Want better sleep? Get savvy with light.

Short sleep and sleep deprivation have been linked with a variety of mental deficits (including problems with decision-making and memory) and physiological changes too, including an increase in levels of inflammation in the body [1]. Inflammation in the body may contribute to impaired function of hormones such as insulin (insulin resistance) and leptin (leptin resistance) – both of which are implicated in obesity. In one study, just one night of about 4 hours sleep was enough to impair insulin functioning [2]. Short sleep has also been found to lower leptin levels [3] and increase cortisol levels [4] (excess cortisol can cause fat deposition, usually around the midriff).

Sleep deprivation may impair the rate at which we burn fat. In one study, disrupting men’s sleep with an alarm clock and allowing them only an average of 6½ hours of sleep, compared with no alarm clock and 8 hours of sleep, caused their fat metabolism to fall by two-thirds [5]. Perhaps not surprisingly, a lack of sleep can also lead to unhealthy changes in body composition. In one study, shortened sleep was found to reduce fat loss but increase muscle loss [6]. This effect may be related to sleep deprivation's ability to increase cortisol levels, as this hormone predisposes to muscle loss and fat gain.

Bearing all this in mind, it’s perhaps no great surprise that some researchers have suggested that changes in sleep patterns over recent decades might be an important but under-recognised factor in the burgeoning rates of obesity and chronic disease [7].

I don’t believe that all people who get a short amount of sleep are putting themselves at risk: I suspect there are people who generally thrive on short sleep. However, I also believe that, as a whole, many individuals are ‘pushing it a bit’, and simply are not getting the amount or quality of sleep required to be at their best or enjoy the best of health.

I sometimes ask people how many hours of sleep they feel they need to feel and function optimally. Then I ask them how many hours of sleep they get in the week. Almost invariably, the latter figure they give me is one hour less than the former.

There is now widespread recognition that our natural body clock may become disrupted by our exposure to light. In one study, a group of adults was monitored in their normal environments (with electric lighting, TV, and electronic devices), and their melatonin levels were also assessed [8].

It turned out that in their normal environment, melatonin secretion was generally delayed at night. Also, at 8 o’clock in the morning melatonin levels were still raised, and remained high for several hours after they got up. High levels of melatonin are good when we want to sleep, but not so good if we want to feel fully energised and ‘raring to go’.

This ‘delaying’ effect on melatonin is not too much of a surprise, as previous research has produced similar findings. In one study, exposure to room lighting before bedtime delayed melatonin secretion by an average of 90 minutes and reduced the overall amount of melatonin [9]. In another study, light from laptops and tablets was found to suppress melatonin as well [10].

The study subjects were then taken camping for a week, with the only light they were exposed to coming from the sun and a campfire. By the end of the week, the study subjects had their sleep ‘synchronise’ with the setting and rising of the sun. The sleep-wake cycle shifted by about 2 hours back (earlier). And in the morning, melatonin levels were found to be low (as they should be).

Getting more natural light during the day was likely a significant factor here, I think. Melatonin is actually made from the brain chemical serotonin, whose production is stimulated by sunlight.

It’s generally impractical for many of us to live ‘under canvas’, but there are steps we can take to give our brain the best chance of being ‘in sync’ with natural sleep cycles. There is some evidence that getting sunlight exposure within one or two hours of rising is particularly important, partly because it generally reduces melatonin quickly and helps ensure melatonin is secreted at the appropriate time and in appropriate amounts in the evening. The end result: more and better sleep.

Morning light tends to be rich in the blue part of the light spectrum – all good during the day. However, it’s also this type of light that can disrupt sleep. One solution might be to don a pair of blue-light-blocking (orange) sunglasses.

Orange-tinted lenses filter out blue light and, theoretically, should help sleep. In one study, wearing orange-tinted glasses for 3 hours before sleep improved both sleep quality and subsequent mood [11].

F.lux (justgetflux.com) is free software that takes blue light out of computer screens (both Windows and Mac) at dusk and restores it at dawn. Settings (such as Night Shift on iOS and Night Light on Windows) may also be useful.

In short, for the best sleep, we want plenty of natural light exposure during the day - particularly in the morning – but we want to limit light exposure in the evening. Optimising and limiting light at appropriate times can significantly enhance the quality and quantity of sleep we get, which can have a huge knock-on effect on our wellbeing and performance.

References:

1. Meier-Ewert HK, et al. Effect of sleep loss on C-reactive protein, an inflammatory marker of cardiovascular risk. J Am Coll Cardiol 2004;43(4):678-83

2. Donga E, et al. A single night of partial sleep deprivation induces insulin resistance in multiple metabolic pathways in healthy subjects. J Clin Endocrinol Metab. 2010;95(6):2963-8

3. Spiegel K, et al. Impact of sleep debt on physiological rhythms. Rev Neurol (Paris. 2003;159(11 Suppl):6S11-20

4. Reynolds AC, et al. Impact of five nights of sleep restriction on glucose metabolism, leptin and testosterone in young adult men. PLoS One 2012;7(7):e41218

5. Hursel R, et al. Effects of sleep fragmentation in healthy men on energy expenditure, substrate oxidation, physical activity, and exhaustion measured over 48 h in a respiratory chamber Am J Clin Nutr 2011;94(3):804-8

6. Nedeltcheva AV, et al. Insufficient Sleep Undermines Dietary Efforts to Reduce Adiposity. Ann Intern Med. 2010;153(7):435-41

7. Van Cauter E, et al. Metabolic consequences of sleep and sleep loss. Sleep Med 2008;9 Suppl 1:S23-8

8. Wright KP, et al. Entrainment of the Human Circadian Clock to the Natural Light-Dark Cycle Current Biology, 01 August 2013

9. Gooley JJ, et al. Exposure to room light prior to bedtime suppresses melatonin onset and shortens melatonin duration in humans. J Clin Endocrinol Metab 2011;96(3):E463-72

10. Wood B, et al. Light levels and duration determines the impact of self-luminous tablets on melatonin suppression. Applied Ergonomics 2013;44(2):237-240

11. Burkhart K, et al. Amber lenses to block blue light and improve sleep: a randomized trial. Chronobiol Int 2009;26(8):1602-12