Unless you are a sleep expert, you probably haven’t heard much about homeostatic pressure (sometimes referred to as sleep pressure). However, it is one of the main three underlying mechanisms that are essential to understand if you want to have consistently good sleep.
Homeostasis is a principle that explains how our body tries to maintain balance and equilibrium within all of our systems so that we can live a long and healthy life.
Homeostasis is both fascinating and annoying. Fascinating because it means that as humans, we are surprisingly resilient to the bad things that happen in our lives. Annoying because we get used to the good things in our lives rather quickly too. The excellent book by Dan Gilbert called ‘Stumbling on Happiness’ explains this well, as does his viral TED talk video ‘The Surprising Science of Happiness’.
Examples of Homeostasis in Action
TEMPERATURE REGULATION: Suppose we move somewhere that is hotter or colder than our natural environment. Our body will eventually adapt or acclimatise to this. In 2009, I spent four months working in London and saw people sunbathing in Hyde Park with very few clothes on during a 17 degree Celsius day. Then in August 2018, I moved to Vanuatu and saw people wearing jackets and beanies when it was 22 degrees Celsius in the evening. I never thought that I would have to wear a jumper in Vanuatu because of how much I was sweating initially, but sure enough, eight months later in Port Vila I was also reaching for extra layers to stay warm at night.
PAIN SENSITIVITY: Now let us imagine that you have a chronically painful back. If you have never taken any pain medication before, one Paracetamol or Ibuprofen tablet may be enough initially. However, very quickly, you may need two pills a day, and then four, then six, until it is no longer alleviating your pain or you are taking such high amounts that it becomes dangerous for the health of your internal organs. You switch to a stronger analgesic, maybe something with codeine in it, until you get used to that, and then turn to an opiate medication such as Tramadol or even Morphine. Eventually, either you are taking potentially life-threatening doses, or you are in excruciating pain. Through the process of homeostasis, you adapt and develop a tolerance to whatever you consume until it no longer has the desired effect that you want. Your brain is happy because it was trying to send you the pain signals for a reason, but you and your pain doctors are probably not.
PHYSICAL FITNESS: Exercise is the same. If we want to get fitter over time, we cannot just keep doing the same exercise routine week after week. We need to keep increasing the frequency, variation and intensity of our workouts over time so that our body does not fully adapt and continues to increase our strength and aerobic capacity. Our body’s drive for homeostasis means that eventually the same workout will require much less effort, burn fewer calories and fail to improve our overall ability. We must change things up and challenge ourselves more and more.
METABOLISM: To lose weight, we cannot just reduce our caloric intake. Restrictive diets like these may lead to weight loss initially, but eventually, through the process of homeostasis, our metabolism slows, and the weight loss stops. If we then go back to eating what we used to, our weight climbs back up, usually to more than what it was before the diet initially began. Then homeostasis kicks in and increases our metabolism again, and our weight remains relatively stable unless we start eating a lot more or less. Things like intermittent fasting or the 5:2 diet have become the latest fads in weight loss because the variability makes it possible to lose weight over time without your body’s drive for homeostasis wrecking it or slowing down your metabolism. It gives your digestive system a much-needed rest at times too.
Homeostasis in Sleep
Our sleep system is similar to our temperature regulation, pain sensitivity, physical fitness and metabolism in that our brain and body’s drive to maintain homeostasis helps to regulate it. Homeostatic sleep pressure works to help us remain alert enough during the day to function and survive, and tired enough at night to sleep well, help process what we learnt that day, and restore our other bodily systems too. Just as it is possible to be too hot or too cold sometimes, or to eat too little or too much, it is also possible to spend either too little or too much time in bed.
Homeostatic pressure for sleep rises from when we get up in the morning to when we go to bed at night. The longer that we are awake for, the less quickly this pressure rises, but it does make it harder and harder for us to remain awake over time unless we get some sleep. When we nap during the day or fall asleep at night, our homeostatic pressure for sleep declines, with deep sleep (Stage 3 non-REM sleep) reducing the pressure faster than light sleep (stage 1 and 2 non-REM sleep and REM [rapid eye movement] sleep).
If we spend too little time in bed, say under 6 hours regularly, we will not obtain enough sleep to erase our homeostatic pressure for sleep. As a result, our homeostatic drive for sleep increases over subsequent days to try to help us spend more time in bed so that we sleep longer. If we do not spend longer in bed, our brain instead works to help us sleep deeper and better, so that our pressure can drop more quickly each night. As a result, people who spend less time in bed are more likely to fall asleep quickly, have a good quality of sleep, and remain asleep during the night.
