Sleeping with lights on increases the risk of prostate cancer
Men who sleep in a dark bedroom are less likely to have prostate cancer than men who sleep with the lights on. Spanish researchers at the Barcelona Institute for Global Health report this in Environmental Health Perspectives.
Between 2013-2018, the researchers recruited 359 men aged 20-85 who had been diagnosed with prostate cancer by doctors. The men did not work in shifts.
By using questionnaires, the researchers determined the lifestyle of the men. The researchers also asked the men about their sleeping habits, and whether they slept at night in a dark or lit room.
In addition, the researchers studied 544 comparable men without prostate cancer.
Men who slept at night in a dark or dim bedroom were less likely to have prostate cancer than men who slept in an illuminated bedroom.
The researchers also determined the men's chronotype - i.e. whether they were morning or evening people. When the researchers then looked again at the effect of light in the bedroom, sleeping with an illuminated bedroom seemed to increase the risk of prostate cancer, especially in the morning people.
This trend was not statistically significant. But still.
One theory that perhaps explains the connection is that evening light suppresses the production of melatonin. Melatonin has an anti-estrogenic and anti-cancer effect.
"Findings from this large case-control study [...] provide some support for the influence of artificial light-at-night on the development of cancer in the general population", summarize the researchers.
"Men who reported the highest level of exposure to indoor artificial light-at-night were at greater risk of prostate cancer than men who reported no indoor illumination at night."
"In further studies it will be interesting to measure indoor light levels rather than using only questionnaire-based methodology, which is more subjective although it may capture a longer time span of exposure."
Environ Health Perspect. 2018 Apr 23;126(4):047011.
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