1. https://physoc.onlinelibrary.wiley.com/doi/full/10.1113/expphysi01.2012.071118.
2. Richard Cohen, Chasing the Sun: The Epic Story of the Star That Gives Us Life (Simon & Schuster, London, 2011), p. 292.
3. Q. Dong, ‘Seasonal Changes and Seasonal Regimen in Hippocrates’, Journal of Cambridge Studies, 6 (4), 2011, p. 128. https://doi.org/10.17863/CAM.1407.
1. At least, if studies in mice are to be believed. One recent study found that replication of the herpes virus was up to ten times greater if mice were infected at the start of their resting phase, compared to when they would usually be active; see http://www.pnas.org/content/early/2016/08/10/1601895113. Other studies have suggested that their vulnerability to food-borne pathogens is greater then as well; see https://www.cell.com/cell-host-microbe/pdf/S1931–3128(17)30290–1.pdf.
2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3022154/.
3. Peter Coveney and Roger Highfield, The Arrow of Time (Penguin Books, London, 1990).
4. Benzer was inspired by the work of Colin S. Pittendrigh – widely considered the founding father of circadian rhythms. He was the first to show that Drosophila larvae emerge from their pupa like clockwork, even when kept in constant darkness.
5. A ‘free-running period’ is the scientific term for the amount of time it takes someone’s endogenous or pre-programmed rhythm to repeat itself in the absence of environmental time cues such as light.
6. http://www.kentonline.co.uk/kent/news/lifelong-islander-harry-loses-ca-a49624/.
7. Most blind people can still determine the difference between light and dark, and where a light source is coming from. Total blindness is the complete lack of light perception.
8. https://www.tandfonline.com/doi/abs/10.1080/00140138708966031.
9. http://www.tandfonline.com/doi/abs/10.3109/07420528.2016.1138120. This study also found that the parents of ‘evening-type’ children reported more sleep-related challenges. Their kids were more likely to resist going to bed at night, to wake up in a negative mood, and to have conflicts with their parents.
10. David R. Samson et al., ‘Chronotype variation drives nighttime sentinel-like behaviour in hunter-gatherers’, Proceedings of the Royal Society B, 284 (1858), 12 July 2017, doi: 10.1098/rspb.2017.0967.
1. For more on the evolution of electric light, see Jane Brox, Brilliant (Souvenir Press, London, 2011), which is a great read.
2. Robert Louis Stevenson, Virginibus Puerisque, 1881.
3. Robert Louis Stevenson, Virginibus Puerisque, 1881.
4. Jim Horne, Sleepfaring: A Journey through the Science of Sleep (Oxford University Press, 2007).
5. Nicholas Campion, in discussion with the author. For more on this idea, see Campion’s preface to Ada Blair’s Sark in the Dark: Wellbeing and Community on the Dark Sky Island of Sark (Sophia Centre Press, Bath, 2016), p. xvii.
6. https://www.scientificamerican.com/article/q-a-the-astronaut-who-captured-out-of-this-world-views-of-earth-slide-show1/.
7. To learn more about this project, visit http://citiesatnight.org/.
8. https://www.extension.purdue.edu/extmedia/fnr/fnr-faq-17.pdf.
9. https://www.nature.com/articles/nature23288.
10. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4863221/.
11. Donald J. Trump, Think Like a Billionaire (Ballantine Books, New York, 2005), p. xvii.
12. For a more detailed description of how sleep shaped our evolution, and the role it plays in memory and emotional regulation, see Matthew Walker’s book, Why We Sleep (Allen Lane, London, 2017), pp. 72–77.
13. Russell Foster and Leon Kreitzman, Circadian Rhythms: A Very Short Introduction (Oxford University Press, 2017), p. 17.
14. http://www.cell.com/current-biology/abstract/S0960–9822(15)01157–4.
15. https://www.cell.com/current-biology/abstract/S0960–9822(13)00764–1.
16. http://www.cell.com/current-biology/fulltext/S0960–9822(16)31522–6.
