Chasing the Sun: The astonishing science of sunlight and how it can help you survive in a 24/7 world

By Anna Wirz-Justice, PhD

A science journalist’s guide to the modern science of light, and how it affects us

It’s about time! In the dark days of winter, the science writer Linda Geddes has published a timely book about the importance of sunlight for our health and well-being. She has travelled far and wide, and read deeply, to translate the new research findings of the last two decades into a comprehensible and enjoyable text.

Our expanding knowledge of the effects of light in humans has had major consequences: for example, the discovery of a novel blue-sensitive photoreceptor in the eye, transmitting light information to so-called “non-visual” functions of the brain (such as circadian rhythms, sleep, alertness, mood and performance), has dramatically affected the lighting industry and its norms. Body clocks, ticking at the genetic level, orchestrate a myriad of rhythmic physiological, biochemical, and behavioural functions that need to be in synch for well-being and health. And light via the eyes is the major synchroniser.
The new science of sunlight and how it shapes
our bodies and minds

By Linda Geddes
Illustrated, 256 pp. Wellcome Collection. $19.90.


Geddes reviews the way these clocks can change, for example, becoming delayed or advanced as in adolescence and old age, or the individual chronotype of owl or lark. These clocks can also become misaligned with inflexibly early school and work times, shift work, and the time changes of jet lag. Clearly, our 24/7 society, with its continuous availability of artificial lighting, differs from the naturalistic sleep-wake and light-oriented behavior seen in the Amish, or camping. This difference reminds us of the archetypal link to dawn and dusk that we have lost.

Try to live a few weeks without artificial light, following the daylength, as the author did one winter – difficult socially, but rewarded by better sleep, mood and alertness. ”Although few of us would be prepared to spend our evenings in candlelight on a permanent basis, spending time outdoors during the daytime may be something more of us can work into our lives.” An hour a day keeps the doctor away could become a behavioral prescription for daylight exposure.

The treatment of Seasonal Affective Disorder by light was based on the neurobiology of seasonal rhythms. Light therapy is now widely accepted as a treatment in an increasing number of diagnostic categories – non-seasonal and bipolar depression, and many sleep disorders, for example. Daylight awareness has entered the practice of architecture beyond the aesthetic and functional: “…a better understanding of how our internal clocks affect our minds and bodies could markedly improve health outcomes in psychiatric, neonatal and post-operative wards, and in care homes.” Geddes covers the older history of sunlight cures, and UV rays as antibiotic, as well as the need for daylight to prevent myopia in children, and to ensure Vitamin D synthesis when the skin is exposed.

Light, sleep and timing: these are three basic things that have the potential to transform health care.” This is an excellent introduction and guide to the modern science of light and the human for the general public.
ANNA WIRZ-JUSTICE, PhD, is a member of CET’s Board of Directors.