Sleep needs vary, but people who only spend 6 hours in bed each night will probably still feel both tired and sleepy during the day because their homeostatic pressure is likely to remain high. By spending more time in bed, say 8 hours regularly, they could still have good sleep quality and not feel as tired or sleepy during the day, because their sleep pressure is minimal in the morning and high enough at night.
It is hard to obtain enough good quality sleep if we spend too long in bed, say over 10 hours regularly. Most people with chronic insomnia do not realise this and spend longer in bed to try to get more sleep. However, all this does is reduce their homeostatic drive for sleep, resulting in a lighter and more fragmented sleep.
If you are already in bed for more time than you need to sleep, your homeostatic pressure is unlikely to be high enough, and your brain will not help you to sleep as much as you would like. By spending less time in bed, or looking at other ways to increase your homeostatic drive for sleep, you can ensure that it is high enough when you go to bed each night.
How can we ensure homeostatic pressure for sleep is low when you get out of bed in the morning and high when you go to bed at night?
If you want to increase your homeostatic pressure for sleep so that you sleep better at night:
- Aim to be up for at least 16 hours each day. You should maintain a regular wake time, even on weekends, and spend a maximum of 8 hours in bed each night.
- If you want to increase your sleep pressure even faster, increase your time awake each day even more (17 hours) and reduce your maximum time in bed further (7 hours).
- The more extreme you make it, the faster your sleep pressure will rise, but try not to reduce your time in bed too far below your actual sleep need.
- To figure out your sleep need, determine your average amount of sleep that you obtained over the past week. Then add 30 minutes to this for your initial maximum time in bed prescription.
- If you have been sleeping approximately 6 hours a night for the past week, setting your maximum time in bed initially to 6 hours and 30 minutes is good.
- If you have been sleeping under 5 hours per night over the past week, do not set your initial time in bed prescription any lower than 5 hours and 30 minutes per night, as this is likely to be unhealthy and unsustainable.
- If you are not sure what your sleep need is, start with 8 hours in bed as your maximum, and aim to be up for at least 16 hours each day.
- For every hour that you are up past your usual bedtime, you can sleep in beyond your ordinary wake time by 30 minutes the next morning. It will ensure that your homeostatic pressure is still high enough the next night when you go to bed.
- If your regular to bedtime is 11:00 pm and rise time is 7:00 am, but you are out of bed until 1:00 am, do not panic. Just sleep from 1:00 am to 8:00 am.
- If you are out until 2:00 am, make sure that you are up by 8:30 am. Out until 3:00 am, sleep until 9:00 am. Out until 4:00 am, sleep until 9:30 am. Out until 5:00 am, sleep until 10:00 am, etc.
- The later you are out of bed past your usual bedtime, the more tired you will feel the next day. You will feel tired because you have slept less and not at your ordinary time, but following this rule will help you to get back on track with your sleep more easily the next night.
- Do not nap during the day.
- Napping reduces our homeostatic pressure for sleep, making it harder to get to sleep at your usual bedtime that night.
- If you have to nap, keep it to under 30 minutes and before 4 pm, and set the alarm if you choose to have a nap so that you do not sleep more than 30 minutes.
- If you do nap for longer than 30 minutes, go to that amount of time later than you usually do to ensure your pressure is still high.
- If you nap for 1 hour, go to bed at 11 pm instead of 10 pm. If you nap for 90 minutes, go to bed at 11:30 pm instead of 10 pm. If you nap for 2 hours, go to bed at midnight instead of 10 pm, etc.
- Consume as little caffeine as possible.
- Caffeine targets adenosine receptors, which reduces our homeostatic pressure for sleep.
- If you have to have caffeine, make it weak, drink tea instead of coffee, or have it early in the day.
- Caffeine has a half-life of approximately 4.5 hours, so 100mg (a regular cup of coffee) 9 hours before bed means that you will still have 25mg in your system when you go to bed that night. It will reduce your sleep pressure a little, or increase your arousal levels, which can also negatively affect sleep.
- Engage in regular physical exercise and challenge yourself cognitively during the day.
- The more we do physically and cognitively demanding tasks, such as exercise or practising new skills, the higher our need for sleep will be that night.
