ARE YOU GETTING ENOUGH LIGHT? ENOUGH DARK?

Have you noticed the longer, lighter days? Isn’t it lovely? But are you spending sufficient time outdoors? Or in a sunny spot? Are you turning off Netflix/your laptop/your phone when darkness falls?

If you are, bravo! If not, you might want to read on. There’s a fair bit of science here, so scroll to the bottom if you’re only interested in our tips!

Last week I became immersed in a Dutch study investigating the effects of too much light at night and too little light during the day. After a long, particularly gloomy winter, this felt particularly important.

It was a small study, but rigorously carried out on an older population (aged between 45 and 75) of men and women with type 2 diabetes.  As the authors noted raised blood glucose and insulin levels affect us more as we age. The average age for the onset of diabetes is now 45, but falling rapidly. And yes, diabetes can kill.  But this post isn’t about diabetes – it’s about the hidden price of a life lived in artificial light.

The study from Maastricht University Medical Centre confirmed several earlier studies while also hinting at other physiological complications caused by too-much-evening-light and too-little-daytime light. It didn’t touch on depression or breast cancer, two other conditions linked to artificial light at night (catchily known as ALAN).

We all know that too much evening light (especially when it’s blue light) halts our body’s production of sleep hormone, melatonin.

We also know that a blast of morning light (within an hour of waking) sets our circadian clock.  If you’re new to the blog, here’s a quick refresher on why morning light is so important: When light hits the retina, a signal goes to a part of the brain called the suprachiasmatic nucleus, a tiny spot deep behind our eyes which coordinates our body’s rhythms. Morning light tells us to wake up, but it also tells our internal clock to prepare our bodies for later sleep (usually 15-18 hours later, depending on your genes).

Scientists are still unpicking how our circadian clock works. But as this Dutch study reveals, defying our natural rhythms could have greater consequences than disrupted sleep.

The study found that shifting light patterns had dramatic results on a range of health measures. Too little light during the day and too much at night did oh-so-much more than suppressing evening melatonin levels and reducing subsequent sleep. It affected participants’ metabolism, their glucose levels, their weight, even their blood pressure – and, by implication, their hearts.

When participants spent more of the day in bright light and the evening in dim light, they had lower blood glucose levels, a faster metabolism during sleep and more efficient energy consumption after their evening meal.  Put simply, their bodies worked more efficiently and effectively after a day spent in light and an evening spent in gloom – regardless of what they did or ate during that time.

When the situation was reversed (artificial light during the day and the evening, the way most of us currently live), their bodies’ reverted to their usual diabetic pattern, with raised blood glucose levels and less efficient metabolism during the evening  and a metabolism that slowed down as they slept. Regardless of their diet and exercise.

As the researchers pointed out, the smallest shifts in how our bodies expend energy can dramatically affect us, particularly when they happen over long periods of time.  Years of sitting indoors (where no amount of bulb wattage can ever compete with outdoor light) and evenings spent on a screen (TV, laptop, iphone) is how obesity and metabolic disease can creep up on us.

So why does light exposure do this? No one knows, but the Dutch authors of this study think the answer might lie with our gut. They speculate that the trillions of gut bacteria living within us also need the age-old rhythms of light days and dark nights in order to properly digest our food.

So, to summarise, artificial light during the day and evenings, cuts our levels of melatonin (also vital for ageing well), as well as messing with our digestion, raising our evening blood glucose levels, slowing down our metabolism and making us overweight.

You’d be forgiven for thinking this was quite enough damage. But it wasn’t.  The researchers also noted changes to the participants’ skin temperature.  Dim, artificial light during the day led to falling skin temperature, which was compounded after an evening in bright light.

Again, this was reversed when participants had more light during the day and less in the evening. On these occasions, skin temperature was more variable during the day, and higher in the evening.

Why does this matter? And what does it indicate?

When the temperature of our skin falls, our veins constrict. And when the temperature of our skin rises, our veins dilate – in other words our skin temperature is intimately bound up with our vascular system, which is intimately bound up with the pressure of our blood, which is intimately bound up with our heart.  Light seems to trigger daytime fluctuations in temperature that are good for our heart.  Meanwhile, warmer skin at night means more dilated veins, lower blood pressure and a heart that is well-prepared for sleep.

Meanwhile, as I write, a new study has dropped into my in-box confirming a few other consequences of too much artificial evening light. In this study (which involved ten young men, so perhaps not quite so relevant to us age-wellers) participants were exposed to either three hours of bright evening light or three hours of dim evening light. They slept in a metabolic chamber where they were repeatedly tested over a two-week period.  Those exposed to dim light (less than 50 lux) produced 63% more melatonin in the hours before bed.  But, importantly, other things happened in their bodies too. They were better able to metabolise fat, not only as they sat in the soft light of a lamp but as they slept.  Those who’d spent 3 hours beneath the equivalent of bathroom LED lights had less efficient metabolic (fat-burning) rates when they (eventually – as nodding off took longer) slept.  Which confirms other reports linking ALAN to obesity and Type 2 diabetes.

I hope this post will make you hurry outside (if it’s daytime, although as I write it is very windy indeed in the UK!) or turn off your screen/TV/LED lights (if it’s night-time).  But there are other simple things you can do:

• Always get 10 minutes of outside light ideally within an hour of waking.
• Be outside as often as you can… put on a coat and take your cuppa to the front doorstep or the office balcony.
• Put your desk/chair in front of a window.
• Where possible open that window – glass cuts out 50% of the blue (morning) light we need to set our internal clocks.
• When the sun moves to another part of the office/house, follow it.
• Expose your eyes – ideally while moving, a walk is perfect – to late afternoon light, helping your clock adjust for the evening.
• Only use table lamps (with yellow/amber or red bulbs) or candles in the evening. Keep the lights dim, especially bathroom lights which are ridiculously white-bright! I clean my teeth in the dark now (standing on one leg, of course!)
• Turn the screen brightness down on all your devices in the evening or use a programme like f.lux.
• Turn screens off at least an hour before you want to sleep.  Read a (proper) book or listen to music instead. A recent study found that reading a paper book is substantially different to reading on an iphone, with superior benefits for both brain, body and comprehension.
• Turn off security lights that threaten to stun (you or others) when activated. I met a retired policeman last week who told me, with complete confidence, that security lights help rather than hinder burglars.
• Wildlife also needs night-darkness so turn off unnecessary garden/exterior lights.

If you have any other tips, please leave a comment… We’d love to hear. Lastly, to keep my publisher happy, I need to shamelessly plug (apologies) my new book, 52 Ways to Walk. It was published yesterday and includes lots of ideas for ambles and strides to set your circadian clock, to prompt melatonin production, to improve balance, to work your memory, to improve your night vision and plenty more besides, including tips on how to benefit from a windy walk!

Annabel