Light – a doubled-edged sword for sleep

There have been reports in the UK press this week of a report that informs us that we are sleeping quite a lot less than we did a few decades ago, and the problems that may befall us as a result. Here’s a typical story which appeared in the UK broadsheet The Daily Telegraph.

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 participate in the poor functioning 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 also has been found to lower levels of the hormone leptin [3] and increased levels of the stress hormone cortisol [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 6½ hours sleep, compared to no alarm clock and 8 hours sleep, caused their metabolism of fat of to fall by two-thirds [5]. Perhaps not surprisingly, lack of sleep can also bring about unhealthy changes in body composition. In one study, shortened sleep was found to reduce fat loss but increase muscle loss [6]. This effect may have something to do with the ability of sleep deprivation to increase levels of cortisol, as this hormone predisposes to muscle loss as well as fat gain.

Bearing all this in mind, it’s perhaps no great surprise that some researchers have suggested changing 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 tend to get short amount of sleep are putting themselves at risk: I suspect there exists 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 of hours of sleep they get in the week. Almost invariably, the latter figure they give me is one hour less than the former.

One thing that has been highlighted (excuse the pun) in the recent reports is sleep is how our natural body clock may become disrupted by an ever-lengthening day, as well as our exposure to light. It reminded me of a piece of research in which a group of adults were monitored in their normal environments (with electrical lighting, TV and electronic devices), and also had their levels of the ‘sleep hormone’ melatonin 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 prior to bedtime delayed melatonin secretion by 90 minutes on average, and reduced the overall amount of melatonin too [9]. In another study, light from laptops and tablet devices was found to suppress melatonin too [10].

The study subjects were then taking 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 is very likely to have been a significant factor here, I think. Melatonin is actually made from the brain chemical serotonin, the production of which 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. Two very simple things that might help is to be mindful of getting exposure to natural sunlight each day, and to think about importance of keeping light exposure to a minimum in the evening.

It’s the blue part of the visual spectrum that appears to be most beneficial during the day, but also is the most disruptive at night. 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, the use of orange-tinted glasses 3 hours prior to sleep improved both the quality of sleep and subsequent mood [11].


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






14 Responses to Light – a doubled-edged sword for sleep

  1. Moy Peralta 16 May 2014 at 8:04 am #

    Ah, Dr. Briffa! I would’ve preferred you to have immediately commented on yesterday’s ramped-up government propaganda for the safety of statins… and Rory Collins’ input.

  2. Susan Wallace 16 May 2014 at 1:05 pm #

    Very interesting article, Dr B.

    Another solution when using a computer in the evening could be to download something like “f.lux” (F.LUX) which adapts the colour of your computer’s display according to the time of day.

    In the evening, the light from your screen is more on the orange spectrum, filtering out the blue light. But during the day, the light returns to the “daylight” setting.

    The filter can be turned off whenever you don’t want it, and you can set the timings to suit your own requirements.

    • Pingo 17 May 2014 at 12:19 pm #

      Susan, I have had f.lux on my computer since end of last year and it works as it should. However my latitude is close to the artic circle and the program doesn’t allow such high latitudes so I have to settle for 65 degrees north and that is close enough.

  3. RachaelM 16 May 2014 at 9:56 pm #

    Would be interesting to know sleep’s effect on weight gain and muscle loss in patients (I do acupuncture) who work night shifts with irregular work/sleep cycles, that is differing nights on and nights off, not regular set schedule. Have a number of male patients working for the airlines as mechanics, now in their late 50’s/early 60’s who have worked their shifts for decades. All have metabolic disturbances with weight gain and muscle strength issues, and many problems due to irregular sleep cycles. They don’t have the luxury to change shifts or jobs.

  4. Chris 18 May 2014 at 3:22 pm #

    A most excellent review Dr Briffa, one that illuminates that our body ought to be attuned to natural cycles or light and dark, and how lifestyles have drifted out of sync with with natural cycles due to possibilities greatly promoted by the invention of the electric light bulb. And it is not just daily cycles that bear upon our hormones, but also seasonal variations in the length of day, whose significance is increased at greater latitudes.