17. For factories assembling electrical components, or other workplaces requiring perception of fine details, the HSE recommends an average illuminance of 500 lux.
18. http://www.sleephealthjournal.org/article/S2352–7218(17)30041–4/fulltext.
19. https://www.ncbi.nlm.nih.gov/pubmed/29040758.
20. https://www.ncbi.nlm.nih.gov/pubmed/28637029.
21. https://www.ncbi.nlm.nih.gov/pubmed/22001491.
22. http://www.sjweh.fi/show_abstract.php?abstract_id=1268.
23. http://www.sciencedirect.com/science/article/pii/S0165032712006982.
1. Arianna Huffington, The Sleep Revolution: Transforming Your Life, One Night at a Time (W.H. Allen, London, 2017).
2. Certainly, prolonged sleep deprivation appears deadly to rats: they die after approximately fifteen days of being kept awake – roughly as long as it takes for them to die without food. In the run-up to death, they lose their ability to regulate body temperature, develop wounds and sores on their skin and internal organs, and their immune system collapses.
3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1739867/.
4. Acute Sleep Deprivation and Risk of Motor Vehicle Crash Involvement (AAA Foundation for Traffic Safety, December 2016).
5. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4030107/.
6. Foster and Kreitzman, Circadian Rhythms, p. 19.
7. Study presented at the annual meeting of the Associated Professional Sleep Societies in Boston in June 2017, by Sierra B. Forbush of the University of Arizona.
8. Till Roenneberg, in discussion with the author.
9. Seth Burton, in discussion with the author.
10. https://www.ncbi.nlm.nih.gov/pubmed/10704520.
11. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0015267.
12. http://www.pnas.org/content/115/30/7825.
13. Richard Stevens, in discussion with the author.
14. https://www.ncbi.nlm.nih.gov/pubmed/8740732.
15. http://www.pnas.org/content/pnas/106/11/4453.full.pdf.
16. https://www.ncbi.nlm.nih.gov/pubmed/26548599.
17. https://onlinelibrary.wiley.com/doi/abs/10.1002/oby.20460.
18. Jonathan Johnston, in discussion with the author.
19. http://www.cell.com/current-biology/abstract/S0960–9822(17)30504–3.
20. https://www.sciencedaily.com/releases/2017/08/170815141712.htm.
21. https://www.ncbi.nlm.nih.gov/pubmed/22621361.
1. For further reading on the fascinating history of ‘sun cures’, I’d highly recommend Richard Hobday’s The Healing Sun: Sunlight and Health in the 21st Century (Findhorn Press, Forres, 1999).
2. Florence Nightingale, Notes on Nursing: What it is, and What it is not (CreateSpace Independent Publishing Platform, 2015).
3. https://www.ncbi.nlm.nih.gov/pubmed/15888127.
4. Hobday, The Healing Sun.
5. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3277100/.
6. Quoted in Joseph Mercola, Dark Deception: Discover the Truths about the Benefits of Sunlight Exposure (Thomas Nelson, Nashville, Tennessee, 2008).
7. http://www.jbc.org/content/64/1/181.full.pdf.
8. From Paul Jarrett and Robert Scragg, ‘A short history of phototherapy, vitamin D and skin disease’, Photochemical & Photobiological Sciences, vol. 3, 2017.
9. Victor Dane, The Sunlight Cure: How to Use the Ultraviolet Rays (Athletic Publications, London, 1929).
10. Quoted in Jarrett and Scragg, ‘A short history of phototherapy, vitamin D and skin disease’, 2017.
11. Quoted in Hobday, The Healing Sun.
12. https://www.thelancet.com/journals/lancet/article/PIIS0140–6736(16)31588–4/fulltext.
13. https://www.telegraph.co.uk/news/2018/01/12/no-light-end-tunnel-chelseas-new-1-billion-stadium/.
14. https://www.hindustantimes.com/delhi-news/in-a-dense-and-rising-delhi-exert-your-right-to-sunlight/story-zs0xLKVT8UKC05B5JfQi5M.html.
