4.5 Hours of Deep Sleep in One Night — What Did I Do Right?

There's no question about how important sleep is — Eileen Gu's secret weapon is sleep; sleep is one of the three measures for slowing brain ageing and preventing dementia, the other two being eating less and exercising.

So what is deep sleep?

During deep sleep, your brainwaves show a distinctive signature; your heart rate, blood pressure and body temperature all drop to their lowest levels of the day, you're very hard to wake, and rapid eye movement (REM) also appears along the way. This is the stage when the most immune substances are released, and also the stage when teenagers secrete the most growth hormone, so it has a big impact on health. It also matters a lot for consolidating memory, sparking creative thinking and improving the ability to learn.

According to the China Sleep Index Report released on 19 March 2022, 28% of people get deep sleep (even 5 minutes counts). That's a very low number (I suspect it's a wristband problem — Apple Watch data generally comes out higher). Normally, deep sleep should make up 15–25% of each night's sleep. With 8 hours of sleep, normal deep sleep should be 1.2–2 hours, right?

Enough talk — here's my chart.

I actually got up at 7:20, after 6 hours 50 minutes of sleep, 60% of which was deep sleep.

As a life hacker who has been tracking my sleep for nearly two years, comparing my body's data from every angle and combining it with all kinds of scientific research, I've put together the following sleep secrets that I've tested on myself and found to work. For my friends to consider:

0. Tracking

Apple Watch, Xiaomi Mi Band, anything will do. Just like weighing yourself, tracking is where improvement begins.

Comparing my deep sleep records a year apart, the difference is pretty clear.

Here are the sleep methods I've personally tested and found effective:

1. Quit alcohol

My deep sleep after drinking is zero. Zero. Zero. The probability of this happening to me is — 100%!

Many people feel they sleep better after a drink, but that's not true. Alcohol excites the brain's nerves and makes it hard to get into deep sleep, and it also greatly suppresses how often REM sleep occurs.

2. Regularity, regularity, regularity

Some people are early-to-bed, early-to-rise types, others are late-to-bed, late-to-rise types, and modern science says both are fine. The most important thing is to always get up at the same time, get out of bed as soon as you wake up — never lie in — and only go to bed at night when you're sleepy. If you're not sleepy, don't get into bed.

Make sure you get up at the same time every morning, weekends included. A fixed sleep rhythm is very, very important, and very easy to break. Sticking to this rhythm as much as possible is the single most important thing for improving your sleep quality.

3. Find your own sleep cycle

According to the R90 sleep programme, everyone has their own sleep cycle. Mine, for example, is 1.5 hours, so I need to sleep 1.5×N hours (N being a whole number). Usually I sleep 5 cycles, which is 7.5 hours, ideally leaving a 10-minute buffer on either side. If you insisted I sleep 8 hours, I'd most likely be jolted awake out of deep sleep and feel even more tired.

Reference: Sleep (Nick Littlehales)

4. Get some sun

My smart curtains open automatically at 7am to let the sunlight in. Sunlight passes through the optic nerve to the hypothalamus, which helps synthesise melatonin, and it also stimulates the secretion of serotonin. Serotonin and melatonin are both important drivers of sleep. (Friends who take melatonin supplements — here's some for free.)

But sunlight is a major cause of ageing, so goddesses, don't overdo it. The research conclusion is to avoid the sun between 10am and 3pm as much as possible, when there's more UV.

5. Control the temperature, colour and smell of where you sleep

Keep the bedroom as dark as possible, and especially avoid blue light, because blue light affects melatonin secretion. If you really must have a small light on, orange-yellow is best;

The room should be cool, not hot and humid; the ideal temperature is 18–22°C. A drop in temperature lowers our core body temperature, which triggers the drive to sleep.

When I started tracking my sleep, I discovered by chance, almost magically, that soaking my feet in the evening directly added 0.5–1.5 hours of deep sleep. The real reason is that your body temperature rises while you soak, and when you come out into the cooler surroundings, the drop in body temperature triggers the drive to sleep.

6. Exercise, especially aerobic exercise

Exercise raises your body temperature and keeps it up for several hours; once the body cools down, the drop in temperature makes you sleepier. Exercise releases lots of hormones that dilate blood vessels and reduce anxiety; and during exercise your cells produce adenosine, one of whose main effects is to make the brain drowsy.

7. On coffee and tea

Caffeine has a half-life of 4–6 hours, so give it enough time to be metabolised. Medically, the daily caffeine intake for one person is about 400 milligrams, roughly the equivalent of two Starbucks grande Americanos.

8. NMN

I can't prove this one, but after my friends and I started taking it regularly, nights with 4 hours of deep sleep really did become more frequent.

9. Meditation

It's a way to bring on relaxation and also a good way to relieve stress. Almost every time I listen to a bedtime meditation, I fall asleep within 5 minutes...

Let me show off today's meditation record. It's from my new brain-computer-interface toy — the BrainCo meditation headband (thank you, Queen N!). I often fall asleep during meditation or sleep better afterwards... Highly recommended (this is not an ad!)

Time for bed, time for bed — I'm already past my bedtime tonight 😴