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Sleep and female fertility

Robbie Puddick
Written by

Robbie Puddick

Medically reviewed by

Fiona Moncrieff

10 min read
Last updated July 2024

Jump to: Three ways sleep harms female fertility | Three tips to improve your sleep | Have a consistent sleep routine | Avoid technology before bedtime | Be mindful of your caffeine intake | Take home message

Sleep is a critical part of a healthy lifestyle, and it’s also essential in regulating the menstrual cycle and improving female fertility. A woman’s body is constantly preparing for pregnancy, and a lack of sleep can disrupt this delicate process.

Research suggests that poor sleep quality and sleep duration (particularly under 5 hours a night) can affect ovarian function, menstruation, and IVF outcomes. One study found that sleep duration predicted 40% of the variability of anti-Mullerian hormone levels (a marker of ovarian follicle count) and the number of oocytes (eggs) retrieved during IVF.

Lack of sleep can harm female fertility in three crucial ways:

  1. Worsens insulin resistance: Insulin resistance leads to excess production of androgens like testosterone, disrupting the hormonal balance of key sex hormones such as SHGB.
  2. Increases cortisol levels: High cortisol levels directly inhibit the hypothalamus and pituitary gland, suppressing the release of crucial sex hormones FSH and LH. It can also lead to excess testosterone production and worsen insulin resistance.
  3. Disrupts the balance of hormones needed for ovulation and fertility: Outside of insulin resistance and cortisol, inadequate sleep seems to directly disrupt the production and secretion of crucial sex hormones and increase chronic inflammation, which can directly harm ovarian function.

Fortunately, there are practical ways to improve your sleep over the long term that will improve fertility and increase your chances of a successful pregnancy and healthy live birth.

Here are our three tips to improve your sleep:

  1. Have a consistent sleep routine.
  2. Avoid technology half an hour to an hour before bedtime.
  3. Be mindful of your caffeine intake.

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1) Have a consistent sleep routine

Your body’s cells are all aligned to an internal 24-hour clock known as the circadian rhythm. This has been developed across our evolution and was designed to ensure survival.

For example, cortisol levels rise in the morning to boost alertness with the rising sun; this would have enabled our ancestors to go out to hunt, forage, and be alert for predators. Melatonin then rises in the evening to help us feel drowsy and drift off to sleep to rest and recover for the next day of survival.

This routine has been cemented in our body’s cells. They function at their optimum level when we are more in tune with our circadian rhythms and the rise and fall of the sun. This is why a regular bedtime routine can support our ability to sleep better.

But by going to bed at the same time each night, our body will settle into a regular sleep-wake rhythm, reducing the time it takes us to fall asleep and improving the overall quality of sleep.

Research on maternal mothers supports this. A recent study randomised 123 mothers with 3-18-month-old children to a specific bedtime or no routine (control). The results showed that the mothers reported higher quality sleep, fewer awakenings during the night, and improved mood.

Here are three tips to ensure a regular bedtime routine:

  1. Set a regular bedtime and stick to it: Many smartphones will have a sleep function set up with a reminder to head to bed. Halfway through a film? Pause and return to it the next night – it’s not going anywhere.
  2. Set a regular alarm for the morning: As much as it’s essential to go to bed at the same time each night, it’s also important to stick to your morning routine. At first, you might feel tired when you wake up, but as your body adjusts to your routine, you’ll start to wake up naturally, and the alarm will act as a backup.
  3. Exercise and get outside during the day: Our circadian rhythm responds to daily time cues known as ‘Zeitgebers’ which provide feedback to the body’s cells on what time of day it is. Exercise and natural light are potent Zeitgebers and can help your body’s hormonal balance to help a healthy sleep routine. Accessing the outdoors and exposing yourself to natural light in the morning is also a potent Zeitgeber and may help boost your energy levels for the day.

Key points:

  • Our body’s cells function within our circadian rhythm. This is determined by our exposure to night and day and has evolved to support our survival.
  • A regular bedtime routine can ensure we stay in tune with our circadian rhythms and support our sleep/wake cycle.
  • Research on maternal mothers has found that a regular bedtime routine improves sleep quality and overall mood and reduces nighttime awakenings in infants.
  • Setting a regular bedtime, wake-up time, and exercising outdoors in the morning during the day are great ways to help your sleep routine.

