Turn off the lights?
American Heart Association
Bright,
outdoor lights are used at night to enhance the visibility of the environment,
improving human safety and comfort. However, the excessive use of artificial
light has resulted in about 80% of the world's population living in
light-polluted environments, according to the study's authors.
While
previous studies have linked increased exposure to bright, artificial light at
night to the development of cardiovascular disease, this is one of the first
studies to explore the relationship between exposure to light pollution at
night and the potential risk to brain health and stroke.
"Despite significant advances in reducing traditional cardiovascular risk factors such as smoking, obesity and Type 2 diabetes, it is important to consider environmental factors in our efforts to decrease the global burden of cardiovascular disease," said one of the corresponding authors Jian-Bing Wang, Ph.D., a researcher in the department of public health and department of endocrinology of the Children's Hospital, Zhejiang University School of Medicine and the National Clinical Research Center for Children's Health in Hangzhou, China.
In a review
of 28,302 adults living in China, exposure to residential outdoor nighttime
light was assessed by satellite images that mapped light pollution. Cases of
stroke were confirmed by hospital medical records and death certificates.
The analysis
of data including six years of follow-up with participants found:
·
1,278 people developed cerebrovascular
disease, including 777 ischemic (clot-caused) stroke cases and 133 hemorrhagic
(bleeding) stroke cases.
·
People with the highest levels of
exposure to outdoor light at night had a 43% increased risk of developing
cerebrovascular disease compared to those with the lowest levels of exposure.
·
People with the highest levels of
exposure to particulate matter 2.5 (PM2.5 is primarily
emissions from combustion of gasoline, oil, diesel fuel or wood) had a 41%
increased risk of developing cerebrovascular disease compared to participants
with the lowest levels of exposure to PM2.5.
·
Participants with the highest levels
of exposure to PM10 (PM10 is primarily from
dust and smoke) had a 50% increased risk of developing cerebrovascular disease
compared to those with the lowest exposure to PM10.
·
Participants with the highest exposure
to nitrogen oxide (emissions from cars, trucks and buses, power plants and
off-road equipment) had a 31% higher risk of developing cerebrovascular disease
compared to those with the lowest exposure.
Of note, an
additional analysis that included both outdoor light at night and pollution
found that the associations with increased risk of cerebrovascular disease
persisted, except for ischemic stroke.
"Our
study suggests that higher levels of exposure to outdoor artificial light at
night may be a risk factor for cerebrovascular disease," Wang said.
"Therefore, we advise people, especially those living in urban areas, to
consider reducing that exposure to protect themselves from its potential
harmful impact."
Artificial sources of light include fluorescent, incandescent and LED light sources. Continuous exposure to these light sources at night can suppress melatonin production, a hormone that promotes sleep. This can disrupt the 24-hour internal clock in people and impair sleep.
People with poor sleep, compared to
good sleepers, are more likely to experience worse cardiovascular health over
time, according to the study. The American Heart Association's Life's Essential
8 includes healthy sleep as one of the eight healthy lifestyle behaviors and
health measures that drive optimal cardiovascular health.
"We need
to develop more effective policies and prevention strategies to reduce the
burden of disease from environmental factors such as light as well as air
pollution, particularly for people living in the most densely populated,
polluted areas around the world," Wang said.
Study
background and details:
·
The analysis was conducted from 2015
to 2021 and included adults without cardiovascular disease who lived in Ningbo,
a major port and industrial city on China's east coast, with a population of
more than 8.2 million people according to the 2020 Chinese national census.
·
The average age of study participants
was 62 years and about 60% were women.
·
Participants were enrolled from
2015-2018 and followed for up to six years for cerebrovascular disease,
ischemic stroke and hemorrhagic stroke.
·
People with unavailable addresses or
error records, missing covariate data (data not included in the original study
that might alter outcomes), extreme levels of exposure to outdoor light at
night, previously diagnosed with cerebrovascular disease at enrollment and
within 1 year after enrollment were excluded from the analysis.
There were several limitations to the study, including that it did not obtain data on indoor lighting products and shading measures such as blackout curtains used by participants during nighttime.
Additionally, satellite-based products rarely capture blue light sources, which may lead to an underestimated association between outdoor light at night and cerebrovascular disease; and the population studied was from one city in China, therefore the findings may not apply to people in other communities with different exposure to outdoor light at night. Larger prospective studies are needed to confirm these findings.
