Chasing the Sun: How the Science of Sunlight Shapes Our Bodies and Minds – Linda Geddes

Thoughts: I found this book browsing the stacks at the Kitchener Public Library, and I think it got mis-catalogued somewhere along the way - a book about the effects of sunlight on our health, I found it next to books on physics and astronomy. It’s not long, it’s full of practical information, and it strikes a good balance between outlining the current state of research and offering anecdotes and case studies for memorability. As someone who until recently has tried to avoid direct sunlight in an effort to minimize my chances of eventually developing skin cancer, I wish I’d come across it several years ago! Based on reading it, I’m going to start taking a more nuanced approach (something along the lines of avoiding sunlight during the summer and while the UV index is high - perhaps 4 or greater - while seeking it out during the fall-winter-spring and when the UV index is 3-ish or lower).

(The notes below are not a summary of the book, but rather raw notes - whatever I thought, at the time, might be worth remembering.)

Geddes, Linda. 2019. Chasing the Sun: How the Science of Sunlight Shapes Our Bodies and Minds. Pegasus Books.

Introduction

1. The Body Clocks

• 38: Human groups likely benefitted from a having a range of chronotypes, ensuring at least one member of the group was awake at all times. “[David] Samson believes that this phenomenon could also explain why humans are so long-lived. ‘we’re calling it the poorly sleeping grandparent hypothesis,’ he says. Previously, researchers have suggested that the reason so many people live long past reproductive age is because of the survival advantage to the group conferred by grandparents helping with child-rearing. Now it seems that there may be an additional advantage: keeping look out.”

2. The Body Electric

• 48: book mentioned: Why We Sleep by neuroscientist Matthew Walker
• 55: “In the West, we spend our daytimes in the equivalent of twilight, and then keep the lights switched on well after sunset.”
• 61: re: getting outside during the winter: “I was reminded of something a Swedish friend used to say: there’s no such thing as bad weather, only inappropriate clothing.”
• 63: “A recent German study… suggested that exposure to bright light in the morning boosted people’s reaction speed and maintained them at a higher level throughout the day—even after the bright light had been switched off. It also prevented their body clocks from shifting later when they were exposed to blue light before bed. ¶ This is good news because it suggests that we may not need to completely forego electric lighting in the evenings in order to reap the benefits of improved sleep and daytime performance. Mounting evidence suggests that just by spending more of our daytimes outdoors or exposed to brighter indoor lighting we may achieve the same result.”

3. Shift Work

• 68: Sleep deprivation (in this study, sleeping 5 hours per day) causes problems like reduction in insulin sensitivity, increase in inflammation, but these effects are particularly pronounced when combined with an irregular sleep schedule.
• 73: Different organs in our body each have their own circadian clocks. There exist mechanisms to help them remain synchronized, but they can fall out of sync (a common way this can occur is by eating at a different time than usual)
  • 83: also e.g.: exercise when you’d normally be going to bed can shift the circadian rhythms of muscles, lungs, liver, but doesn’t affect the master clock in the brain
• 75: “Various animal studies had suggested that melatonin might have anti-cancer properties. Aside from its links to the circadian system, melatonin also helps to mop up reactive oxygen species, or ‘free-radicals’, which are generated by normal metabolism and can damage DNA and other cellular components. If melatonin is suppressed because of regular exposure to bright light at night, it seems likely that more cancer-causing mutations will occur.”
• 82: “It… seems to be the case that more energy is used to process a meal when it’s eaten in the morning, compared with later in the day, so you burn slightly more calories if you eat earlier…. It’s still unclear how much of a difference this would make to overall body weight. For now, the take-home message is that it is probably healthier to breakfast like a king, lunch like a prince and eat dinner like a pauper—but we don’t yet entirely understand why.”
• 83: takeaway: if you can, follow a regular schedule, including seeking bright light during the day (esp. the morning), avoiding light in the evening.

4. Doctor Sunshine

• 107: Exposure to bright daytime light seems to prevent against the development of myopia in children (more exposure to bright light later in life doesn’t seem to reverse it, however)

5. Protection Factor

• 122-123: People who actively seek out exposure to sunlight (e.g. people who habitually sunbathe) tend to have longer life expectancies than those who avoid sunlight. The increased risk of developing skin cancer is more than offset by a decreased risk of developing cardiovascular disease and other non-cancer diseases. (also, sun-seekers who develop skin cancer have much more likely to recover from the cancer, compared to sun-avoiders who develop skin cancer)
• 124: “Most important of all is to avoid sunburn”
• 125-126: exposure to sunlight triggers the release of endorphins, which could be a means (sunlight -> more endorphins -> relaxation, less stress, lower blood pressure) by which sunlight exposure protects against heart disease. It also helps explain why it feels good to be in the sun

6. A Dark Place

• 143: trials have found that Cognitive Behavioral Therapy - helping people reframe their thoughts about wintertime - is at least as effective as light therapy in countering Seasonal Affective Disorder. Decreased light levels do contribute, but if you think winter will make you miserable, it probably will.

7. Midnight Sun

8. Light Cure

9. Fine-tuning the Clock

• 181: to minimize jet lag: the relevant detail is what time your body thinks it is (i.e. the time zone you are leaving).
  • If you are travelling east, avoid light from 6pm until 6am, and seek light from 6am until 6pm, in the time zone you are leaving, which will tend to advance your body clock.
  • If you are travelling west, avoid light from 6am until 6pm, and seek light from 6pm until 6am, in the time zone you are leaving, which will tend to delay your body clock.
• 186-187: physical performance (think sports) varies throughout the day
  • 187: “Exercising in the early morning could carry a greater risk of injury, so it’s worth spending more time warming up at that time of day.”

10. Clocks for Society

• 198: studies where schools / high schools have experimented with starting much later in the morning: “almost unanimous support for it among students, teachers, and parents. Despite parents’ fears that they’d use it as an excuse for going to bed later, the [teens’] bedtimes remained relatively unchanged, but they slept later in the mornings and got more sleep overall. Students said they felt less tired during the day and thought their grades had improved, while teachers noticed fewer pupils with their heads down on their desks and reported that the children seemed more engaged and focused. School attendance also improved.”

Epilogue

Acknowledgements

• 213: Recommended books about circadian rhythms
  • Russel Forster and Leon Kreitzman: Rhythms of Life
  • Russel Forster and Leon Kreitzman: Circadian Rhythms: a very short introduction
  • Steven Lockley and Russel Forster: Sleep: a very short introduction
  • Till Roenneberg: Internal Time
  • Michael Terman: Reset Your Inner Clock
• 213: Recommended books on humans’ historical relationship with sunlight
  • Ronald Hutton: Stations of the Sun
  • Mike Williams: Prehistoric Belief
  • Richard Cohen: Chasing the Sun