2) Avoid technology before bedtime

There are two key reasons why avoiding technology before bedtime can be an effective strategy for improving sleep:

  1. Blue light (emitted by phones and screens) has been shown to disrupt sleep physiology.
  2. Stimulating activities such as email and social media before bedtime have also been shown to interrupt sleep quality and duration.

Blue light stimulates sensors in the eye to send signals to the brain’s internal clock. This keeps us bright and awake during the day. However, if we’re exposed to it at night, it can ‘trick’ our brain into thinking it’s light outside when it’s time for sleep.

Light also helps to control the release of our sleep hormone called melatonin. When we see the light during the day, melatonin production is inhibited. When there is no more blue light at night, melatonin levels in our blood begin to rise, causing us to feel sleepy.

Modern society’s most common forms of blue light exposure that might interrupt our sleep hygiene are smartphones, TVs, and computer screens.

But it’s not just blue light that can disrupt sleep; it seems that the combination of blue light and stimulating activities before bedtime, such as using social media, email, or surfing the internet, also seem to affect the quality of our sleep.

A cross-sectional study investigated the link between electronic screen use before bedtime and sleep quality and duration. The results indicated that the more time spent on electronic screens before bedtime, the poorer the sleep quality and the lower the sleep duration. This association was more robust if the individuals were on social media or surfing the internet.

Recent research suggests that the impact of technology use on sleep has to do with a disruption in sleep physiology and the release of essential hormones that regulate our sleep-wake cycle, such as melatonin.

A recent study investigating technology’s effects on sleep randomly assigned 14 participants into three groups with different activities before bedtime: 

  1. 90-minutes on a smartphone without a blue light filter.
  2. 90-minutes on a smartphone with a blue light filter.
  3. 90-minutes reading a book or other printed material.

Interestingly, the study found that the group without the blue light filter spent less time in deep sleep, while the groups with the book and a blue light filter spent a similar time in deep sleep. Suggesting that a blue light filter can mitigate some of the effects of technology use before bedtime.

However, the smartphone groups had dysregulated melatonin and cortisol levels compared to the book group. Suggesting that technology use with or without a blue light filter may disrupt the hormonal balance essential in regulating our sleep-wake cycle.

But it should be noted that this was a small study, and this area of research is still in its infancy, so there’s still a lot we don’t yet know about the impact of technology on sleep.

What we do know is that there does seem to be an effect of technology use on our sleep – particularly stimulating activities like social media and email – and it’s a sensible approach to switch to more relaxing activities before bedtime, such as:

  • Reading.
  • Journalling.
  • Meditation.

Key points:

  • Technology use seems to disrupt the quality and duration of our sleep through the effects of blue light and stimulating activities such as social media, email, and surfing the internet.
  • Observational studies have shown associations between the use of technology and poorer sleep quality and duration.
  • A recent clinical study suggests that this relationship might be explained by the effect of technology use on the balance of critical hormones cortisol and melatonin.
  • Reading, journaling, and meditation are all calming and effective ways of winding down before bedtime.

3) Be mindful of your caffeine intake

Caffeine is a natural stimulant that activates our central nervous system to improve mental performance and increase alertness. This is why you often feel that ‘boost’ or caffeine ‘buzz’ after your morning coffee.

Individual responses to caffeine will vary depending on many factors, such as genetics and current caffeine intake.

How does caffeine affect our sleep?

Our level of sleepiness is primarily influenced by the accumulation of a chemical called ‘adenosine’ in our brain.

Adenosine causes drowsiness and regulates our circadian rhythm, the 24-hour biological cycle that influences many internal functions. Some experts refer to adenosine as ‘sleep pressure’ and the circadian rhythm as our ‘wake drive’.

Caffeine can temporarily block the adenosine receptors in our brain, meaning we can’t feel the sleep-inducing effects of adenosine. This results in us remaining alert and having difficulty falling asleep.

