by Dave Asprey
The more time you spend in either REM or delta sleep, the more restorative your sleep will be. That means you can spend less time asleep and wake up more refreshed, younger, and smarter. You know, Super Human.
HEART RATE VARIABILITY (HRV)
Your autonomic nervous system regulates bodily functions such as metabolism, breathing, and sleep. It is made up of two systems: your sympathetic nervous system and your parasympathetic nervous system. The former is responsible for your stress response—it initiates your highly stimulating fight-or-flight response in the face of a stressor. The parasympathetic branch activates activities associated with rest and recovery such as sexual function and digestion.
When your sympathetic nervous system is activated, your heart rate becomes very even no matter how fast it beats. This is a sign of a stressed animal. But when your parasympathetic nervous system is in charge, there is a greater variability between heartbeats. In other words, you may have the same number of beats per minute, but they are less rhythmic when you are relaxed. You are able to recover from stress more quickly, and this is reflected in a quick acceleration and then deceleration of the heart rate. Your heart rate variability (HRV) is the measure of this variability between heartbeats. Low HRV is associated with anxiety disorders and even cardiovascular disease, while high HRV is linked to cardiac resilience and overall heart health.
There is also a direct relationship between HRV and sleep. When you do not get adequate quality sleep, your body becomes stressed and the sympathetic nervous system is activated. This reduces HRV. One study from the University of Pennsylvania found that just five nights of sleep restriction significantly reduced participants’ HRV.19 In contrast, consciously increasing your HRV during the day improves your sleep efficiency.20
Here’s the bad news. Lots of things, including the aging process, lower your HRV. Being out of shape, overtraining, chronic stress at work or home, inflammation, and infections all reduce HRV. The good news is that even if you don’t measure your HRV, you can usually increase it by meditating, doing breathing exercises, taking a hot bath, sleeping better, eating better, consuming fewer toxins (including alcohol), and even taking the right supplements for your biology. I often find type A personalities—executives who also want to be endurance athletes—have the HRV of very old people. When they actually see the results, they realize that burning the candle at both ends isn’t serving them.
When you decide to track your HRV, you are effectively measuring how stressed you are on a physiological level. This is incredibly valuable information. You already know that stress from all sources accelerates aging. So when you know your body is stressed, you must choose to actively recover rather than burdening your system even more. This alone can dramatically alter the course of your aging.
TRACKING DEVICES
We have come a long way since the early days of 1970s clip-on pedometers, home bathroom scales, and even the old Basis tracker I worked on. The new sleep tracking devices are sleeker, more attractive, and more accurate, and measure everything from your HRV to specific sleep states and even brain waves. Some can help you wake up more gently so you are not jarred out of sleep and forced to start your day in a state of physiological stress.
Unfortunately, most of the wristband devices that claim to track your sleep don’t gather particularly great sleep data because they were designed to track movements, not sleep. When the industry realized there is little value in movement data, they tried to add sleep functionality. It’s not really their fault; it’s been this way since the 1970s. We’ve all heard the “ten thousand steps per day” metric, but did you know there is no science behind this? In 1965, a Japanese company, Yamasa Tokei Keiki, created a clip-on pedometer designed to get people to walk ten thousand steps per day and simply made this number up.
This is why your best options to track your sleep are either a simple, inexpensive app on your phone or an unobtrusive high-tech ring. There are plenty of options in between, with a wide range of data. Your mileage may vary. If you already have a device, you can likely use its limited sleep tracking to see if you can improve your sleep, but most devices don’t provide a great window into how much deep sleep you’re really getting, and even fewer show precious HRV data.
No matter which sleep tracker you choose, the important thing is to gain a sense of how well you are sleeping and then begin paying attention to the factors that influence the quality of your sleep. You can make smarter choices about how to spend your energy the next day when you know how much savings you have in your recovery bank. To start that process, I recommend the following technologies.
SLEEP CYCLE APP
The Sleep Cycle app has the highest return on investment for sleep tracking, but not because it gives you great data. It doesn’t. The ROI is high simply because it doesn’t cost anything except the time you spend to set an alarm clock you already use! It is a simple, inexpensive option to roughly track your approximate sleep cycles using only your phone’s microphone and a movement sensor. It analyzes breathing and movements to determine when you’re awake, in deep sleep, or in REM sleep. It will (embarrassingly) record your snoring and graph how many minutes you snore per night. Best of all, its alarm feature makes sure not to interrupt your deep sleep. You tell the app when you want to wake up, and then you place your phone (always in airplane mode) next to your bed or on your nightstand when you hit the sack. When you’re in a light sleep phase around your programmed wake-up time, your alarm will go off. This way, you still get to complete your cycle of deep sleep and you’re not as tempted to hit the snooze button. Sadly, there is no measure of heart rate variability, and the sleep data is not highly accurate.
I have used this app for more than five years almost every single night because the alarm never jolts me from delta sleep, and I like the snoring reporting!