- Because exercise and learning new skills places a certain amount of stress on our body and brain, do not do heaps more than usual. It is better to gradually build up over time and slowly do more and more than we have previously done.
- It is also crucial that we do not engage in rigorous exercise or hugely demanding tasks too close to our usual bedtime. Aim to finish anything too cognitively or physically demanding at least 3 hours before your bedtime, or go to bed a bit later than usual if you have to do these things later than you would like to. Having effective strategies to wind down and relax quickly can also assist if you need to do these tasks shortly before your usual bedtime.
If you want to reduce your homeostatic pressure for sleep in the morning or during the day so that you feel more alert or energetic during the day:
- Sleep longer.
- A good rule to remember is that 1 hour of sleep reduces approximately 2 hours of homeostatic pressure. If we sleep longer, our sleep pressure will be lower, and we are likely to feel more alert and more capable of functioning. I recommended this only if you are currently not spending enough time in bed to meet your sleep needs.
- Be aware of sleep inertia, though. It is normal to feel a bit tired or drowsy when you first wake up, especially if you have been in a deep sleep. It can take anywhere between 1-3 hours before someone feels fully alert in the morning, so if you have already reached your maximum allotment of sleep for that night, try to get up and see how you feel a bit later, rather than hitting the snooze button or turning off your alarm and going back to sleep.
- The more you sleep in beyond your usual time, unless you went to bed later the night before, the later you will need to go to bed that night to ensure that your sleep pressure is high enough for a good night’s sleep.
- Have a power nap.
- If you are feeling sleepy and not functioning well, have a short 15-20 minute nap.
- It could increase your alertness and productivity for the rest of the day and is unlikely to cause sleep inertia when you wake up because you have only had a light sleep.
- It is also unlikely to lower your sleep pressure to the point where you will not be able to get to sleep that night.
- Have caffeine at the right time for you.
- Our body naturally produces cortisol at higher levels in the morning shortly after we wake up to help us become more alert and get going for the day. Caffeine also boosts our cortisol levels. Often known as the stress hormone, cortisol helps if our stress levels are too low and we feel apathetic, unmotivated and unproductive.
- If our cortisol is already high, adding caffeine at this time can make us overstimulated, anxious or irritable in the short-term, or reduce the natural levels of cortisol that our brain releases in the long-term (because of our brain’s drive towards homeostasis), making us more reliant on caffeine to be productive.
- Rather than having caffeine at the same time every day, have it only when you are feeling sleepy, as it can reduce homeostatic sleep pressure by acting on adenosine receptors in the brain. The times when you may most need it are around 9-10 am to help you make it through to lunch, or about 2-3 pm, to help you make it through the post-lunch dip and up until the end of the workday, assuming you work a regular 9 am- 5 pm job.
- Shift workers and night shift workers also need to realise what times it is best to take caffeine so that they can function during their shift and get home safely without it negatively disrupting their sleep.
- Other substances could assist with alertness and energy during the day, such as Guarana, Ginseng, Gingko Biloba, Taurine, B vitamins, especially vitamin B12 if you do not regularly eat meat. So could prescription medications such as amphetamine-based medications (Ritalin), Modafinil or Armodafinil.
- I do not recommend or prescribe any of these substances and do not know how they act on our homeostatic drive for sleep. For more advice, please see a medical doctor.
- Modafinil and Armodafinil do seem to reduce people’s need for sleep based on self-reporting that I have heard, but the Pharmaceutical Benefits Scheme in Australia only endorses these prescription medications for the treatment of Narcolepsy. In the USA, you can also get these medications if you have excessive daytime sleepiness associated with OSA or shift work.
- If you think you may have excessive daytime sleepiness due to OSA or another Primary Sleep Disorder or may suffer from RLS, Idiopathic Hypersomnia or Narcolepsy, please seek a referral to a Sleep Physician from your General Practitioner for a full assessment. The Sleep Physician can then determine if these medications could be useful for alleviating your daytime difficulties without negatively affecting your sleep at night.
Although it may be difficult to sleep well with all that is going on around the world at the moment, good sleep is still possible. This article goes into one of the three main things that you need to know to sleep well on a regular basis. Managing your stress or arousal levels effectively is another aspect that you really need to learn how to manage if you want to sleep well consistently. I will introduce the third element to you soon. Stay tuned.