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How does sleep affect male fertility? An underexplored aspect of reproductive health

By: Benjamin Bréant, PhD student at the University of Oxford, Pembroke College, in the Department of Physiology, Anatomy and Genetics, on the Interdisciplinary Bioscience course (Doctoral Training Centre), funded by BBSRC (UKRI). He studies the ever-changing patterns of activity in the brain associated with sleep and wakefulness. He graduated from the Faculty of Science of Sorbonne Université, Paris, with a BSc in Life Sciences and a MSc in Integrated Biology and Physiology. Among other things, he is joining us at Jack Fertility to bring more insight into the brain behind fertility.

Why does sleep matter for fertility?

Sleep is at the core of many regulatory behaviours. While it is easy to think of sleep as something good exclusively for the brain and memory, keep in mind that it is beneficial for many other bodily functions and that a healthy brain will also positively impact your body as well. Having a healthy balance between sleep and wake cycles is often associated with better mental health but also better hormonal regulation in rodents and humans which directly impacts male fertility.

Improving your sleep should be one of the go-to ways to improve your fertility. Here, we will detail what is sleep, an easy way to self-monitor your own sleep as we do in labs, but also some advice on ways to improve your sleep.

A short disclaimer before we dive deeper into the subject. Pathologies of sleep exist which can heavily disrupt sleep cycles. If you or your partner report abnormal sleep patterns, heavily disrupted sleep, or any other chronic abnormalities, please reach out to a health specialist. It is important to note that while researching the links between sleep and fertility, very few studies were found. Here, we are not claiming that better sleep will definitely improve and solve the male infertility crisis. Sleep, however, is a needed function for restoring your brain and body functions (similar to eating), and disregarding your sleep will be detrimental to both short and long-term health. On the very same note, research on the benefits of sleep on male fertility is still under-funded, which we will discuss at the end of this piece.

What is sleep?

A male lion sleeping on its side on a green patch of grass.
Sleep is a resting state wiedely spread in the animal kingdom. (Photo: Philippe Clemen / Canva)

Sleep, in broader terms, is a resting state where your body is inactive and disconnected from the environment. As peculiar as it is, sleep is heavily conserved in the animal kingdom. Indeed, from cats to dolphins, lizards, birds, jellyfishes and even fruit-flies, everything and everyone expresses some form of resting state. From cats to dolphins, lizards, birds, jellyfishes and even fruit-flies.

Healthy human adults need on average between 7 and 9 hours of sleep. This amount varies wildly in the population though, as a typical range is between 6 hours and 11 hours of sleep! This changes with age as well, with new-borns needing 14 to 17 hours of sleep and teens between 8 and 10 hours.

Graph representing the average amount of sleep needed decreasing with ages for humans. The text reads: "The estimated range for sleep need in an adult is from 6 hours to 11 hours of sleep per day."
The average amount of sleep needed changes drastically with age.

The drive for sleep is mediated both by the time of the day and your inner clock, as well as the need for sleep increasing the longer you have stayed awake. This means that sleep is not just about sleeping, it is also about regularity: sleeping at the right time (for you that is).

Done well, sleep function has been linked to memory consolidation, but also recovery and maintenance of your immune system, hormonal balance and stress levels. Indeed, hormones directly involved in the regulation of the reproductive system such as testosterone, oestrogen and thyroid hormones, are poorly impacted by an imbalanced sleep. All of that make sleep a good ally when it comes to wellbeing and a necessary component in the maintenance of a healthy male fertility as a disregulation of your inner clock could lead to higher rates of infertility.

Am I a good sleeper?

A man in a t-shirt writing notes on the lined page of a journal.
Monitoring your sleep can easily be done through journaling. (Photo: Anete Lusina / Canva)

First, why would this question matter? As I said earlier, Sleep is a key element in the regulation of many functions in your body. With that in mind, making sure you have the best sleep possible with your way of life and tweaking your way of life towards healthier sleep will without the shadow of a doubt have long-term benefits that will cascade down into improving your fertility.

It is surprisingly easy to self-monitor your sleep. The key is to have a sleep journal. Use what you like best, whether it is a physical journal with pen and paper, or notes on a tablet, or a spreadsheet. It can also help to have an app on your phone or a smartwatch. These last options can only give an estimate of your sleep architecture, when it comes to the rating of your sleep!

First, I would recommend monitoring your day, hour by hour. Note the time when you laid down in bed, and the (estimated) time you fell asleep.

