Night Moves: Why Delta Sleep Matters

In our tech-saturated, overstretched lives, sleep is the new calorie counting, the new sex, the new god. The latest findings may not stop the worry, but they'll help you obsess about the right things

Photograph by Juan Camilo Palacio Ruiz/ GalleryStock

Photograph by Juan Camilo Palacio Ruiz/ GalleryStock

Among the food porn and humblebrags, a new phenomenon has been stealthily creeping into our Facebook and Twitter feeds: the sleep graph. These zigzagging charts of restlessness and slumber, transmitted from increasingly popular sleep-tracking apps, can stoke much the same envy—she gets eight hours a night?!—as a former co-worker’s luxe holiday. Like food, sleep has transformed from system requirement to status symbol, and we’re obsessed with getting it.

For decades, popular attention in the sleep arena has been focused on a) logging those elusive eight hours a night— the number suggested by the National Sleep Foundation— and b) REM sleep, when eyes move frenetically beneath the eyelids, brain waves spike and the weirdest of weird dreams emerge. But then we started getting hip to the magical, mysterious delta sleep, the slow-wave or deep sleep that repairs injuries and gives us energy for another day. Forget if we were sleeping, the new question is: Are we sleeping efficiently?

“Deep sleep is actually the stuff you want,” confirms Colleen Carney, a psychologist and the director of the sleep and depression lab at Ryerson University in Toronto. She’s also a co-author of the recently released Goodnight Mind (New Harbinger, $20), a self-help manual for treating fatigue and insomnia by creating the optimal conditions for delta sleep—and an ironclad eight hours in bed isn’t one of them. Alas, delta sleep is basically untrackable by smartphone.

So where does that leave the sleep trackers? Every night, about 10,000 Canadians activate the Sleep as Android app and place their smartphones under their pillows. The $2.99 program uses a small sensor already inside our phones, called an accelerometer—it’s what figures out whether you want the screen oriented horizontally or vertically—to analyze when and how much we’re moving, then feeds the information through an algorithm to calculate sleep length and quality. Worldwide, over a million people use the app, reviewing morning-after graphs that claim to show the peaks and valleys in sleep depth, as well as any middle-of-the-night awakenings.

One such devotee is Terri Rowan. Two years ago, the 39-year-old Guelph, Ont.–based massage therapist noticed a friend posting graphs of her sleep patterns on Facebook.
“I was working six days a week and training for a marathon,” she says. “I was trying to make sure I was getting enough sleep.” She first downloaded Sleep Cycle for her iPod, then switched to Sleep as Android.

Rowan credits the app with helping her stick to good sleep habits. She loves the “time to bed” feature: After telling it how much sleep she wants (seven-and-a-quarter hours on a good day) and when she’d like to wake up, it calculates what her ideal bedtime is, then sets an alarm for 45 minutes before that.

“[Then] I know it’s time to start winding down,” she says. “Whenever I’m out late, I hold it up like, ‘Hey, my phone says I have to go to bed in 15 minutes!’ If I don’t ignore it, then yes, I do feel more rested.” Friends don’t tease her about tracking, she says—either they dismiss it as “a lot of work,” or they end up buying the app themselves.

Sacha Chua, a Toronto IT consultant, has tracked her sleep for years. She’s one of the organizers of Quantified Self Toronto, a 400-member organization of personal data crunchers who get together to discuss the latest tools and findings—weight tracking is probably the most popular topic of conversation, says Chua, followed closely by exercise, then sleep. The 30-year-old regularly analyzes her data to understand how she spends her time, ensuring she’s not too overcommitted to get sufficient sleep. “The average Canadian gets slightly under eight hours and I average 8.5,” says Chua, a charmingly sincere nerdy type who refers to the global time studies done by the Organisation of Economic Co-operation and Development to compare herself to everyone else on the planet. She says that after a few weeks or months of analyzing sleep data and daily schedules, most of us are more mindful of where we’re spending our time. “It turns out we’re really good at lying to ourselves,” she says.

“Tracking lets you make better decisions.”

But while Rowan and Chua swear by their trackers—as do, anecdotally, many of my friends and acquaintances—sleep doctors remain unconvinced.

“The average Canadian gets slightly under eight hours, and I average 8.5″—Sacha Chua, devoted sleep tracker

“I tell patients to avoid clock watching,” says Dr. Elliott Lee, a sleep specialist at the Royal Ottawa Mental Health Centre. “The more they think about sleep, the worse it is.” Plus, there’s the very big question of how well phone-based trackers work. “An accelerometer in the bottom of a pillow—I don’t understand how reliable it would be to pick up REM versus delta sleep,” he says.

A quick refresher: Sleep happens in five stages—1 and 2 are the transition into sleep, 3 and 4 progress deeper into delta, and the last is the much lighter REM, when brainwaves look the same as during waking hours. For an average adult, a good night’s sleep would be cycling through the stages four or five times, without waking up for more than 20 minutes.