15. https://www.aaojournal.org/article/S0161–6420(07)01364–4/fulltext.
16. Ian Morgan, in discussion with the author.
17. https://www.ncbi.nlm.nih.gov/pubmed/26372583.
1. https://www.ncbi.nlm.nih.gov/pubmed/2003996.
2. https://www.newscientist.com/article/mg19325881–700-born-under-a-bad-sign/.
3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4986668/.
4. http://journals.plos.org/plosbiology/article?id=10.1371/journal.pbi0.1000316.
5. Besides multiple sclerosis, one of the most robust associations for these month-of-birth effects is for type 1 diabetes – another autoimmune disease; see https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2768213/.
6. These figures only apply to nations containing people of primarily European descent. For other nations, no association with latitude was found – but Europeans have a higher genetic risk of MS in the first place. See https://www.ncbi.nlm.nih.gov/pubmed/21478203.
7. Consistent annual data wasn’t available before this point.
8. https://www.karger.com/Article/Abstract/336234.
9. https://www.karger.com/Article/FullText/357731.
10. https://www.sciencedirect.com/science/article/pii/B9780128099650000331.
11. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4861670/.
12. https://www.newscientist.com/article/mg22329810–500-let-the-sunshine-in-we-need-vitamin-d-more-than-ever/.
13. http://journals.sagepub.com/doi/full/10.1177/1352458517738131.
14. https://www.ncbi.nlm.nih.gov/pubmed/29102433.
15. https://www.ncbi.nlm.nih.gov/pubmed/4139281/.
16. Scott Byrne, in discussion with the author.
17. https://www.omicsonline.org/open-access/uv-irradiation-of-skin-regulates-a-murine-model-of-multiple-sclerosis-2376–0389–1000144.php?aid=53832.
18. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5954316/.
19. Richard Weller, in discussion with the author.
20. In one study, Weller and his colleagues exposed people to 22 minutes of UVA light, and recorded a drop in diastolic blood pressure that was maintained for 30 minutes after the light was switched off: see https://www.ncbi.nlm.nih.gov/pubmed/24445737.
21. https://www.ncbi.nlm.nih.gov/pubmed/25342734.
22. https://www.ncbi.nlm.nih.gov/pubmed/26992108.
23. Even sun avoiders can get melanoma – possibly because of sunburn during childhood.
24. Another rich source of vitamin D is oily fish, which provides many other nutrients besides.
1. http://www.rug.nl/research/portal/files/3065971/c2.pdf.
2. From p. 5 of these excerpts: http://www.five-element.com/graphics/neijing.pdf.
3. Quoted in Russell Foster and Leon Kreitzman, Seasons of Life (Profile Books, London, 2009), p. 200–201.
4. Foster and Kreitzman, Seasons of Life.
5. According to the Diagnostic and Statistical Manual of Mental Health Disorders, Fifth Edition (DSM-5), which is widely used by psychiatrists, seasonal affective disorder is a subtype form of depression – major depressive disorder with a seasonal pattern. To receive a diagnosis, patients must therefore meet the diagnostic criteria for recurrent major depression or bipolar mood disorder – the difference is that their symptoms display a seasonal pattern; see https://bestpractice.bmj.com/topics/en-gb/985.
6. For a comprehensive history of seasonal affective disorder, I’d recommend C. Overy and E. M. Tansey, eds, The Recent History of Seasonal Affective Disorder (SAD), the transcript of a Witness Seminar held by the History of Modern Biomedicine Research Group, Queen Mary, University of London, on 10 December 2013; see http://www.histmodbiomed.org/sites/default/files/W51_LoRes.pdf.
7. https://jamanetwork.com/journals/jamapsychiatry/article-abstract/494864.
8. https://www.ncbi.nlm.nih.gov/pubmed/6581756.
9. https://www.ncbi.nlm.nih.gov/pubmed/2326393.
10. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4673349/.
11. https://www.arctic-council.org/index.php/en/about-us/member-states/norway.
12. https://www.ncbi.nlm.nih.gov/pubmed/8250679.
