Exposure to light at night-time increases women’s risk of breast cancer by up to 14% by disrupting a protective hormone
- The more outside light a woman is exposed to, the higher her risk of the disease
- Yet, these outcomes are only true for pre-menopausal women or ex-smokers
- Women who work night shifts are particularly susceptible to getting the disease
- Light at night reduces levels of the hormone melatonin, which disrupts sleep
- Melatonin has also been found to suppress the growth of breast cancer tumors
Exposure to light at night-time increases women's risk of breast cancer by up to 14 percent, new research reveals.
The more outside light that shines through a woman's bedroom window, the greater her risk of developing the disease, a study suggests.
Past research shows exposure to light at night decreases levels of the hormone melatonin, which can disrupt the internal 'clock' that regulates sleepiness.
Melatonin has also previously been found to suppress the growth of breast cancer tumors.
Lead author Professor Peter James from Harvard University, said: 'Our results suggest that this widespread exposure to outdoor lights during nighttime hours could represent a novel risk factor for breast cancer.'
Exposure to light at night increases women's risk of breast cancer by up to 14 percent (stock)
How the study was carried out
The researchers analyzed nearly 110,000 women enrolled in the Nurses' Health Study II between 1989 and 2013.
They linked satellite images taken at night-time to the address of each participant.
Whether the participants worked night shifts was also evaluated.
Outside light increases cancer risk by up to 14%
Results reveal women exposed to the highest levels of light at night are 14 percent more likely to develop breast cancer than those getting the lowest amount.
Breast cancer rates increase proportionally to the degree of outside light exposure.
Yet, for unclear reasons, these outcomes only occur in pre-menopausal women or ex-smokers.
All night shift workers are particularly at risk of developing the disease.
'In our modern industrialized society, artificial lighting is nearly ubiquitous'
Professor James said: 'In our modern industrialized society, artificial lighting is nearly ubiquitous.
'Our results suggest that this widespread exposure to outdoor lights during nighttime hours could represent a novel risk factor for breast cancer.'
Previous research suggests exposure to light at night-time decreases levels of the hormone melatonin, which can disrupt the internal 'clock' that regulates sleepiness.
Melatonin has also been found to suppress the growth of breast cancer tumors.
The findings were published in the journal Environmental Health Perspectives.
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