“I love sleep. My life has the tendency to fall apart when I’m awake, you know?”
― Ernest Hemingway

THE BENEFITS OF SLEEP are numerous. Like eating or getting physical activity, sleep is essential for optimal health. Deep sleep is the restorative phase; we need it to feel at our best each day.

Let’s briefly look at deep sleep, the benefits of deep sleep, and the signs of insufficient deep sleep. We will begin with the stages of sleep and end with an attempt to answer the question posed by the title: How much sleep do you need?

Sleep stages

Sleep Foundation offers this take: Fall asleep, and you should cycle through three non-rapid eye movement phases of sleep, followed by one rapid eye movement (REM) sleep stage. It typically takes between 90 and 120 minutes to get through all four stages. Then the cycle begins anew.

Adults usually have four to six cycles each night. We typically spend more time in non-REM sleep; as the night progresses, we dwell in more REM-type sleep.

Adults usually have four to six cycles each night. For the first half of the evening, we typically spend more time in non-REM sleep; as the night progresses we dwell in more REM-type sleep.

• Stage 1: This drowsy stage is brief and marks the transition to sleep. Your breathing and heartbeat are slowing.
• Stage 2: Your breathing and heart rate slow even more during this stage of light sleep. Stage 2 sees a temperature drop and muscle relaxation. This stage progressively increases with each cycle throughout the night. Roughly half of our total sleep is here.
• Stage 3: This slow-wave sleep stage is the deepest cycle. Brain waves are their highest in amplitude and slowest in frequency.
• Rapid eye movement (REM): Your eyes flicker bath and forth beneath your eyelids. If we looked at your brain activity, it would not look that different from the awake you. Given much of our dreaming occurs here, it makes sense that we lose muscle tone and don’t move. Nobody wants to watch you running (in real life from that tiger you spy in your dream state.

Deep sleep — benefits

With an increase in brain sugar (glucose) metabolism during deep sleep, we support short- and long-term memory and overall learning. The pituitary gland secretes vital hormones during deep sleep, including human growth hormone.

In his 2017 book Why We Sleep, my favorite sleep expert, Dr. Matthew Walker, informs us that brain imaging (magnetic resonance imaging or MRI) illustrates this:

Slow brain waves of stage 3 sleep (deep non-REM sleep) “serve as a courier service,” transporting memories from the hippocampus [memory center] to other more permanent storage sites.

Moreover, deep sleep allows for strengthening the immune system, promoting growth and repair of tissues and bones, and more blood supply to your muscles. In addition, you get cell regeneration and energy restoration.

Deep sleep deficits

Get too little deep sleep at your peril. Sleep is associated with so many functions. Cognitive function and memory? Yes. Language learning, brain development, and motor skills. Check.

Researchers believe that deep sleep plays a role in preparing the spaces (synapses) between your nerve cells for the next day’s communication. Your brain evaluates new memories, consolidating and preserving only the most relevant ones.

Short sleep is associated with sleep disorders such as sleepwalking, night terrors, and weight gain. If you don’t enough quality sleep, you are also more likely to suffer from Alzheimer’s disease, type 2 diabetes, heart disease, and stroke.

Deep sleep — How much do we need?

Do you want to know how much deep sleep you need? First, calculate how much sleep you need overall. Most of us should try to get seven to nine hours of sleep each night. That’s the recommendation of the US National Sleep Foundation.

Now the trickier calculation: Between 13 and 23 percent of your overall sleep should be in a deep sleep; this translates to about 55 to 97 minutes each night in a deep sleep.

Sleep hygiene

So, to answer the question about how much deep sleep you need? Probably about an hour to an hour and a half each night. How can you make sure you have a good shot at achieving that? Aim for seven to nine hours of overall sleep. If you have sleep apnea, treat it — you’ll get more deep sleep, even within one day.

As we age, we tend to have less deep sleep (and more stage 2 sleep). For those of us who enjoy the occasional (and glorious) nap, we get less deep sleep at night (as our nap already contributed to our day’s allotment).

That’s it. Today we looked at one of my four pillars of health — rest. In the future, we’ll turn to the other three, including movement, nutrition, and mindfulness. Thank you for joining me today.