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Understanding our circadian rythm for sleep and health


The cycle of sleep and wakefulness is one of the key human behaviours.

We spend about a third of our lives asleep and cannot survive without it.

When asleep, our brain memorises and processes information. Our body clears toxins and repairs itself, allowing us to function properly when awake.


Even short-term sleep deprivation significantly affects our wellbeing. Most of us begin to fall apart after just one night without sleep and after three nights of missed sleep, we are functioning way below par.


One study suggested that after 17-19 hours of staying awake, performance on cognitive tasks may be similar to having had too much to drink.

These effects worsen over time. The longest documented period of time without sleep of just more than 11 days prompted serious cognitive and behavioural changes, problems with concentration and short term memory, paranoia and hallucinations.

But while scientists have long understood the importance of getting enough sleep, the key part played by light exposure can sometimes be overlooked.


The reason light is so important is that it sets our circadian rhythm, or body clock, via specialised light sensors within the eye.

Our eye detects the light and dark cycle within our environment and adjusts the body's circadian rhythm so that the internal and external day coincide.

This is so powerful that that people who have very severe eye damagecan find their body clock is thrown off leading to sleep problems.


Without any access to light, the human body clock appears to drift, adding about half an hour on to its 24 hour cycle for each day of darkness.

Jetlag is the most obvious example of the effect light can have. Exposure to light in the new time zone helps reset our body clock to local time, telling us the right time to sleep.

In 1800, most people across the world worked outside and were exposed to the change from day to night.


Today, many of us miss out on these environmental cues as we work inside. Agriculture and fishing, for example, now make up just 1% of jobs in the UK

We have become a light deprived species, and this has far reaching consequences for the quality of our sleep, and consequently our wellbeing. The optimum amount varies from person to person, but we do know that our bodies need exposure to very bright light that the majority of indoor lighting does not provide.

One notable side effect is Seasonal Affective Disorder (SAD), a form of depression which is linked to lack of sunlight exposure.

And there are many other areas where lack of natural light has caused problems like shift workers, people in care homes or working long shifts in unnatural lighting.


The health consequences of smoking, alcohol and unprotected sex are well publicised, but the importance of sleep and the critical role played by light is arguably less well known.

Further research and greater awareness in this area could help individuals to make informed choices about prioritising their own sleep and getting enough sunlight.


Minimising blue light exposure before you go to bed, this actually blocks the majority of melatononin being produced (our sleep hormone) and try to get as much morning light as possible, as well as intervals throunghout the day, even just for a few minutes has shown to be beneficial, these are simple steps that could help most people to regulate and improve their sleep.


Tips to implement are-


Try and get outside whenever you can ideally first thing in the morning and as the sun sets without constantly wearing your sunglasses not only will your circadian clock benefit but you can also top up on much needed vitamin D.


Stay away from caffeine after lunch, caffeine is a huge stimulant and has lasting effects up to 5 hours or more.


Read a book in the evening instead of looking at your phone at least an hour before bed.


Get into a routine with a regular bedtime (ideally between 10-11am at the latest) and no laptop 'lapdances' in bed, leave your electricals out of the bedroom.

A regular waking time is also important, you may find after a while that you don't need an alarm to wake up.


We all have really busy lives and sometimes it's just not possible, but it realy is the backbone of health in my opinion and the way we are meant to thrive.





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