On average, you will spend 26 years of your life sleeping and 7 years trying to sleep.. that’s a total of 34 years.. it’s probably about time I invest in a good mattress! But, it’s not only all about the mattress of course, you can improve your sleep hygiene in many ways, whether it’s your nighttime routine, nutrition or exercise habits. And, once you’ve cracked it, your immune system will thank you for that extra support.
I’m going to use a little science jargon to explain how a good night’s sleep plays an important role in helping support the normal function of your immune system.
In this blog, I’ll explain how sleep deprivation impacts both your hormones and your immune system since these are highly interconnected. And when I say sleep deprivation this means getting six hours or less of sleep per night. What may surprise you is that the impact of this on your health can be seen even after just one night of lost or interrupted sleep – this shows how consistency from day to day is key when striving for good sleep hygiene.
Right, let’s dive into the science!
The 2 hormones we are going to focus on are cortisol and melatonin, both of which are involved in our sleep-wake cycles. Cortisol is involved in many different processes, including metabolism, inflammation, immunity and blood pressure. Once you fall asleep, your brain sends signals to your adrenal glands which sit on top of your kidneys. These signals tell your adrenal glands to begin secreting cortisol into your bloodstream and these levels rise until they reach a peak at around 8 or 9 am. Levels are highest at this time because your body is signalling to you to get up and get going – your energy, memory and immunity are all generally functioning at their best at this time. Cortisol is also called the “stress hormone” because we tend to also produce more when we are under stress which is a survival mechanism with benefits. But when this stress becomes chronic and long-term, our body is unable to relax whilst cortisol levels remain high. One example of a culprit that causes this is disordered sleep. If your sleep is interrupted or shortened, then this can cause cortisol levels to peak at an abnormal time but also stay high for longer. Cortisol is normally anti-inflammatory but when there’s too much of it for too long then it can have pro-inflammatory effects and your immune system becomes incapable of reacting properly to infections. And the older we are, the less capable we are of getting our cortisol levels back to baseline levels after experiencing chronic stress.
Another important hormone involved in your sleep-wake cycle is melatonin. Its levels peak at the opposite time to cortisol, so they are highest when you are about to fall asleep. Your brain depends on sunlight to know when to start producing this hormone – so as darkness approaches, levels increase. This is ultimately an issue for night-time shift workers because, not only are they exposed to artificial light during the night but, they are also exposed to less sunlight on a daily basis which severely disrupts their sleep-wake cycle. Low and disrupted melatonin levels impact the anti-inflammatory and antioxidant activity of melatonin and, similarly to cortisol, this impacts the function of the immune system. Low melatonin levels also cause oestrogen levels to increase, which could explain the high rates of breast cancer in female night-time shift workers.
Because both cortisol and melatonin impact so many of our bodily processes, having their levels disrupted will wreak havoc with our health.
Now if we look at some of the key players within your immune system, studies have shown that one night of sleep disturbance causes a dramatic decrease in the number of Killer T-cells but they also become less efficient at latching onto infected cells. This ultimately means your immune system is less capable of responding to infections. In addition to this, the levels of pro-inflammatory signals in your body increases after a night of poor sleep. So this doesn’t bode well for your body’s ability to defend itself and keep inflammation levels within the normal range.
If you’re averaging 6 hours of sleep per night over a period of time then you are 4 times more likely to become ill after being exposed to viruses. And, even if you do get the flu shot for the influenza virus, for example, your immune response is half of what it should be if you had the shot when you were not sleep-deprived.
Poor sleep also increases your overall risk of developing cancer because your immune system is unable to mount a proper response to cancer cells – this is likely why night-time shift workers have higher rates of cancer compared to normal shift workers. The World Health Organisation has even gone so far as to classify night-time shift work as a probable carcinogen.
We have all experienced disrupted sleep, whether it’s an all-nighter we pulled for that college essay, partying all night, looking after a newborn.. but it often pokes it nasty little head when we don’t ask for it, especially as we age. It can also become part of a difficult cycle to break when it appears in conditions such as depression and chronic stress. But there are numerous ways in which we can indirectly tackle disordered sleep such as by improving our exercise and nutrition habits. This will ultimately help support the functioning of our immune system by enhancing the efficiency of our T-cell responses, and this will improve our overall health.
Written by Dr Elisabeth Thubron - Head of Science & Research