    Wiley and Formby wrote a highly credible book on the subject (Lights Out) and since reading that there is much about diet, lifestyle, and environmental matters that became much clearer. As I result I became more respectful for the involvement of hormones in peoples actions and behaviour and figured that wellness ought to accompany a history of hormones describing normal balances and following normal rhythms. Illness, chronic illness, is something we ought to expect to follow chronic hormonal imbalances and aberrant cycles.

    After reading ‘Lights Out’ I try to sleep for at least nine hours if I can, but certainly I am mindful that sufficient sleep, preferably taken when it;s dark outdoors, and in a room which is adequately dark, is one route to help establish a datum from which healthy hormonal levels, balances, and rhythms ought to follow. On a work-day (really night) I cannot retire until around 6am. I’ve had blackout lining with curtains for years, but lately I’ve doubled-up and have a blackout roller-blind over the window too. Then as if that isn’t quite enough I do detect an eye-mask cuts out even more light, making for better sleep, longer sleep, a more balanced and rested feeling on awakening, and fewer yawns over the course of my working ‘day’.

    Coming to an appreciation of benefits is relatively easy if approached from the natural angle, but being a newcomer to interest in hormones and physiology brings its frustrations. To mention increased levels of cortisol and increased measures of inflammation invites repost since it is said cortisol is a powerful ant-inflammatory. Paradoxically chronic hypercortisolemia is mooted to associate with raised levels of homocysteine; with homocysteine being recognised as a highly reactive oxidising agent capable of conveying oxidative stress and promoting the advance to the kinds of chronic illnesses in which inflammation is regularly suggested to be a factor too. My present working understanding is that raised levels or cortisol raise demands upon methyl donating antioxidants and it is scarcity of of methyl donors, ralative to demand, that might then result in basal levels of oxidative stress trending higher. Higher homocysteine detected by tests might indicate demand for B6, B12, and folic acid has consistently exceeded supply. Hence the consequence of chronically disturbed levels of cortisol may run counter to the impression stemming from one of of its claimed primary functions. Endocrinology is mind-field, potentially.

  5. Mary 20 May 2014 at 4:12 pm #

    The need for so many in the US to hold down two jobs and the belief that ‘busy’ is virtue just adds to the problem.

  6. Christoph Dollis 20 May 2014 at 7:45 pm #

    This is an extremely important and accurate post. However, there is another factor that entrains the circadian rhythm even more powerfully than light and that is food. Specifically, meal timing.

    Earlier in the day is better. Lots of Paleo people advise skipping breakfast and eating later. However, for sleep anyway (and for weight loss) (and cortisol reduction) this is precisely backwards.

    Primates naturally gather food and eat during light, not dark. We go to ground at night (probably as an adaption for safety from adaptation as well as to regenerate our neural transmitters for our large and complex brains and to sift through memories, keeping the more useful ones). Until light made the opposite feasible, but our cirdadian rhythms and hormones then get out of whack.

  7. Paul 22 May 2014 at 8:59 am #

    Hi do you think any of the melatonin supplements work to help with sleep especially the sprays
    and thank you for a great article.

    • Christoph Dollis 23 May 2014 at 1:44 am #

      One thing I will say is that shifting your evening light-intake from blue light to red light (the glasses) allows your body to make more melatonin naturally.

  8. Diana Jeuda 27 June 2014 at 7:28 pm #

    Does when you sleep matter, provided you get say 6 hours?

    As I’ve got older, I’ve found I’ve wakened at 2 or 3 in the morning and have found it difficult to get back to sleep for a couple of hours or more.

    As I’m retired, sometimes I can sleep in to compensate for this, but this is not always possible. As a result I’ve taken to napping to compensate if I’m feeling tired in the late afternoon. It doesn’t seem to make any difference to my sleep patterns whether I nap or not.

    I’m healthy, not overweight and take regular exercise.


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