April 3, 2019
What’s Up! It’s Wednesday April 3rd!
How Much Sleep Do You Need?
By James Clear
Alright, so sleep is important, but 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 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.
The Cost of Sleep Deprivation
The irony of it all is that many of us are suffering from sleep deprivation so that 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 over $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.”
And 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 7 or 7.5 hour mark. Generally speaking, experts agree that 95 percent of adults need to sleep 7 to 9 hours each night to function optimally. Most adults should be aiming for eight hours per night. Children, teenagers, and older adults typically need even more.
Here's a useful analogy for why sleep is so important.
The Theory of Cumulative Stress
Imagine that your health and energy are a bucket of water. In your day-to-day life, there are things that fill your bucket up. Sleep is one of the main inputs. These are also things like nutrition, meditation, stretching, laughter, and other forms of recovery.
There are also forces that drain the water from your bucket. These are outputs like lifting weights or running, stress from work or school, relationship problems, or other forms of stress and anxiety.
The forces that drain your bucket aren't all negative, of course. To live a productive life, it can be important to have some of those things flowing out of your bucket. Working hard in the gym, at school, or at the office allows you to produce something of value. But even positive outputs are still outputs and they drain your energy accordingly.
These outputs are cumulative. Even a little leak can result in significant water loss over time.
Keeping Your Bucket Full
If you want to keep your bucket full, you have two options.
Refill your bucket on a regular basis. That means making time for sleep and recovery.
Let the stressors in your life accumulate and drain your bucket. Once you hit empty, your body will force you to rest through injury and illness.
Recovery is not negotiable. You can either make time to rest and rejuvenate now or make time to be sick and injured later. Keep your bucket full.
Ok, But Can You Catch Up on Sleep?
Extra sleep can remedy some of the negative effects of several bad nights of sleep. New research found that catching up on sleep on the weekends brought daytime sleepiness and inflammation levels back to baseline; however, cognitive performance did NOT rebound.
What exactly does that mean? If you're not getting enough sleep during the week, you cannot depend on catch-up sleep on the weekends to restore your focus and attention. The only way to keep levels of those performance measures high is to make sure you're getting adequate sleep every night.
Now does this mean you shouldn't even try to catch up on sleep? No. If you're already sleep deprived, you should definitely try to get some extra sleep. But the best thing to do, both for immediate performance and for the long-term, is to prioritize sleep every night—not just on the weekends.