Then, note the time you woke up, and the time you got out of bed. You should then note the quality of your sleep (if you feel rested or not) and the quality of your wake (if you struggled to wake up or definitely needed more time to sleep).

You should also monitor your day-time sleepiness.

Here are the key elements to keep track of:
  • The total amount of time spent in bed – from when you lie down to when you wake up.

  • The time to sleep onset – when you fall asleep.

  • The time you took to get out of bed

These three elements will give you an estimate on whether you indeed struggled to wake up or fall asleep. For example, should you spend more than 20 minutes in bed trying to fall asleep and you have no known sleep pathology, it is recommended to get out of bed and do something else, as the frustration induced by the struggle will prevent you from falling asleep. Monitoring your sleep time is also a good indicator on whether you had enough sleep.

  • The subjective quality of sleep

  • The subjective quality of waking up

These will let you know whether you slept well, and enough. There are many reasons leading to lowering the quality of sleep and waking up, some of which I will detail below. However, the main one is a high sleep debt induced by chronic sleep deprivation.

  • Regularity

That is whether your bed times vary widely. You should aim to have them as regular as possible. Having roughly the same bed times from days to days with the same amount of sleep will help your body to expect that these are the time when it can rest and will increase sleep efficiency. Of course, you need to give yourself enough time.

  • Sleep stability

  • Other comment made by your partner (if you share a bed or the room)

Sleep stability is how many times you woke up during the night, either to go to the bathroom or because something else woke you up.

Should your sleep be disrupted, you should try to limit the cause as much as possible. Talk to your partner, or whoever you might share a room with, as they might notice some of the things your do while your consciousness fades away (snoring, gasping for air, brisk movements). These factors might hint towards a sleep disorder.

An example of how to keep track of these elements can be found below. You can do it manually or with the help of a device of your choice.

Template for a hourly day tracker. Each day is divided into 24 boxes in which one can report whether they were asleep, exercising, eating, or going in and out of bed.
Tracking your day by the hour doesn't have to be precise, as long as you can easily keep track of what happen, you should start to see a pattern appearing.

How to sleep better?

Chances are, you might not be sleeping well! A vast majority of people are not sleeping according to their needs, are experiencing sleep disruption or symptoms of common sleep disorders. All of that put together can be detrimental to your fertility. If you are trying to conceive, you want to maximise your chances of having healthy sperm. Sleeping better is one of the many things you can improve which may also improve your fertility.

Sleep is a recovery process, so if you don’t feel recovered, I have listed here the most common factors which can negatively influence your sleep. If you are experiencing chronic sleep disruptions, insomnia, paralysis or any type of parasomnia, I heavily recommend seeking professional advice. Even though a healthy sleep is key to improving your wellbeing, but there might still be some underlying condition impacting your wellbeing and possibly fertility which should be investigated further by clinicians.

Minimise Caffeine
Two men drinking coffee by their desk in the evening.
Coffee is a commonly used stimulant with poorly advertised adverse effects.

The first culprit of bad sleep is, of course, caffeine. If you are a heavy coffee drinker and have at least one cup of coffee or any caffeinated beverage in the afternoon, it will badly affect your sleep! Depending on the time of the day you take your final cup; you might find it harder to fall asleep - which can be infuriating.

You might think you are actually on the lucky side if you don’t have any trouble falling asleep after your afternoon cup. Well, indeed, an afternoon cup will not prevent you to fall asleep, but will deeply alter your sleep cycles and the expression of your sleep stages by keeping you in the lightest stages of sleep. Long story short, the recovery effects of sleep will be strongly altered.

And then there is caffeine addiction. In his recent book, Michael Pollan describes his experience trying to go for a month without coffee. Caffeine will make you feel awake in the morning, no doubt there. However, it is an addictive compound. The veil the first cup of coffee seems to be lifting in the morning can be linked to a certain need for caffeine that your body has developed. You might not be tired, you might just need caffeine.

So, if you are a caffeine drinker, try to reduce the amount you are drinking and keep your caffeine for the morning as much as possible.

This should help you have a more stable sleep, and should help your body recover from the tiredness accumulated throughout the day, amongst many things. With a more stable sleep, you can expect your overall biological processes to be more effective, including sperm production.

Regular habits

As I said earlier, sleep is driven by a need for sleep, increasing with the amount of time you spend awake, but also the time of day. Your inner clock is telling your body at what time you should fall asleep.

