people's ability to stay awake and focus on a single task. However, when it comes to more complex tasks requiring higher levels of attention, the positive effects of caffeine are minimal. This also confirms that sleep is extremely important for people who need to execute high-risk procedures, such as surgeons, police officers, drivers, etc.

Although coffee as a substitute for sleep solves the problem of insufficient sleep in some ways, its effects are only temporary and limited. However, when getting more sleep is not an option, coffee remains an excellent choice.

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