Electric lighting, circadian disruption and disease: shedding light on a dark issue

Posted on Mon, 23 Jan 12

Increasing use of electric lighting has resulted in disruption of our circadian rhythm and, through subsequent changes in our metabolism may contribute to diseases as diverse as obesity and breast cancer. Ironically, this idea has largely remained in the dark.

Endless day

When you open your eyes in the morning light floods in and sets off an electrical impulse which runs down your optic nerve into a conveniently close part of your brain called the suprachiasmatic nuclei (SCN), also known as the master pacemaker. The SCN is your biological clock and synchronises all the cells in your body and their metabolic functions with the time of day (1).

Our synchronicity with light and dark cycles is one of our most ancient environmental relationships however we have broken our ties with nature’s natural light-dark rhythm. As Professor Richard G. Stevens, pioneer of the breast cancer and light at night theory, eloquently puts it:

“We, life on the planet, have evolved for several billion years with a reliable cycle of bright broadspectrum light (the Sun) and dark. This fundamental aspect of the environment has, not surprisingly, had a profound impact on the organization of our metabolic, cellular, and organismal processes. Suddenly (in evolutionary time), the bulk of humanity began to be exposed to light during the night after the introduction of electric power, and to dim, spectrum-restricted light during the day inside buildings. Everything changed, and not all for the good (2).”

While diet, exercise, smoking, and stress all receive a great deal of attention as environmental causes of disease few people consider light at night. Interestingly it was a dismay in a lack of a robust relationship between diet and breast cancer that lead the aforementioned Professor Stevens to first consider light at night as a risk factor. Even today the relationship between diet and breast cancer remains weak, light at night however is emerging as a strong risk factor and may well contribute to other common diseases (2).

What happens when you turn on the lights?

Although a poorly investigated area, experimental, epidemiological and some indirect evidence suggests that light at night may contribute to:

• Breast cancer risk (3)

• Prostate cancer risk (4)

• Attention deficit disorder (5)

• Night time eating syndrome (7)

• Diabetes, obesity and heart disease (8)

• Depression (9)

• Endometriosis (10)

• Colorectal cancer risk (11)

How your biological clock ticks

There are several proposed mechanisms for the link between light at night and disease including interaction with clock genes, circadian disruption of hormones such oestrogen, cortisol and insulin and behavioural changes. However one of the better understood pathways is disruption of the hormone melatonin. 

When you are exposed to complete darkness your pineal gland produces melatonin which could be viewed as the “arm of your biological clock” as it regulates your metabolism with day and night cycles (12). Conversely, when your eyes, or more specifically retina, are exposed to light melatonin production is suppressed (13). Beyond regulation of circadian rhythm melatonin is involved in blood pressure regulation, cancer prevention, reproductive health, immune function, and is a potent antioxidant (14).

Reset your rhythm 

The science has a way to go before we can confidently link light at night to disease (with perhaps the exception of breast cancer risk) however if you want to reset your biological clock here are a few considerations:

Test salivary melatonin: it is a non-invasive and accurate way to objectively assess whether or not you have a disrupted circadian rhythm (12). Even small changes in evening light exposure can affect melatonin concentrations (15).

Don’t take melatonin: unless you need it, don’t take supplemental melatonin. There is evidence that it could disrupt circadian rhythm in otherwise healthy people (16).

Spend more time in the dark: Professor Stevens recommends “extending the dark period at night to 9 or 10 hours if possible” which is perhaps be the best and safest way to get back in sync and maximise your melatonin production (16). 

Blackout the bedroom: if you, like many people, live in a heavily light polluted urban environment make sure you blackout your bedroom with some good blinds.

Books, not tablets: increasing use of electronic devices such as smart phones, tablets, e-readers and laptops is changing the way we are exposed to evening light (i.e. holding electrically lit screens in front of our eyes). Consider minimising exposure to these devices in the evening. 

Practice quite wakefulness:  many people do not realise that it is actually quite normal to wake during the night. It is. But if you do it’s best not to turn the lights on (16).

Red light your bathroom: the typical bathroom light is enough to suppress melatonin production so switch to red low-wattage light bulbs as they will minimise melatonin suppression (16).