13. http://journals.sagepub.com/doi/10.1177/070674370204700205.
14. Overy and Tansey, eds, The Recent History of Seasonal Affective Disorder (SAD), 2013.
15. https://theconversation.com/a-small-norwegian-city-might-hold-the-answer-to-beating-the-winter-blues-51852.
16. Kari Leibowitz, in discussion with the author.
17. Overall, CBT and light therapy appear comparable in terms of reducing SAD symptoms, but certain symptoms (trouble falling asleep, excessive sleepiness, anxiety and social withdrawal) reduced more quickly in response to light therapy; see https://www.ncbi.nlm.nih.gov/pubmed/29659120.
18. https://www.ncbi.nlm.nih.gov/pubmed/26539881.
1. http://www.pbs.org/wgbh/nova/earth/krakauer-in-antarctica.html.
2. Foster and Kreitzman, Seasons of Life, p. 221.
3. They block the reuptake of serotonin, meaning that it sticks around in the junctions between neurons for longer, and therefore has more of an effect.
4. ‘Sex differences in light sensitivity impact on brightness perception, vigilant attention and sleep in humans’, S. L. Chellappa et al, in Scientific Reports 7, article no. 14215 (2017). Also ‘Influence of eye colours of Caucasians and Asians and the suppression of melatonin secretion by light’, S. Hrguchi et al, in American Journal of Physics – Regulatory, Integrative and Comparative Physiology, Vol. 292, issue 6.
5. Most studies that have investigated this have done so in the context of a hospital-like environment, where the lights often remain switched on 24/7, and noise can similarly disrupt sleep.
6. It is still not perfect: the light from current dawn simulation clocks is far dimmer than daylight, and such devices are usually positioned behind people’s heads, rather than in front of them, meaning that less light reaches their eyes.
7. Hot baths before bed have been found to boost NREM sleep by 15 to 20 per cent; see Walker, Why We Sleep, p. 279.
1. Her name has been changed to protect her identity.
2. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0033292.
3. https://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0021785/.
4. A recent study at the ICU at Central Manchester Foundation Trust found an average daytime illuminance of 159 lux, which is 10 to 1,000 times dimmer than daylight, while night-time illuminance averaged 10 lux – around fifty times brighter than moonlight. Overnight, there were also several bright pulses of light (measuring up to 300 lux), because of procedures or checks being carried out.
5. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4507165/.
6. http://journals.sagepub.com/doi/full/10.1177/1477153512455940.
7. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1296806/?page=2.
8. https://www.ncbi.nlm.nih.gov/pubmed/27733386.
9. https://www.thelancet.com/journals/lancet/article/PIIS0140–6736%2817%2932132–3/fulltext?elsca1=tlpr.
10. http://stm.sciencemag.org/content/9/415/eaa12774.
11. http://stm.sciencemag.org/content/9/415/eaa12774.
12. http://www.cochrane.org/CD006982/NEONATAL_cycled-light-intensive-care-unit-preterm-and-low-birth-weight-infants.
13. Data presented at the 2017 meeting of the Society for Light Therapy and Biological Rhythms in Berlin.
14. https://jamanetwork.com/journals/jama/fullarticle/273623.
15. http://www.pnas.org/content/111/45/16219.
16. https://www.ncbi.nlm.nih.gov/pubmed/4076288.
17. https://www.ncbi.nlm.nih.gov/pubmed/2179481.
18. https://www.ncbi.nlm.nih.gov/pubmed/22745214.
19. https://www.ncbi.nlm.nih.gov/pubmed/22745214.
20. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4874947/.
21. The full quote is: ‘It is often thought that medicine is the curative process. It is no such thing; medicine is the surgery of functions, as surgery proper is that of limbs and organs. Neither can do anything but remove obstructions; neither can cure; nature alone cures. Surgery removes the bullet out of the limb, which is an obstruction to cure, but nature heals the wound. So it is with medicine; the function of an organ becomes obstructed; medicine so far as we know, assists nature to remove the obstruction, but does nothing more. And what nursing has to do in either case, is to put the patient in the best condition for nature to act upon him.’ Florence Nightingale: The Nightingale School, Lynn McDonald, ed., Wilfrid Laurier University Press, Waterloo, Ontario, 2009, p. 683.