The relationship between coffee and caffeine consumption on sleep has been demonstrated in a recent systematic review which analysed 58 studies investigating the effects of caffeine on sleep.

The studies consistently showed altered sleep quality with higher caffeine intake. Although, it’s noteworthy that individual responses to caffeine will vary greatly.

How long does caffeine stay in our system?

The impact of caffeine on our sleep will depend on how we individually process it, how much we have, and how close to bedtime we drink it. However, research has shown that the average half-life of caffeine is about 5 hours, which means that it takes 5 hours for our body to process and get rid of half the caffeine in our system.

So if we drink a coffee after lunch at 2 pm, approximately half of the caffeine will still be in our system at 7 pm and a quarter at midnight. It’s believed that the caffeine from one coffee could take between 24 and 36 hours to leave our body entirely.

However, this will depend on the individual. How we respond to caffeine will vary from person to person. So, while some people can clear caffeine quickly, others may find it hanging around in their system longer – so it’s important to reflect on your individual response to consuming caffeine.

The time caffeine stays in our systems suggests that when we consume caffeine is essential.

A clinical trial in 98 adolescents showed that increased caffeine consumption was associated with poorer sleep quality and short sleep time. However, these results were primarily driven by afternoon and evening consumption.

Because of this, we recommend enjoying your caffeinated drinks before midday and switching to water and caffeine-free hot drinks such as herbal teas or decaf in the afternoon and evening.

It’s also been suggested that delaying your caffeine consumption by an hour or two after you wake up might help you avoid your energy levels dipping later in the day.

This recommendation is based on the circadian release of cortisol in the morning, which provides a natural stimulant so your body doesn’t need a double dose of stimulation, which might result in a more significant decline later.

Caffeine can decrease fatigue and improve focus and alertness. But while caffeine can be helpful, it impacts our sleep quality, so it’s essential to be mindful of when and how much caffeine we’re having – particularly if improving fertility is a goal.

Caffeine and fertility

While there are limited studies investigating the impact of caffeine on fertility, observational studies have shown an association between excess caffeine intake and fertility.

These studies suggest that while a moderate caffeine intake seems to have a neutral impact on fertility and your chances of pregnancy, consuming more than 300mg daily (around 3-4 large cups a day) may reduce your chances of conceiving by 17%.

In contrast, other observational studies found no association between caffeine intake on IVF outcomes.

Unfortunately, as these studies are observational, it’s difficult to determine a cause-and-effect relationship between caffeine and fertility. Caffeine consumption could be linked to other lifestyle behaviours such as smoking, alcohol intake, and diet.

Reassuringly, a study using plasma markers of caffeine intake (a more reliable measurement of caffeine intake than self-reported intake used in the studies described above) found no association between caffeine intake and fertility.

This is to say that caffeine might not directly affect fertility, and you shouldn’t be overly concerned about consuming it. However, it’s possible that it could indirectly impact your fertility by interrupting your sleep.

Key points:

  • Caffeine is a natural stimulant that triggers our central nervous system to improve mental performance and increase alertness.
  • However, it can impact our sleep quality because it can block adenosine receptors in the brain, meaning we’re unable to feel the sleep-inducing effects of adenosine.
  • Caffeine has a half-life of around five hours, which means if we’re having caffeinated drinks in the afternoon, there may still be residual caffeine in our system at bedtime. 
  • However, there is great variability in the individual responses to caffeine. 
  • If you’re currently consuming a large amount of caffeine, we’d recommend gradually reducing your intake and monitoring the positive benefits of this on your sleep quality.
  • Caffeine doesn’t appear to directly harm your fertility, but it might indirectly affect it due to its effects on sleep quality.

Take home message

Sleep is often defined as the foundation at which all other lifestyle habits can prosper. Without a healthy sleep routine, you’ll likely feel poor sleep’s physical and psychological effects.

Female fertility is also an area that sleep can impact via worsening insulin resistance, cortisol levels, and chronic inflammation.

You’ll likely improve your sleep quality and duration by having a consistent sleep routine, avoiding technology before bed, and being mindful of caffeine intake. Over time, this will positively affect your fertility and chances of a successful pregnancy.

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