Constant light causes harm to head and heart

Chris interviewed the University of Warwick's Francesco Cappucio about the health impacts of light pollution...

弗朗哥- - - - - -Light is the most important environmental cue that we have for synchronising our circadian rhythm. So any change that happens in the light-dark cycles will cause changes in the way our biological clocks work, and therefore will affect our sleep patterns in terms of quantity and quality.

Chris - And what's the evidence that, if you have those sorts of disturbances, the health impacts are negative?

弗朗哥- - - - - -The epidemiology of sleep in large populations has clearly shown that disturbances in terms of quality and quantity, so deprivation and also the fragmentation, are associated with the short term effects that we may all know and recognise: reduced alertness, reduced performance, low mood. But, also, more worryingly, now we know there are long term effects, and the long term effects are quite serious. We go from an increased incidence of obesity, high blood pressure and diabetes, to a more significant increase in fatal and nonfatal heart attacks and strokes, not to mention in mental health, depression, anxiety. And there is some evidence now to link disruption of sleep to some forms of cancers like breast cancer and prostate cancer.

Chris - Can we causally link that? Do we know, for example, that light pollution is causing the dysregulation of our body clocks and that is causing these diseases?

弗朗哥- - - - - -In terms of long term conditions, they can only be taken from experimental studies that have a shorter duration. But, if you manipulate, for instance, a sleep duration or you disrupt sleep in different ways, you can have reversible cardiometabolic and functional effects which, if sustained, would lead to serious conditions. We know that those effects are reversible when we change the disruption of sleep, so there is a very direct link between how much sleep is reduced in terms of quantity or is disrupted and the entity of the cardiometabolic, and also mental health issues that you find later on.

Chris - In these contexts, what do we actually call light pollution then? What do I need to be exposed to to cause these sorts of disruptions and therefore put myself at risk of the sorts of conditions that you've been outlining?

弗朗哥- - - - - -The importance of light in regulating sleep is quite complex. We have some biological clocks in our brain, the kick, to give us a day, night cycle, but they're not exactly 24 hours. We have a system through our eyes that detects day and night in order to tell the body clock to resynchronise every day to the 24 hours which is our conventional day that we have created as human beings. Now, that light that eventually comes to the body will stop one hormone called melatonin, which we call the sleeping hormone. And when it gets darker, the eye transfers that message. So the melatonin goes up and we tend to fall asleep. And vice versa; when daylight starts in the morning, the melatonin shuts down. So these are mainly affected by what we call blue light. The blue light has the effect of day, has an intensity and spectrum very similar to the sun. Whereas a red light, which is of less energetic light with a longer wavelength, is more conducive to sleep or dozing off. So, in reality, we need to avoid, during the night any light which is bright (is blue, has high intensity and spectrum.) I'm afraid we have many lit environments at night which have very bright blue light, and that can obviously disrupt sleep in the people exposed to it on a regular basis.

Chris - So is one mitigation that we either dissuade people from exposing themselves to these blue lights - because television screens these days, laptop screens, mobile phones, screens, these things are on all the time and we're all deluged in this light. We're all disrupting our body clocks then. Is it just that we've got to turn those things off or are there other ways that we can mitigate this so that they don't impact on our sleep in the same way or to the same extent?

弗朗哥- - - - - -这是非常重要的。首先, let me give you two or three numbers. In 2008, estimates were that 50% of the human population now lives in urban areas, and by 2050 it's estimated that more than 90% will be urbanised living in cities. Now, when we work out how much time we spend indoors in cities, at the moment it's nearly 80% and one third is spent in our bedroom. So when we get these numbers, we understand that the first thing is the indoor activity of light has to be regulated so that it is conducive to maintaining our day and night cycle. Otherwise, we'll always be awake. There are rules for individuals that they need to follow. And definitely not having a screen in the room is the first thing, particularly if it projects very blue high intensity light. But also we need to understand that most of the indoor activity happens in offices, in schools and, in particular, in hospitals. I have experience where being in a hospital at night is terrible because the lights are on all the time and patients can't sleep. Therefore, there is an issue between awareness and behavioural change. I would put sleep and light pollution and other problems within the domain of public health and policy where I think there needs to be more societal change. For instance, architects and planners at the moment might consider lights using the the visual performance type of problem. They don't consider what the non-visual effects are, which is exactly what we're talking about.