1. http://www.espn.co.uk/nba/story/_/id/17790282/the-nba-grueling-schedule-cause-loss.
2. Research presented at the Sleep 2017 meeting in Boston.
3. ‘The effects of sleep extension on the athletic performance of collegiate basketball players’, C. D. Mah et al, Sleep 2011; 34(7): 943–50.
4. Kevin Bickner, in an interview with Ben Cohen, Wall Street Journal, 7 February 2018.
1. Kantermann describes this in the TED talk he gave in Groningen 2016.
2. https://www.theatlantic.com/health/archive/2014/02/the-town-thats-building-life-around-sleep/283553/.
3. There’s less call for it in countries closer to the equator, where dawn and dusk are more uniform throughout the year.
4. For early-rising farmers, at some latitudes, DST robs them of morning daylight.
5. Winston Churchill, ‘A Silent Toast to William Willett’, Finest Hour (Journal of the International Churchill Society), 114, spring 2002.
6. https://www.bmj.com/content/1/2632/1386.
7. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4513265/.
8. http://psycnet.apa.org/record/2010–22968–001.
9. https://www.ncbi.nlm.nih.gov/pubmed/22369272.
10. https://www.bbc.co.uk/news/world-europe-45366390.
11. According to plans put forward in a Private Member’s Bill in 2010, the UK would still retain DST, so we would in effect have double summer time between late March and late October.
12. https://www.cell.com/current-biology/pdf/S0960–9822(06)02609–1.pdf.
13. Here, the difference seems to be 2 minutes per degree – although possibly the data is less accurate because the US population is so concentrated in urban areas – making the difference between an eastern state like Maine and a western one like Indiana – both of which are within the Eastern time zone – approximately 40 minutes. I wrote about this research in New Scientist: https://www.newscientist.com/article/2133761-late-nights-and-lie-ins-at-the-weekend-are-badfor-your-health/.
14. The original reason for the switch was a Russian Academy of Medical Sciences report, which stated that, when the clocks changed, there was a 1.5-fold increase in heart attacks, and that the rate of suicides grew by 66 per cent.
15. Social jet lag is defined as the difference between your midpoint of sleep on work (or school) days, and the midpoint on free days. Say you go to bed at 11 p.m. and wake at 7 a.m. on work days (mid-sleep at 3 a.m.) and go to bed at 2 a.m. and wake at 10 a.m. on weekends (mid-sleep at 6 a.m.), you would experience three hours of social jet lag per week.
16. https://www.sciencedirect.com/science/article/pii/S0960982212003259.
17. Teenagers need more sleep than adults, so it’s important to let them catch up on missed sleep rather than turfing them out of bed on a Saturday morning. It’s far better to encourage them to go to bed earlier all week-round, by maximising daylight exposure, and by minimising exposure to blue light in the evenings.
18. https://www.sciencedirect.com/science/article/pii/S0262407917317700.
19. https://www.ncbi.nlm.nih.gov/books/NBK222802/.
20. https://conservancy.umn.edu/bitstream/handle/11299/4221/CAREI%20SST-1998VI.pdf?sequence=1&isAllowed=y.
21. https://www.ncbi.nlm.nih.gov/pubmed/20603459.
22. http://pediatrics.aappublications.org/content/pediatrics/early/2014/08/19/peds.2014–1697.full.pdf.
23. https://www.frontiersin.org/articles/10.3389/fnhum.2017.00588/full.
24. Foster and Kreitzman, Circadian Rhythms, p. 15.
25. http://mikechristian.web.unc.edu/files/2016/11/Christian-Ellis-SD-AMJ-2011.pdf.
26. http://journals.sagepub.com/doi/abs/10.1177/0956797614541989?journalCode=pssa