Quality sleep is an integral part of leading a healthy lifestyle. But what is ‘enough’ sleep and what can we do to facilitate a good night’s rest? We ask the experts for their advice
Whether embarking on a new exercise regime or just trying to be healthier, sleep is the one element that gets overlooked. We might even associate a health kick with less sleep to plug in extra exercise before work. We venerate individuals who “only need” four or five hours sleep a night as we conflate sleeping with laziness instead of acknowledging sleep’s powerful physiological (and psychological) benefits.
We all need to hit the snooze button. Sleep is essential for resetting hormones and it is a core component of our regulatory systems. It affects appetite, our metabolism and even the composition of our body.
Very poor sleep — defined as fewer than four hours over six nights — can result in our brain’s food reward centres being more active, making us more likely to reach for the pastries and treats. In some studies, insufficient sleep has been shown to impair the insulin response, meaning more glucose-free to be stored as fat. Perhaps since it requires no resource and, for most of us, little effort, we tend to think of a good night’s sleep as a reward or a treat.
Admittedly, some advice on the matter can seem sponsored by silk pillowcases and scented candles rather than research and rigour. Cynics might well raise an eyebrow. So here is the science behind why you should get a good night’s sleep,and how. No silk pillowcases are required. A good night’s sleep will help you eat better, which you help sleep better.
We all recognise the feeling of trying to compensate for tiredness with food. Then, because we’ve overeaten during the day, we sleep poorly again the following night. “Nutrition and sleep often operate in a two-way interaction whereby both sleep can impact on subsequent nutrition, and nutrition can have an impact on subsequent sleep,” says Mark Germaine of the school of health and human performance at DCU.
Poor sleep impacts hormone regulation and can specifically depress leptin — the full hormone — and elevate ghrelin — the hungry hormone.
“Some research has shown that when people get as little as five hours of sleep per night, less than the recommended seven to nine hours sleep, we get an increase in ghrelin. Ghrelin is a hormone that is secreted to create the sensation of hunger,” adds Germaine.
“We typically see a decrease in the hormone leptin, which stimulates satiety and has an effect on our metabolic rate which increases the number of calories we burn.” We’re not going to be satisfied with apples, either. “Desire for foods classified as highly processed is often increased to a greater degree than other foods,” says Germaine.
Keeping consistent sleep and wake times is not just a cliche. Our waking hours encourage the storage of a molecule, adenosine, which leads to sleepiness. We use these stores when we sleep.
“Adenosine is believed to increase sleep pressure or sleep drive,” explains Motty Varghese, sleep Physiologist and behavioural sleep therapist at sleeptherapy.ie. “It is a byproduct of the breakdown of the energy currency, which is ATP, adenosine triphosphate, and is accumulated in the brain as one stays awake. It is a hypnogenic or sleep-promoting molecule and this is achieved by reducing the activity of wake-promoting neurons in the basal forebrain.
“Adenosine accumulates in the brain and gets picked up by the adenosine receptors. The more adenosine, the more our alertness is dulled.” Having a consistent bed and wake time will help ensure an adequate store of adenosine to help us nod off.
Tea and coffee do keep us awake — caffeine targets the same receptors as adenosine. Varghese explains: “We feel sleepiness when adenosine binds with certain receptors in the brain. But caffeine can impede the effect of adenosine since caffeine targets the same receptors as adenosine does.” So caffeine blocks the molecules that help make us sleepy, but that’s not all.
“It can take several hours for caffeine to be metabolised and hence the alertness following caffeine ingestion,” Varghese adds.
There is a good way to nap and we could learn a lot from the Spanish. This is because we have two windows when we are naturally sleepy. A nap can reduce our adenosine reserves, so we should leave enough time between napping and sleeping to adequately replenish.
“We have two periods of extreme sleepiness in 24 hours,” explains Varghese. “The first is the primary window of circadian low, roughly between 2am and 5am. If we don’t manage to sleep during that time, we will feel tired the next day. There is also a secondary window — you could call it an afternoon slump — between 2pm and 4pm.”
This doesn’t mean that we should hit the couch for the afternoon. “Ideally we wouldn’t have to nap, but if you have the opportunity and the circumstances, then keep the nap short. Between 15 and 20 minutes is ideal, but never over 45 minutes because this will lead to grogginess.”
Continued exposure to bright light in the evening sends a signal to the brain that it isn’t yet time to sleep. “Sleep is the result of a two-process model,” Varghese says.
“S-model is the accumulation of adenosine during the wake period resulting in increased sleepiness. C-model is about the master body clock. This determines wakefulness during daytime and increased sleepiness at night time. So, the body clock has an internally generated inherent rhythm to keep us alert during the day and sleepy at night. Light acts as an indicator for the body to learn the time in the natural world.”
“Our circadian rhythms are disrupted by exposure to blue light, which is produced by screen devices and also the energy-efficient LED lightbulbs we use at home,” Varghese says.
“The old-fashioned bulbs are friendlier than the new gen because there is more blue light emitted by the LED.” That doesn’t mean we should change our lightbulbs, however.
“Blue light is not all bad,” says Varghese. “It’s extremely useful for us during this time to improve alertness and energy levels, which we know help with productivity.” Getting rid of blue light and dimming all the lights is essential to help the body produce melatonin.
Varghese adds: “Once it is evening, we should dim our house lights, put away the devices so that the body can produce the sleep hormone. We have a point, the DMLO, dim light melatonin onset, that’s two hours before we fall asleep. If someone falls asleep naturally at 11pm, their DMLO is around 9pm.
“When we reduce the light exposure, the body clock will recognise that and it will stimulate melatonin production. And then we are physically ready for sleep.”
“We should assess how we are feeling during the daytime,” advises Varghese. “A lot of individuals have a tendency to look at their FitBit device and say, ‘I only got 10pc deep sleep, I was in light sleep for the rest of the time’. But we shouldn’t judge our sleep entirely by our devices. It’s important for us to assess our own alertness levels and energy levels.
“If you think that’s not optimal, then we should look at the quantity and the quality of sleep. Are you taking a long time to fall asleep or a long time to return to sleep when you wake up at night? Are you waking up too many times at night to spend in the refreshing stages of sleep?”
Alertness is the enemy of sleep. “Identify the source of the alertness — is it anxiety, stress or is it perfectionist tendencies?” Varghese asks. He says we need to be calm and relaxed rather than ruminating obsessively if we want to sleep well. Put down the phone and pick up a book to help you relax.