Don’t delay your bedtime for this important sleep reason, says doctor

You’re missing out on this crucial stage of sleep if you delay your bedtime

Woman feeling tired & not able to sleep
(Image credit: Cottonbro Studio / Pexels)

Do you struggle to fall asleep at night? Or maybe you can’t resist staying up to watch one more episode of your favourite TV show. But while you might think it’s not a big deal to delay your bedtime, you could actually be missing out on a very crucial phase of sleep.

For viral sleep hacks (opens in new tab), many people are turning to TikTok where doctors like NHS surgeon Dr Karan Raj (opens in new tab) create content that offers medical advice, sleep tips and debunks health myths. In a recent video from Dr Raj (opens in new tab), he explains that by delaying your bedtime, you won’t just feel tired the next day but you could be affecting your hormone production and general health and wellbeing.

The phase Dr Raj is referring to is slow wave sleep. But what is it and why does it matter? Keep reading to find out.

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What is slow wave sleep?

Slow wave sleep (SWS) or deep sleep is a period of non-rapid eye movement (NREM) sleep which is characterised by high-amplitude low-frequency waves (opens in new tab). This stage of sleep typically happens during the first few hours of sleep and lasts between 70-90 minutes. In Dr Raj’s video, he explains that “the early part of the night is dominated by NREM sleep. This is important because NREM sleep includes the deeper restorative slow wave sleep that’s coupled with the biggest release of growth hormone in your 24 hours.”

The growth hormone (which is produced by the pituitary gland located at the base of the brain) is what fuels childhood growth and maintains your body’s organs and tissues throughout your life, according to Mayo Clinic (opens in new tab). Around 70% of this hormone comes from the slow wave sleep stage which is why it’s so important to make sure you’re not delaying your bedtime.

A snippet of a TikTok video from Dr Raj

(Image credit: Dr Raj / TikTok)

But why? Dr Raj explains that “as the night goes on, the ratio of NREM to REM sleep changes and you get progressively less NREM and more REM sleep. If you cut short your bedtime, you cut the short time you spend in slow wave sleep and so you get less of that growth hormone.”

And that’s not all – it turns out that as we get older, we start to get less slow wave sleep. “Into your 30s and 40s, the total amount of growth hormone release in 24 hours decreases as does the amount of slow wave sleep.” What this means is that by wasting time scrolling on your phone or staying up for an hour or more longer than you normally do, you’re reducing or cancelling out entirely the amount of growth hormone your brain releases and your body receives.

This hormone is particularly important for children and teenagers to continue growing but as you get older, a lack of this growth hormone is not only a sign of aging but it can affect your body fat, aerobic capacity (opens in new tab), and muscle and brain mass. As stated in his video, Dr Raj says that this is why it’s important to go to bed at a similar time every day, so you get every bit of that growth hormone.

In general, having a set bedtime routine is a sign of good sleep hygiene (opens in new tab), so you should be aiming to do this anyway, to ensure you have the best night’s sleep and wake up the next day feeling refreshed and motivated.

Bethan Girdler-Maslen
Acting Wellness Editor & Deals Writer

As T3's resident Shopping Expert and Deals Writer, Beth covers deals, discount codes, how to save money and seasonal holidays, including Black Friday, Cyber Monday, Amazon Prime Day, Boxing Day and Easter sales. Alongside her primary focus of deals, Beth is currently Acting Wellness Editor, covering all things sleep, yoga, relaxation and general wellbeing.


Having always been passionate about writing, she’s written for websites, newspapers and magazines on a variety of topics, from jewellery and culture, to food and telecoms. You can find her work across numerous sites, including Wedding Ideas Magazine, Health & Wellbeing, The Bristol Post, Fashion & Style Directory and more. In her spare time, Beth enjoys running, reading, baking and attempting DIY craft projects that will probably end in disaster!