Quality snoozing, says Carney, relies on a delicate interplay among various systems and chemicals in our body. Most important for delta sleep is the sleep homeostat, which assesses the length and depth of your last period of rest (whether during the night or an afternoon nap), helping to make you sleepy at what is hopefully the appropriate time. “From the moment we get up to the moment we go to bed, we’re building up a chemical called adenosine, which pressures the system to go to sleep,” she explains. Ideally, enough adenosine has built up by bedtime that the chemical outmuscles scheduling, anxiety or stress, kicking off a deep slumber marked by the lazy, slowly oscillating brainwaves of delta sleep. (Caffeine can directly inhibit the production of adenosine, as can certain asthma medications.) Most of our deep sleep happens in the first half of the night. Once adenosine is burned off, the homeostat gives way to the circadian system, an age-old biological clock in every cell that responds to time-sensitive cues such as light, hunger and regular activities like exercise or work.

Those big chunks of delta sleep in the first half of the night are when we produce the majority of human growth hormone, the chemical responsible for everything from bone density and muscle mass to injury recovery and immune function. “If you don’t have deep sleep, you’re more likely to have little aches and pains—we know that people who have fibromyalgia don’t get as much,” says Carney. A lack of deep sleep and growth hormone production has also been linked to insulin sensitivity and the development of diabetes.

Like Lee, Carney is skeptical about the effectiveness of commercial sleep trackers. Aside from the issue of whether or not trackers can accurately measure delta sleep, many fans of phone-based apps swear by a common alarm feature that promises to wake users during a light sleep phase, such as 1, 2 or REM. But both doctors say that the vast majority of deep sleep happens in the first part of the night, so the chance of being woken out of a restful state in the early morning is low. As well, sleep labs like the ones at Ryerson and the Royal Ottawa attach patients to electroencephalograph (EEG) machines, which measure minute changes in the microvoltage of brain waves in order to monitor sleep length and quality. Commercial trackers, on the other hand, use less accurate algorithms—in combination with the phone-based motion sensor—to determine whether a user is in heavy, unmoving slow-wave sleep, in twitchy stage 1, stage 2 or REM sleep, or fully awake.

“Any formal measuring would be extremely difficult,” says Martin Stava, Sleep as Android’s co-founder and developer. “One of the key factors is actually the phone you have; there are huge differences between devices even from the same manufacturer. We try to design our algorithms to be resilient to these variations, but some phones will likely work better than others.” Stava also points out that the bed itself is a factor—a soft mattress might transmit more movement than a firm one.

Stava discloses that his app has been formally tested only by a small sample: himself, his co-founder and their wives—but some sleep trackers may not be tested on any women at all. Women’s sleep patterns and depth of sleep change throughout our menstrual cycles, as well as during pregnancy and menopause, notes Lee. For these reasons, our sleep cycles are often seen as too complicated for simple studies, so male data is assumed to be adequate. It’s not. Take obstructive sleep apnea, a condition that prevents deep sleep and is most often caused by a collapsed or blocked airway. It leads to many short awakenings throughout the night—though these periods of unrest might be imperceptible, sufferers have greater difficulty reaching and maintaining deep sleep. Because the majority of obstructive sleep apnea studies have been conducted on men, its best-known symptoms are snoring and daytime exhaustion. Both Sleep as Android and Sleep Cycle (whose creator did not respond to my interview request) promise to record bouts of snoring for next-day analysis, one feature that helped a male acquaintance of mine realize he had an issue and get treatment for sleep apnea. “With women it’s more subtle because they usually don’t completely stop breathing,” says Lee. “They might feel fatigued, or a little depressed. They tend not to snore because they have lower upper body strength.” And because a female sufferer of sleep apnea will probably snore less than a man with the same problem, her smartphone could tell her that her sleep quality is good, or even excellent, but all that feedback really indicates is that she’s not a boorish, sawing beast.

While the old ideal of eight hours a night may no longer hold true, Carney admits this new thinking can be a tough sell. “I’ll say [to a client] … what if you could still get six hours of sleep, but you could feel really good? If they say, I’d still want more sleep, then I know we have some work to do.”

This doesn’t mean sleep isn’t crucial to health. Carney points out that most of the scary stories about what a dearth of it can do to your health— diabetes! heart disease! obesity!—are accurate, but not for natural insomniacs. Rather, it’s people who choose to restrict their sleep who typically suffer—especially if they’re doing so to spend more time at work or on the couch, since a sedentary lifestyle also interferes with delta. At the same time, while front-end delta is indeed the most restful sleep stage, it doesn’t mean you can cut short on the back end without consequence. “Look at sleep like a symphony; removing any part distorts the function,” says Lee.

So, what’s your best bet for increasing delta sleep? No caffeine after noon, to allow for adequate adenosine buildup before bedtime. Lots of exercise: cardio in the morning, yoga as the day winds down. Absolutely no screens in the bedroom, since the backlighting convinces your eyes and brain that it’s daytime, sending alertness signals to your circadian system. Regular bed and wake times, no sleeping in on the weekends and no naps over 30 minutes, since daytime sleep robs us of exponential minutes of nighttime delta. The human body revels in routine and will soon settle into a regular pattern, at which point you’ll truly know how much you need.

The new thinking on sleep makes it increasingly comparable to sex: Sometimes a quickie feels great; other times, it’s a marathon session. As opposed to fixating on quantity, it’s a dedication to quality that’s key to long-term satisfaction. Of course, also like sex, only a lucky few get that for a lifetime.