This article was originally published on JamesClear.com.
Whether it is overworking or playing gadgets or watching TV programmes, modern society is getting less sleep. Most of the friends around me sleeps an average of 5-7hours on a daily basis. I myself average about 5-6 hours sleep daily. I always thought I can make up for it when it’s the weekends, but no matter how late I sleep in on Saturdays mornings I never felt fully refreshed. So this article really opened my eyes to how important that 7-8hours really is.
The Science of Good Sleep
An excerpt of the article:
Lack of Sleep: 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.
The Cost Of Sleep Deprivation
The irony of it all is that many of us are suffering from sleep deprivation so we can work more, but the drop in performance ruins any potential benefits of working additional hours.
In the United States alone, studies have estimated that sleep deprivation is costing businesses more than $100 billion each year in lost efficiency and performance.
As Gregory Belenky, Director of the Sleep and Performance Research Center at Washington State University, puts it, “Unless you’re doing work that doesn’t require much thought, you are trading time awake at the expense of performance.”
This brings us to the important question: At what point does sleep debt start accumulating? When do performance declines start adding up? According to a wide range of studies, the tipping point is usually around the seven or seven and a half-hour mark.
Generally speaking, experts agree that 95 percent of adults need to sleep seven to nine hours each night to function optimally.
To put things differently, 95 percent of adults who get less than seven hours of sleep on a routine basis will experience decreased mental and physical performance.
According to Harvard Medical School, “The average length of time Americans spend sleeping has dropped from about nine hours a night in 1910 to about seven hours today.”
And, according to Dr. Lawrence Epstein at Harvard Medical School, 20 percent of Americans (one in five) get less than six hours of sleep per night.
Most adults should be aiming for eight hours per night. Children, teenagers and older adults typically need even more.
For the full article, please read here.