RSSElectric light may cause cancer

Posted on Sun, 11 Oct 09

Electric light may cause cancer

“Night is no longer dark in the modern world, and the Milky Way has disappeared. Electric light has benefits but there are also a few detriments. These are [1] loss of the night sky, [2] wasted energy, [3] harm to animal and plant life, [4] and perhaps increases in some severe human maladies such as cancers of breast and prostate.” These are the words of Professor Richard Stevens, Cancer Epidemiologist. In the 1970s Stevens began to question why cancer rates dramatically rise as societies industrialise, a series of clues around this time led him to the propose the theory in 1987 that electric lighting at night disrupts natural human circadian rhythms causing changes in hormones that may be linked to breast cancer risk (1-2). The theory that light at night is linked to breast cancer, and perhaps others, is now well supported by evidence.

A clock out of time

Our body clock, better known as our circadian rhythm, is subject to a 24 hour cycle and governs daily changes our hormones, metabolism, alertness and body temperature.  If you have ever experienced jet lag you will known what disruption to this natural rhythm feels like. This 24 hour cycle is an ancient legacy from our ancestors who lived by cycles of day and night. In the modern world however the night is illuminated with electric lighting and as a consequence most people suffer a disrupted rhythm not only from exposure to artificial light during the night but also lack of exposure to natural sunlight in the morning (3). 

Restoring your rhythm

Accumulating evidence suggests that disruption to our circadian rhythm changes the timing of our biological clock and causes disruption in the balance of hormones which may then lead to cancer development. Central to this disruption are low levels of the hormone melatonin which is produced in response to darkness and known to suppress cancer development. Low melatonin levels also lead to high levels of hormone oestrogen, a key player in cancer development particularly of the breast and prostate (4).

As a solution Professor Stevens suggests industry rethink the design of our environment to better encourage natural circadian rhythms. However for now he suggests that the best solution it seems is to pay attention to the laws of the natural world, by getting an early night and taking an early morning walk in the sun (3-4).


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

2. Stevens RG, Electric power use and breast cancer: a hypothesis, Am. J. Epidemiol. 125 (1987) 556–561.

3. Stevens RG. Light-at-night, circadian disruption and breast cancer: assessment of existing evidence. Mutat Res. 2009 Sep-Oct;679(1-2):6-8.

4. Stevens RG. Artificial lighting in the industrialized world: circadian disruption and breast cancer. Cancer Causes Control. 2006 May;17(4):501-7.

Tags: Light At Night, Electric Lighting, Cancer, Breast Cancer, Melatonin

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