COST: Free, or $29.99 per year for Premium
PLATFORMS: iOS, Android
MEASURES:
Intelligent wake-up
Sleep analysis
Nightly sleep graph
Alarm melodies
Snooze
Apple Health integration (iPhone only)
Database export (iPhone only)
OURA RING
The Oura Ring is my number one sleep tracking device recommendation. While it isn’t the cheapest, it’s not the most expensive, either. It does provide the very best data of any sleep technology and is easy to use. With a full range of metrics and advanced analyses, the Oura helps you see what’s happening under the hood while you’re sleeping. The more data you can track, the more insight you have, and the easier it is to make small changes that will help you get the best rest in the least time. The Oura Ring is also one of the most attractive wearable devices out there. It’s sleek and modern and looks like a regular ring, not a clunky tracking device.
The Oura offers a unique feedback feature that analyzes your data to calculate a Readiness Score—an assessment meant to help you understand whether you’re ready for a hard-charging day ahead or if you should focus on rest and recovery. The Readiness Score uses information from your sleep the night before, your activity the day before, and a handful of other measures to help you make informed decisions about how you should plan your day.
This ring also tracks your average body temperature throughout the night, which can help you understand if tweaking the temperature in your bedroom will improve your sleep. My data shows that, indeed, a cooler room equals more REM sleep. Information about body temperature is also useful for women who are tracking their menstrual cycles. You can expect to see a bump of about 0.3 degrees right around the middle of your menstrual cycle when your progesterone levels rise during ovulation. This is valuable information for women who want to take control of their biology.
The Oura is one of the few trackers that provide your HRV and respiratory rate. These are good indicators of how stressed you are and therefore how quickly you are aging. As you begin to follow the recommendations in this book, you can che
ck in on these measures to see how they change. I genuinely enjoy looking at my Oura score in the morning to see how well I did (or didn’t do) the night before. It is my most trusted, useful sleep tracker and overall biomonitor, and it tracks exercise information, too.
COST: $299 (for the basic model)
PLATFORMS: iOS, Android
MEASURES:
Total sleep
Sleep efficiency
REM sleep
Deep sleep
Light sleep
Latency (time from pillow to falling asleep)
Timing
Body temperature
Heart rate variability
Respiratory rate
Calorie burn
Steps
(Disclosure: After completing the first draft of this book, I joined Oura’s advisory board and became a small investor in my favorite sleep app because it’s the best I’ve used.)
After tracking my sleep for about two decades, I have learned to correlate how I feel with the quality of my sleep. When I wake up, I always guess what my Oura Ring score is based on how I’m feeling. And I’ve found that over time those guesses have gotten closer and closer to the Oura Ring results because I’ve learned to detect precisely how it feels to get a night of good quality sleep—and how it feels when I don’t. I can also use this information to test new sleep hacks and see which gives the best return on investment. When I make a tweak to my sleep schedule, I track how those differences stack up.
This has allowed me to fine-tune my protocols to the point where I can travel multiple times a week and no longer have to deal with jet lag. This is an art and a science because everyone’s biology reacts to different inputs in unique ways. For instance, you might not be as sensitive to blue light as the next person, or you might be extremely sensitive to blue light. The point is that you don’t always know what’s killing you until it’s too late. Mastering your sleep is an important way to eliminate some of the cuts that are aging you and take control of your biology.
SLEEP BETTER, NOT MORE
Tracking your sleep is only half of the equation. You can have the best, most accurate data in the word, but if you don’t do anything with it, it’s worthless. Taking action is equally important. The following hacks range from the extremely simple to somewhat complex, and from free to moderately expensive. Choose those that are best for you to make sure you are getting the greatest possible return on your sleep investment.
DIRECTLY DIAL IN YOUR SLEEP STATE
Since delta (slow) waves are so good for the brain, scientists have found ways to create more of them during sleep. In one study, transcranial magnetic stimulation (TMS)—which uses magnetic fields to stimulate parts of the brain—triggered the release of slow waves that spread to the rest of the brain,21 but that’s not an option for most people on a nightly basis. Fortunately, there is an easier way to increase delta waves. In a 2010 study, researchers experimented with sound and found that short auditory tones—50 milliseconds each played at a rate that mimicked the natural changes in brain neurons during sleep—increased slow waves by nearly 50 percent during non-REM sleep.22 Other studies found similar results.23
Fortunately, there’s an app for that! It’s called Sonic Sleep Coach, created by Daniel Gartenberg, PhD, who has been awarded more than $1 million in NIH grants to study sleep. Sonic Sleep Coach uses your smartphone’s microphone to sense your breathing while you sleep, which indicates when you’re in deep or REM sleep. It plays specific sounds to increase REM when you’re already dreaming and different sounds to increase deep sleep. The result is a meaningful improvement in your sleep efficiency. If it picks up on noise, it even plays audio tones to block out city sounds so your sleep isn’t disturbed. I always use Sonic Sleep Coach when I’m on the road, and sometimes at home.
(Disclosure: After writing this, I became an advisor and a very small investor in this impressive app because I believe in improving sleep, and it works!)
