Cancer research: Bright outdoor lighting increases the risk of breast cancer in women

Is there a connection between nighttime outdoor lighting and breast cancer?
There are a number of environmental factors that affect the risk of developing breast cancer. Researchers have now found that in areas with an increased concentration of outdoor light at night, women have an increased risk of breast cancer, compared to women in areas with lower levels of outdoor light at night.

The scientists from the internationally recognized Harvard T.H. Chan School of Public Health found in their investigation that an increased concentration of outdoor lighting at night leads to an increased risk of breast cancer in women. This connection was even stronger when women worked the night shift. The doctors published the results of their study in the journal "Environmental Health Perspectives".

Outdoor lighting during the night Risk factor for the development of breast cancer
In our modern industrialized society, artificial lighting is almost over-present. The widespread exposure to outdoor lighting during the night could constitute a new risk factor for breast cancer, explains the author Professor Peter James from the Harvard Pilgrim Health Care Institute.

Nocturnal outdoor lighting influences our internal clock
Previously, the results of studies had suggested that exposure to light at night could result in a reduced level of the melatonin hormone. This effect can disrupt the so-called circadian rhythms, which are also referred to as our internal clock, the researchers say. Our internal clock affects our tiredness and general alertness, which in turn can lead to an increased risk of breast cancer.

Scientists analyze the data of almost 110,000 women for their study
The new study was the most comprehensive study to date on possible links between outdoor light at night and breast cancer, the authors say. To do this, the doctors looked at the data from almost 110,000 women who were part of the so-called Nurses ’Health Study II, which took place between 1989 and 2013.

Researchers use nocturnal satellite images of the participants' homes
For their investigation, the researchers linked the data with the recordings of satellite images of the earth, which were taken at night at the study participants' home addresses. The experts also examined the influence of shift work at night. The study also considered detailed information about a variety of health and socio-economic factors among participants, the authors explain.

Increased risk of breast cancer was around 14 percent in some women
The women who were exposed to the highest concentration of outside light at night were about 14 percent more likely to develop breast cancer during the period of the study compared to women in the lower fifth of exposure to nighttime outside light, say the authors in a press release from Harvard TH Chan School of Public Health. The results clearly show that if the concentration of outside light increases at night, the rates of breast cancer also increase, the scientists explain. (as)

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