Catch the sunrise: exposing your eyes to bright early morning light helps restore melatonin levels, a strategy that has been shown to be effective for reducing the effects of jet lag (17). If the sun is not available, try a dawn simulating light.

Wear amber glasses at night: sport a pair of amber glasses, preferably in the hours before bed, as amber glass blocks blue light wavelengths, the type of light that suppresses melatonin production during daylight hours (18).

Cereal for dinner: almost all plant foods including vegetables, fruits, and especially grains such as rice, corn and oats contain plant melatonin (phytomelatonin) (19). However it is not yet known whether phytomelatonin is actually absorbed from plants after we eat them so porridge for dinner is a long shot.

References:

1. Reiter R, et al.   Circadian mechanisms in the regulation of melatonin synthesis: disruption with light at night and the pathophysiological consequences.  J Exp Integr Med 2011; 1:13-22

2. Stevens RG. Electric light causes cancer? Surely you're joking, Mr. Stevens. Mutat Res. 2009 Jul-Aug;682(1):1-6.

3. Stevens RG. Working against our endogenous circadian clock: Breast cancer and electric lighting in the modern world. Mutat Res. 2009 Nov-Dec;680(1-2):106-8.

4. Kubo T, Ozasa K, Mikami E, et al. Prospective cohort study of the risk of prostate cancer among rotating-shift workers: findings from the Japan collaborative cohort study. Am J Epidemiol 2006; 164:549-55.

5. Weiss MD, Wasdell MB, Bomben MM, Rea KJ, Freeman RD. Sleep hygiene and melatonin treatment for children and adolescents with ADHD and initial insomnia. J Am Acad Child Adolesc Psychiatry 2006; 45; 512-9.

7. Qin LQ, Li J, Wang Y, Wang J, Xu JY, Kaneko T. The effects of nocturnal life on endocrine circadian patterns in healthy adults. Life Sci. 2003 Sep 26;73(19):2467-75.

8. Rüger M, Scheer FA. Effects of circadian disruption on the cardiometabolic system. Rev Endocr Metab Disord. 2009 Dec;10(4):245-60.

9. Boyce P, Barriball E. Circadian rhythms and depression. Aust Fam Physician. 2010 May;39(5):307-1

10. Marino JL, Holt VL, Chen C, Davis S. Shift work, hCLOCK T3111C polymorphism, and endometriosis risk Epidemiology 2008;19:477–84.

11. Schernhammer ES, Laden F, Speizer FE et al. Night-shift work and risk of colorectal cancer in the nurses’ health study. J Natl Cancer Inst 2003;95:825–28.

12. Mirick DK, Davis S. Melatonin as a biomarker of circadian dysregulation. Cancer Epidemiol Biomarkers Prev. 2008 Dec;17(12):3306-13.

13. Lewy AJ, Wehr TA, Goodwin FK, Newsome DA, Markey SP. Light suppresses melatonin secretion in humans. Science 1980;210:1267–69.

14. Altun A, Ugur-Altun B. Melatonin: therapeutic and clinical utilization. Int J  Clin Pract. 2007 May;61(5):835-45.

15. Zeitzer JM, Dijk DJ, Kronauer R, et al. Sensitivity of the human circadian pacemaker to nocturnal light: melatonin phase resetting and suppression. J Physiol 2000;526 Pt 3:695 – 702.

16. Stevens RG. Light-at-night, circadian disruption and breast cancer: assessment of existing evidence. Int J Epidemiol. 2009 Aug;38(4):963-70.

17. Burgess HJ, Crowley SJ, Gazda CJ, Fogg LF, Eastman CI. Preflight adjustment to eastward travel: 3 days of advancing sleep with and without morning bright light. J Biol Rhythms. 2003 Aug;18(4):318-28.

18. Alpert M, Carome E, Kubulins V, Hansler R. Nighttime use of special spectacles or light bulbs that block blue light may reduce the risk of cancer. Med Hypotheses. 2009 Sep;73(3):324-5.

19. Reiter RJ, Tan DX, Manchester LC, Simopoulos AP, Maldonado MD, Flores LJ, Terron MP. Melatonin in edible plants (phytomelatonin): Identification, concentrations, bioavailability and proposed functions. World Rev Nutr Diet. 2007;97:211-30.