We who live in developed countries live in a world of artificial lights which light up our world at any time of the day. Isn’t it convenient to have light at the push of a button, at the flick of a switch?
But the use of artificial lights seems to have its drawbacks. Exposure to artificial light at night may actually promote cancer.
In a study more than 2 years ago, researchers from the Stony Brook University found a link between the use of night lights and breast cancer incidence in more than 1000 women. Among women who woke up frequently during the night and turn on the lights, the association was 65%. For those who are habitually awake at night such as shift workers, the association is less at 45%.
A more recent study was conducted by researchers at the University of Haifa. The research looked at the influence of environmental factors – including artificial light exposure – on the incidence of prostate, lung, and large intestine in cancer in men from different populations all over the world. Data was collected from a database of the International Agency for Research on Cancer (IARC), on the incidence of these types of cancer in men in 164 countries.
The results of the study showed that there is a link between levels of artificial night illumination and incidence of prostate cancer.
Data on night time illumination were collected from satellite images of the Defense Meteorological Satellite Program (DMSP) and were adjusted by the geographic distribution of the population of a certain country. The researchers came up with an objective measurement of night light exposure in terms of “the amount of artificial light per night per person.”
Based on the illumination data, countries could be classified into three categories, namely:
- little exposure to lighting at night
- medium exposure
- high exposure
Prostate cancer incidence in countries with low exposure is 66.77 per 100,000 inhabitants. This increased by 30% to 87.11 per 100,000 inhabitants in medium exposure countries. In countries with the highest level of exposure to artificial light at night, the incidence was 157 per 100,000 inhabitants – an increase of 80%.
So how does night time illumination promote cancer? Several hypotheses have been put forward but the most likely explanation is due to the hormone melatonin. At night, the hormone melatonin streams into the bloodstreams and flows throughout the night, suppressing cancer cells. Melatonin is switched off — and estrogen switches on — by the presence of light.
With the suppression of melatonin production, the immune system is also suppressed and the circadian rhythm is disrupted, causing confusion between night and day.
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