New research suggests that exposure to outdoor artificial light at night increases the risk of diabetes

A new study published in Diabetology (Journal of the European Association for the Study of Diabetes [EASD]) has found that outdoor artificial light (LAN) at night is associated with impaired blood sugar control and an increased risk of diabetes, with more than 9 million cases of diabetes in China due to exposure to LAN
.
The study was done by Dr.
Yu Xu and colleagues from the Institute of Endocrine and Metabolic Diseases, Ruijin Hospital, Shanghai Jiao Tong University School of
Medicine.

Exposure to man-made local area networks at night is a pervasive environmental risk factor
in modern society.
The intensity of urban light pollution has increased to affect not only residents of large cities, but also those in remote areas that may be hundreds of kilometers away from the light source, such as suburbs and forest parks
.
"Although more than 80% of the world's population is exposed to light pollution at night, it is only in recent years that the issue has received limited attention
from scientists," the authors note.

The 24-hour circadian cycle on Earth has led to the fact that most living things, including mammals, have an intrinsic circadian (about 24 hours) timing system to accommodate nature's light-dark cycles
.
Light pollution has been found to alter circadian rhythms of insects, birds and other animals, leading to premature death and loss of biodiversity
.

By changing the timing of food intake, artificial LANs are also considered to be a potential cause
of metabolic disorders.
Rats exposed to artificial LAN developed glucose intolerance, manifested by elevated
blood glucose and insulin.
Another study found that mice exposed to weak white light at night for 4 weeks gained weight and had reduced glucose tolerance compared to animals in complete darkness at night, although their energy expenditure and expenditure were roughly comparable
.

There is also a link
between artificial local area networks and human health problems.
A study of night shift workers found that people exposed to brighter LANs were more likely to disrupt circadian rhythms and were
at greater risk of coronary heart disease.
Other studies have found that higher LAN exposure is associated with a 13% and 22% increase in the likelihood of being overweight and obese, respectively, while exposure to LAN in bedrooms has been reported to be positively associated
with the likelihood of diabetes in older adults.

The potential impact of outdoor artificial LANs was revealed in a South Indian study that used satellite imagery to map light pollution and compare
it to general health indicator data for adults in the region.
As the strength of the local area network increases, so do the average body mass index (BMI), systolic blood pressure, and "bad" (LDL) cholesterol levels of the exposed population
.

Diabetes is a serious public health problem in China, and the onset and progression of the disease is largely influenced
by behavioral and environmental risk factors.
The country's rapid urbanization and economic growth has led to a dramatic increase in urban lighting, as well as the number of
people exposed to it.
People living in cities easily transition from the natural 24-hour day-night cycle to 24-hour work and leisure, often staying outside late and exposing themselves to
artificial LANs.

The study used data from the China NCD Surveillance Study; This is a representative sample survey
of the general population conducted in 162 locations across the country in 2010.
A total of 98,658 adults participated in the survey, who were interviewed and collected information
such as demographics, medical care, household income, lifestyle, education and family history.
The average age of the participants was 42.
7 years, and about half of them were women
.

The participants' weight and height were measured to calculate BMI, and blood samples were taken to obtain fasting and postprandial (postprandial) blood glucose levels as well as glycated hemoglobin (HbA1c).

This is a type of glucose that binds to hemoglobin as a moving average
of blood glucose over the past 8 to 12 weeks.

Using nighttime low-light imagery data from the Earth's surface provided by the U.
S.
Defense Weather Satellite Program (DMSP), the researchers assigned participants at each study site an average level of artificial outdoor LAN exposure at that site
.
Exposure levels are divided into 5 quintiles from low to high (20% per group from high to low), with the median light intensity in the highest quintile being 69 times
that of the lowest quintile.

The intensity of outdoor LANs varies widely across China, with most areas exposed to low-intensity light, while high-intensity light is concentrated in eastern coastal cities
.
Participants living in the high quintile of outdoor LANs were more likely to be elderly, have a higher BMI and household income, and live in urban areas
.
In contrast, people living in a lower quintile reported higher levels of physical activity but shorter
years of schooling.

The study found a relative increase in diabetes prevalence of 28%
in the highest fifth of local-area network exposure compared to the lowest quintile.
Long-term exposure to residential outdoor LANs was positively correlated with blood glucose levels, insulin resistance, and diabetes prevalence, and negatively correlated with β cell function, even after adjusting for many important diabetes risk factors
.
On average, 1 more person in 42 people living in the highest fifth of areas with the highest LAN exposure will develop diabetes, and if these people live in the lowest quintile, they will not develop diabetes
.
While the association between LAN exposure and diabetes may not be as strong as the more well-known risk factors, the ubiquity of outdoor artificial light means that the size of the population exposed to it is huge
.

Researchers estimate that more than 9 million cases of diabetes in adults over the age of 18 in China can be attributed to outdoor LAN exposure; This number is expected to increase
as urbanization accelerates and more rural populations migrate from cities to cities.
The fact that an estimated 83 per cent of the world's population and more than 99 per cent of the population in the United States and Europe live under light-polluted skies illustrates the global nature and scale of
the problem.

These findings inform a growing body of evidence that LAN is harmful to health and that it may be a potential new risk factor
for diabetes.
The authors conclude that "further research, including direct measurement of an individual's exposure to LAN, is needed to determine whether it is causally related to diabetes"
.