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exposure to outdoor lighting at nighttime may be a risk factor for breast
cancer development, a new study suggests.
Share on PinterestResearchers
suggest that nighttime exposure to outdoor light may raise the risk of breast
cancer for some women.
From
an analysis of almost 110,000 women, researchers found that those who resided
in areas with high levels of outdoor light at nighttime were more likely to
develop breast cancer compared with women who lived in areas with
low levels of outdoor light during the night.
Lead
study author Peter James, of the Harvard Pilgrim Health Care Institute at
Harvard Medical School in Boson, MA, and colleagues published their findings today in the journal Environmental Health Perspectives.
After skin cancer,
breast cancer is the most common cancer among women in
the United States. This year, it is estimated that around 252,710 new cases of invasive breast
cancer will be diagnosed in the U.S.
Risk
factors for breast cancer include inherited gene mutations, alcohol
consumption, overweight or obesity, and lack of
exercise. Increasingly, research has suggested that nighttime light exposure
may also play a role in breast cancer risk.
StudiesTrusted Source have associated exposure to
artificial light at night with a reduction in melatonin, which is the hormone
that regulates our sleep-wake cycles.
Darkness
triggers an increase in melatonin, which tells us when it is time to sleep. As
such, when we are exposed to artificial light at night, melatonin levels
decrease. This can cause sleep problems, which previous research has linked to increased
breast cancer risk.
Breast cancer risk increased by 14 percent
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For
the new study, James and his team sought to further explore the link between
nighttime light exposure and breast cancer risk. To do so, the researchers
analyzed the data of almost 110,000 women, all of whom participated in the
Nurses' Health Study II between 1989 and 2013.
Using
data from satellite images, the team assessed the levels of outdoor light at
night in the areas each woman resided. Data were also gathered on the women's
health, participation in night shift work, and socioeconomic factors.
Overall, compared with women who lived in areas with
the lowest levels of outdoor light at night, those who resided in areas with
the highest levels were found to have a 14 percent greater risk of breast
cancer.
What is more, the team
found that as levels of outdoor light at nighttime increased, so did the risk
of breast cancer.
Night shift workers at greatest risk
On
further investigation, the researchers found that the increased risk of breast
cancer with high levels of outdoor light exposure was only valid for
premenopausal women and women who were former or current smokers.
Additionally, this association was found to be
strongest for women who worked night shifts. The researchers speculate that
this is down to their greater exposure to artificial light at nighttime and the
disruption of their sleep-wake cycles.
While
further research is needed to confirm these results and the possible mechanisms
behind them, James and colleagues believe that their study may have identified
another potential risk factor for one of the most common cancers among women.
"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."
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