Siffre was a French scientist and a pioneer in chronobiology, which is the study of biological rhythms. The most well-known of these biological rhythms is the circadian rhythm, which controls the human sleep-wake cycle, and Siffre was on a mission to learn how, exactly, it worked.
Siffre’s life in the cave was spartan at best. He lived in a tent that sat on a small wooden platform with a bed, a table, a chair, and a phone that he could use to call his research team above ground. His underground home was equipped with a single lightbulb, which provided a soft glow to the piles of frozen food and 800 gallons of water nearby. There were no clocks or calendars, no way for him to discover what time it was or whether it was day or night. And this was how he lived, alone, for six months.
Within a few days, Siffre’s biological clock began to take over. He would later recall his experiments by writing, “My sleep was perfect! My body chose by itself when to sleep and when to eat. That’s very important. We showed that my sleep-wake cycle was not twenty-four hours, like people have on the surface of the earth, but slightly longer—about twenty-four hours and thirty minutes.”  On several occasions, Siffre’s body transitioned to a 48-hour sleep-wake cycle where he would stay awake naturally for 36 hours and then sleep for 12 hours.
Siffre’s work, along with the experiments of a handful of other researchers, helped kickstart a scientific interest in sleep that has resulted in sleep performance centers at major universities like Harvard and the University of Pennsylvania. Given that we spend almost 1/3 of our lives sleeping, it’s hard to believe the topic has only gained a large scientific following in recent years.
In this article, I’ll share the science of sleep and how it works, discuss why many people suffer from sleep deprivation without knowing it, and offer practical tips for getting better sleep and having more energy.
How Much Sleep Do You Need?
How much sleep do you really need? To answer that question, let’s consider an experiment conducted by researchers at the University of Pennsylvania and Washington State University.The researchers began the experiment by gathering 48 healthy men and women who had been averaging seven to eight hours of sleep per night. Then, they split these subjects into four groups. The first group drew the short straw. They had to stay up for 3 days straight without sleeping. The second group slept for 4 hours per night. The third group slept for 6 hours per night. And the fourth group slept for 8 hours per night. In these final three groups — 4, 6, and 8 hours of sleep — the subjects were held to these sleep patterns for two weeks straight. Throughout the experiment the subjects were tested on their physical and mental performance.
Here’s what happened…
The subjects who were allowed a full 8 hours of sleep displayed no cognitive decreases, attention lapses, or motor skill declines during the 14-day study. Meanwhile, the groups who received 4 hours and 6 hours of sleep steadily declined with each passing day. The four-hour group performed worst, but the six-hour group didn’t fare much better. In particular, there were two notable findings.
First, sleep debt is a cumulative issue. In the words of the researchers, sleep debt “has a neurobiological cost which accumulates over time.” After one week, 25 percent of the six-hour group was falling asleep at random times throughout the day. After two weeks, the six-hour group had performance deficits that were the same as if they had stayed up for two days straight. Let me repeat that: if you get 6 hours of sleep per night for two weeks straight, your mental and physical performance declines to the same level as if you had stayed awake for 48 hours straight.
Second, participants didn’t notice their own performance declines. When participants graded themselves, they believed that their performance declined for a few days and then tapered off. In reality, they were continuing to get worse with each day. In other words, we are poor judges of our own performance decreases even as we are going through them. In the real world, well-lit office spaces, social conversations, caffeine, and a variety of other factors can make you feel fully awake even though your actual performance is sub-optimal. You might think that your performance is staying the same even on low amounts of sleep, but it’s not. And even if you are happy with your sleep-deprived performance levels, you’re not performing optimally.