How sunlight strengthens our minds and bodies

Our biology is set up to work in partnership with the sun. In every one of the cells in our bodies, there ticks a molecular clock that regulates the timing of almost all our physiological processes, from sleep, to the activity of our immune cells, to the release of chemical signals controlling our metabolism, appetite and mood. These circadian rhythms are kept synchronised to the external 24-hour day through the action of light hitting a group of cells in the back of our eyes. In the modern era, with 90% of our daytimes spent indoors and our evenings spent bathed in artificial light, these rhythms are being disrupted and our ancient relationship with the sun forgotten.

During 2017 and 2018, I travelled to the USA, Scandinavia, Germany and Italy on a Churchill Fellowship to learn how scientists are rediscovering sunlight as a means of improving our health and wellbeing.

In Denmark, patients with severe depression are being encouraged to improve their mental health by keeping regular daily schedules and getting outdoors as much as possible. In Italy, psychiatrists are taking things a step further with their treatment of bipolar patients: a combination of sleep deprivation and bright light therapy aims to kickstart patients’ sluggish circadian clocks and lift them out of depression.

On my travels I also came across examples of artificial light being used as a substitute for sunlight. In care homes in the USA and Denmark, people with dementia are being exposed to more natural cycles of light and dark thanks to the installation of so-called human-centric lighting. This mimics the rising and setting of the sun, through changes in colour and intensity over the course of 24 hours. As a result, levels of agitation and night waking have decreased.

My Fellowship also introduced me to people who have an unusual relationship with light, from a submariner who can go months without seeing the sun, to an Amish community that lives off-grid and as a result are exposed to far lower levels of light at night than most Westerners.

Finally, I visited a spa town in Germany called Bad Kissingen, which has rebranded itself as the world’s first Chronocity - a place where people’s internal body clocks are seen as being as important as external time, and sleep is sacrosanct. The local secondary school is considering changing its teaching hours to accommodate the later sleep preferences of its students, and outdoor lessons are encouraged to strengthen students’ circadian clocks. Meanwhile, the town’s tourist office now offers flexible working to its staff, meaning that night-owl employees can start work later and therefore get more sleep.

You can read more about my adventures while researching this issue in my new book, Chasing The Sun: The new science of sunlight and how it shapes out bodies and minds, which is out now. Extracts from the book are also appearing in the Daily Mail and The Guardian. I will be giving talks on my research in London, at the Wellcome Collection on 31 January and at the Royal Institution on 25 March.

Today our relationship with sunlight is weakened, but not broken. Artificial light, which has done so much to erode this relationship, may yet provide some solutions – but we need to learn how to harness it effectively and when to avoid it. I hope that, in this respect, my book will provide some pointers.

Listen to Linda speak on Start the Week with Andrew Marr