REDUCE BLUE LIGHT
Other than a cup of coffee right before bed, nothing is more like kryptonite for your sleep than bright blue or white light in the evening. It truly makes you old in several different ways. Blue light is everywhere—we get normal amounts from the sun, but we get large, unbalanced doses from light-emitting diodes (LEDs) used in energy-efficient bulbs and to illuminate the screens on TVs, computers, tablets, and smartphones. Blue light has a short wavelength, so it produces more energy than light frequencies with a longer wavelength, like red light. The odds are high you’ve heard some of this already but dismissed how big of a problem it is on your path to becoming Super Human. The data is convincing, and it’s easier than you think to transform blue light into only a minor problem.
Blue light is not all bad. Exposure to blue light during the day wakes you up, makes you more alert, and can even improve your mood. White- or blue-light emitting goggles and panels are used to treat a number of issues such as seasonal affective disorder (SAD), jet lag, and premenstrual syndrome.24 The problem is that newer artificial lights like LEDs and compact fluorescent light (CFL) bulbs don’t contain most of the infrared, violet, and red light that’s found in sunlight. Instead, they increase the intensity of blue light to a level that our eyes, brains, and bodies haven’t evolved to handle. This is what I call “junk light” because it’s just as unhealthy and aging as junk food.
You’re bombarded with junk light throughout the day and for much of the night—when you’re on your phone, working at your computer, or watching TV—and all this blue light exposure messes with your sleep.25 Blue light shifts your circadian rhythm in part by suppressing melatonin, the hormone that tells your brain when it’s time to sleep. This tricks your body into thinking it’s daytime 24/7.
Normally, the pineal gland, a pea-sized gland in the brain, starts releasing melatonin a couple of hours before it’s time to go to bed. But blue light can mess with this process by stimulating a type of light sensor called intrinsically photosensitive retinal ganglion cells (ipRGCs) in the retina of the eye. These sensors send light information to the circadian clock, telling the body when it’s time to sleep and wake up using more than just melatonin.26
When light sensors are stimulated by blue light at night, you have a harder time falling asleep. A 2014 study found that people who read from a light-emitting device before bed took longer to fall asleep, slept less deeply, and were more alert than people who read a printed book.27
The amount of blue light you’re exposed to at night has also been linked to rapid aging. The mitochondria in your eyes have to produce a lot more energy than normal to process blue light. When the mitochondria in your eyes are overtaxed, the rest of your mitochondria get stressed, too. This causes metabolic problems and inflammation throughout the body, which of course increases your risk of the Four Killers.
One study found that adults who were exposed to blue light while eating in the evening had higher glucose levels, slower metabolisms, and more insulin resistance compared to adults who ate in dim light.28 Get some candles or at least a dimmer switch, like I have in my dining room. It’s way cheaper than diabetes.
People exposed to high levels of outdoor blue light at night also have a higher risk of developing breast cancer and prostate cancer, compared to those who had less exposure.29 Other studies have found that a disrupted circadian clock increases your risk of cancer.30 Blue light exposure is also linked to obesity and metabolic disorders, which are both significant risk factors for cardiovascular disease.
Blue light can also lead to macular degeneration—damage to the retina that often leads to vision loss.31 More than 11 million people over the age of sixty, including my father, have some form of macular degeneration, so it’s an issue that hits close to home.32 If you’d like to join me on my quest to live beyond a hundred and eighty, you’ll want to be able to see as you age. Cutting out some blue light is not optional, unless you’re okay with becoming one of the 100 million plus cases of macular degeneration I’m forecasting over the next decades.<
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We know that macular degeneration is a mitochondrial disorder and possibly also a blood coagulation disorder. To keep your eyes working, use all the mitochondrial hacks in this book, and make sure your blood is as thin as it should be. Fish oil, or better still, krill and fish roe oil, and turmeric are some anti-inflammatory supplements that can help. I take those and the eye-specific formula I created for Bulletproof and do every one of the items on the following list at least some of the time.
After a recent very detailed eye exam conducted by a leader in the field, I received some fantastic news: “Dave, even though you’re forty-six, your eyes are exhibiting none of the signs of reduced flexibility expected for your age. You’re 20/15 in both eyes, and can read the very finest print on the test. It’s probably because of your glasses [TrueDark half–blue blocking], your diet, and your supplements.” Boom.
Even if blindness doesn’t worry you, you must reduce your blue light exposure in order to reduce your risk of dying. Here’s how:
Unplug or cover unnecessary electrical devices in your bedroom. Go through your room and unplug or tape over LEDs to black out your sleep area. I carry special die-cut dots (or sometimes electrical tape) with me when I stay in hotels so I can tape over the omnipresent blue LEDs on televisions, air conditioners, and alarm clocks.
Invest in blackout curtains. If you try just one sleep hack, make it this one—it’s a serious game changer. A dark room equals better sleep. Even with blackout curtains, watch out for the light that seeps in all around the edges of the curtains. Buy some Velcro and tape down the sides and put a valance on top, or just use foil over your windows. No, it’s not exactly stylish, but it’s a fair trade-off for quality sleep in my book. If you’re working with a window-covering company, use these words: “This job will be a failure if I can see any light at all coming in past the blackout shades.”