It’s fair to say that Matthew Walker is as close to a sleep guru as it gets. As Professor of Neuroscience and Psychology and Director of the Sleep and Neuroimaging Laboratory at the University of California, Berkeley, he knows a thing or two about nodding off. Here he shares the latest research and wisdom on how workouts and what you eat can impact on the quality and quantity of sleep you get, plus his one essential commandment for catching some z’s...
“For those of us who are not suffering from insomnia or another sleep disorder, there is much we can do to secure a far better night of sleep using what we call good “sleep hygiene” practices, for which a list of twelve key tips can be found at the National Institute of Health website (US).
All twelve suggestions are superb advice, but if you can only adhere to one of these each and every day, make it: going to bed and waking up at the same time of day no matter what. It is perhaps the single most effective way of helping improve your sleep, even though it involves the use of an alarm clock.
That said, two of the most frequent questions I receive from members of the public regarding sleep betterment concern exercise and diet. Sleep and physical exertion have a bidirectional relationship. Many of us know of the deep, sound sleep we often experience after sustained physical activity, such as a daylong hike, an extended bike ride, or even an exhausting day of working in the garden. Scientific studies dating back to the 1970s support some of this subjective wisdom, though perhaps not as strongly as you’d hope. One such early study, published in 1975, shows that progressively increased levels of physical activity in healthy males results in a corresponding progressive increase in the amount of deep NREM sleep (dreamless sleep) they obtain on subsequent nights. In another study, however, active runners were compared with age and gender matched non-runners. While runners had somewhat higher amounts of deep NREM sleep, it was not significantly different to the non-runners.
Larger and more carefully controlled studies offer somewhat more positive news, but with an interesting wrinkle. In younger, healthy adults, exercise frequently increases total sleep time, especially deep NREM sleep. It also deepens the quality of sleep, resulting in more powerful electrical brainwave activity. Similar, if not larger, improvements in sleep time and efficiency are to be found in midlife and older adults, including those who are self-reported poor sleepers or those with clinically diagnosed insomnia.
Sleep may have more of an influence on exercise than exercise has on sleep.
Typically, these studies involve measuring several nights of initial baseline sleep in individuals, after which they are placed on a regimen of exercise across several months. Researchers then examine whether or not there are corresponding improvements in sleep as a consequence. On average, there are. Subjective sleep quality improves, as does total amount of sleep. Moreover, the time it takes participants to fall asleep is usually less, and they report waking up fewer times across the night. In one of the longest manipulation studies to date, older adult insomniacs were sleeping almost one hour more each night, on average, by the end of a four-month period of increased physical activity.
Unexpected, however, was the lack of a tight relationship between exercise and subsequent sleep from one day to the next. That is, subjects did not consistently sleep better at night on the days they exercised compared with the days when they were not required to exercise, as one would expect. Less surprising, perhaps, is the inverse relationship between sleep and next-day exercise (rather than the influence of exercise on subsequent sleep at night). When sleep was poor the night prior, exercise intensity and duration were far worse the following day. When sleep was sound, levels of physical exertion were powerfully maximal the next day. In other words, sleep may have more of an influence on exercise than exercise has on sleep.