Regularity is key for your body processes regulated by this circadian clock. Everything that you do requires a certain amount of energy. If you are regular in your habits and exercise, eat and go to bed at around the same time every day, then it is hypothesised that your body will dedicate more resources to these actions and will be more efficient.

You can see for yourself what your typical day looks like by keeping an agenda. Note the time you woke up every day, when you ate, when (and if) you exercised. I’d recommend using colours, so you can spot patterns more easily.

At first, if you notice your schedule is all over the place, relax. No need to stress. Do not try to over correct immediately and put yourself into a neat schedule. Change slowly, one thing at a time, and in small steps. If you don’t sleep at regular times, try to pick a time that you know you will be sleepy and use that as a starting point.

To influence your circadian clock and shift your sleep, simply think about jet lag. On forced jet lag during a travel, it will take on average a day per shifted hour. That’s because your circadian clock is heavily using sunlight to set its rhythm. So should you want to shift your sleep, take it slow, and try to reduce as much as possible the light intensity around the time you want to fall asleep.

It is thought that the regularity of sleep will train your body to recover within certain set periods of time. By doing so, you will become more efficient when setting these processes in motion: you should then feel more rested more easily, and your levels of stress should be lowered as well. With stress being a major culprit in the diminution of male fertility, having a better, more efficient sleep will help you keep stress level down as much as possible, which in turn should improve male fertility.

Environmental factors

Sleep can be disrupted by a plethora of other things. Notably the environment you sleep in. It is usually recommended to keep your room temperature quite low when you sleep, and to keep the noise and light disruption at a minimum. If you sleep with your partner, or with a pet, they might introduce some disturbance too! In that case, having a better sleep is not just a you thing, and you might want to talk to them about changing your routine together.

If you are interested in understanding your sleep better and finding ways to improve it, I would recommend reading Matthew Walker’s Why we Sleep, available in physical, digital and audiobook. If you would like to know more about the effect of caffeine, I would then recommend getting a hand on Michael Pollan’s This is your mind on Plants. Both books are accessible to a non-specific audience and are a great step into the world of sleep and altered state.

Fertility and Sleep research

As I said at the beginning of this post, the links between sleep and male fertility is still under explored. The field of sleep research is blossoming at the moment. Indeed, sleep is a heavily disrupted process in our society while at the same time being at the centre of the recovery processes of our bodies. The idea that sleep can be at the centre of many therapeutic approaches to improve mental health and overall wellbeing is promising. Our product has the potential to lead the way towards greater access to male fertility diagnosis, but the quality we promise shows we can be used for research purposes, increasing laboratories' ease of access to data from healthy controls to individuals seeking answers.

Male fertility is decreasing every year and so are the associated research funds. The causes of such a decrease might be diverse, but men are lucky enough that their troubles have a decent chance of being reversible. A healthier way of life comes with increasing chances of having healthier sperm. And with sleep being such a multi-tool of body fixing solutions, it is astonishing that the link between these two has been under-investigated.

Should an unlimited amount of money be diverted into this field, the resulting boom in discoveries will be quite large. Even the basics have been poorly covered and are yet to be explored deeper.

Sleep deprivation experiments are an excellent first step, as they show a direct link between an acute or chronic lack of sleep on brain chemistry and behaviour, and we can easily dose and monitor hormonal levels to see a direct impact on how the body reacts to such a stressful state. These experiments would address how the lack of sufficient quantity of sleep can affect male fertility.

While it is possible to infer how unstable and irregular sleep can be correlated to poor sperm quality, sleep disruption experiments should show a better link between sleep quality, stress levels and fertility. But we would still be missing a direct link between a healthy sleep and healthy sperm. Indeed, so far we have only inferred, as I did throughout this post, that through sleep’s many processes, the body is in a healthier state which can then induce higher sperm quality. Funding opportunities in circadian research exist, but we need more towards interdisciplinary research. Institutes are now sprouting all over the country to offer trans-disciplinary collaborations and they represent our greatest ally towards medical innovation.

We are now facing another knot typical in sleep research: indeed, sleep is important for countless body functions. Establishing a direct link between sleep and fertility requires molecular studies and experimentation at a cellular level. Discovering the molecular pathway regulating fertility that is heavily impacted by sleep would be an excellent research project that could then establish the discovery of new treatments. And we hope Jack Fertility can be a player in this road to discovery.


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