Sleep is increasingly recognised as far more important than scientists previously thought. I have heard sleep called ‘the tide that raises all health ships’ and that is with good reason. It positively influences your mood, ability to perform complex tasks, allows your muscles to grow, repairs tissues. It even helps fight infection – in one study I read about, researchers demonstrated that good sleep can significantly reduce the recovery time from viral infections – which may be one reason why we often feel tired if we have an infection – it’s the body’s way of getting us to sleep.
But how long should we sleep for?
There’s actually a lot of science around sleep, and various researchers have tried to link the risk of heart disease and strokes to sleep quantity, with some suggesting that less than 6 or more than 8 increases those risks.
My own view on it is that it is much more complex than this. For example, sleep quantity and quality are different beasts. Being unconscious or sedated is different in its biological property to sleep. This is one reason why if you’ve had too much alcohol, you may well fall ‘asleep’ easily, but wake feeling un-refreshed. You are more likely sedated than properly asleep, and missing out on the benefits.
US health authorities recommend that adults ages 18 to 60 years should get at least 7 hours of sleep each night, but only 65.2% of adults surveyed in United States in 2014 reported that they consistently meet this standard. Inadequate sleep has been associated with a range of adverse health effects including diabetes, high blood pressure, mental distress, and an increased risk for accidents.
There is also mounting evidence supporting the notion that sleep duration may have an effect on cardiovascular health, with several studies linking both insufficient AND excessive sleep duration to an increased risk for cardiovascular disease.
A review of 74 studies indicated that self-reported sleep duration exceeding 8 hours per night—but not sleep duration <7 hours—was associated with an increased risk for all-cause mortality and cardiovascular events.An association was also observed between subjective poor sleep quality and an increased risk for coronary heart disease.
A couple of other studies have found that after adjusting for age, sex, physical activity levels, depression, and other potentially confounding variables, short sleep duration (ie, <7 hours per night) was found to be associated with a greater prevalence of previous heart failure, stroke, diabetes mellitus, heart attack and high cholesterol. In addition, longer sleep duration (ie, >9 hours per night) was found to be associated with a greater prevalence of previous stroke, coronary artery disease and heart failure.
More research is needed, but one wonders if the increased cardiovascular risks associated with short and long sleep durations may be attributed to factors such as metabolic impairment and lifestyle behaviours including poor dietary and exercise patterns. Sleep apnoea (stopping breathing at night) may be associated with longer sleep duration and has been linked to greater cardiovascular risk across various studies.
As you can see, there are some variations in the literature, but for most people a take home message of aiming for 8 hours sleep per night would seem reasonable. That’s certainly what I aim for, and always feel better for it.
I have had quite a few questions from members about this article on sleep, so thought I would answer them below. Many questions related to whether it mattered if sleep length varied. My first comment then is that the sleep duration quoted in trials and so on are averages. We will all have spells where we sleep less well, and that is fine. It is the average over a long period that is more important. When we are under stress we sleep less well: if we have work deadlines or family worries for example. This is normal and will affect us all at one time or another. There will also be outliers. Margaret Thatcher famously survived on only 4 hours sleep per night. I guess whether that was good or bad is a matter of opinion!
What about naps?
Well, the science tells us that naps are neither good or bad for you, but are highly individual. Some people will do well to nap, others not. However, if napping, be sure not to go on too long. The reason we sleep from a biological perspective is that levels of the neuro-transmitter (a chemical which circulates in our nerves and communicates with our brains) acetylcholine build up during the day to the point that they signal it is time to sleep. If we nap, the levels of acetylcholine reduce (think of a tap being opened), such that they will be lower than they should be later in the day and not signal to us appropriately when to sleep. I personally almost never nap, and if I do, I take it as a sure sign that I need to address exhaustion, and ensure I get enough quality sleep over the next few days.
What happens when we sleep?
The first part of sleep is called non-REM (rapid eye movement) sleep, and has 3 stages. The first two are light, and typically last up to 25 minutes. Beyond this, you go into a deep sleep stage, and if woken will likely feel groggy and disorientated (another reason not to have a long nap). REM sleep follows, typically for about 90 minutes, during which you are paralysed. Yes you read that correctly. It makes sense though, as this is when we dream. Imagine the trouble you could get into if your body was able to move when it thought it was being chased by a lion in a dream…
The whole process then repeats itself. I occasionally use the sleep tracker on my watch to get an idea of how long I spend in the different sleep stages. However, if I’m honest I’m not sure how accurate my particular app is, and even so, I’m not sure I can alter them, and don’t want to worry myself if I’m not getting ‘perfect sleep metrics’ when I review them the next day. I think it’s best if I simply adhere to good sleep hygiene (see below).
What about interruptions?
How detrimental are sleep interruptions? Well, it depends what those interruptions are. There is good data to show that chronic night shift workers are at increased risk of heart attacks and strokes, but bathroom breaks in the middle of the night which are sadly common for many of us do not cause a problem on the whole as you can get off again easily afterwards. This sounds silly and simple, but altering the time you last consume fluid before bed can make a huge difference to night-time bathroom breaks!
Sleep supplements
There are a number available, but by and large there is little scientific data to support their use. In part this is because of the difficulty performing quality human studies using supplements (compared to prescription drugs). They are not regulated in the same way, and there is also an issue regarding being sure what is actually in them, particularly when purchased online. Many sleep inducers are sedatives, and in some cases this has the potential to be addictive, with other side effects such as day-time drowsiness. Often supplements are plant-based derivatives, but the amount of active ingredient can vary, as can an individual’s tolerance to the compound.
Melatonin is one of the best known sleep supplements, and has been extensively studied. Many jet-lag remedies include this as an active ingredient and are popular worldwide. However, melatonin levels can be optimised without taking a supplement: adequate darkness at night, reduced artificial or blue light at night, adequate dietary protein and anti-oxidant consumption, a diet rich in lutein (eg kale, spinach, broccoli, corn…) will all increase natural levels of melatonin and should definitely be optimised before thinking about supplementation.
Other compounds which have been studies include Magnesium L-Threonate, L-Theanine, Apigenin and Myo-Inositol. L-theanine is found in green tea, and helps reduce anxiety as part of the reason for its use as a sleep aid. Apigenin is a polyphenol found in chamomile, and has reported benefits in sleep as well as other conditions such as diabetes and Alzheimer’s. Myo-Inositol has been shown beneficial in sleep quality in pregnant women. My advice would always be to seek individual advice from your healthcare professional in the first instance.
What about sex?
Often a sensitive topic, but one that we should not shy away from discussing. Interestingly this has indeed been shown to increase levels of sleep hormones within the body. Sex promotes sleep, but also sleep promotes sex: one study showed an additional hour of sleep increased women’s appetite for sex by 14%.
The more I’ve read and learned about sleep, the more convinced I am that it forms a key pillar of health, and something that we should be going out of our way to improve. I’ve started asking about my patient’s sleep more in my consultations, and it’s often amazing where that conversation takes us. It can be highly relevant to their cardiac symptoms!
This long blog (and believe me, I could have gone on longer!!) I think only serves to highlight how important sleep is for us, and all aspects of our health. Pay attention to it, and I guarantee you will feel better for it.