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Higher levels of exposure to outdoor artificial light at night are significantly linked with markers of diabetes and impaired glucose homeostasis, in a new national, cross-sectional study from China.

The results showed a 7% significant increase in diabetes prevalence per quintile exposure to artificial light at night (prevalence ratio [PR], cialis web page 1.07), report Ruizhi Zheng, PhD, of the Shanghai Jiaotong University School of Medicine in China, and colleagues. People living in areas with the most exposure to light at night had a 28% higher prevalence of diabetes than those living in places with the lowest exposure (PR, 1.28), the researchers found.

The study was published online November 14 in Diabetologia.

Previous animal studies have shown that exposure to light at night may interfere with circadian rhythms and affect glucose homeostasis, the study team note. Other research has demonstrated that chronic exposure to moderate indoor light during sleep elevated the prevalence of diabetes in older adults compared to those sleeping in a dim setting, the authors add.

“Our findings contribute to the growing literature suggesting that artificial light at night is detrimental to health and demonstrate that artificial light at night may be a potential novel risk factor for diabetes,” they write.

“Considering the coexistence of the diabetes epidemic and the widespread influence of light pollution at night, the positive associations indicate an urgent need for countries and governments to develop effective prevention and intervention policies, and to protect people from the adverse health effects of light pollution at night,” the study authors stress.

Gareth Nye, PhD, senior lecturer at the University of Chester, UK, agreed that prior research has found an association between metabolic conditions, such as diabetes, and artificial light at night, with most theories as to the cause focusing on the body’s natural circadian cycle.

He said that internal clocks regulate a variety of bodily processes, such as metabolism and hormone synthesis. They also affect sleep patterns by interfering with synthesis of the hormone melatonin, which is essential for sound sleep, Nye told the UK Science Media Centre.

However, he stressed that much more research is needed before any link can be considered definitive.

Outdoor Night Light Exposure Linked to Fasting Glucose, A1c

The Chinese researchers set out to approximate the relationships between diabetes prevalence and glucose homeostasis with chronic exposure to outdoor light at night. 

They assessed 98,658 participants from the China Noncommunicable Disease Surveillance Study across 162 sites. The mean age of participants was 42.7 years. Females comprised 49.2% of the study cohort.

Diabetes was defined based on American Diabetes Association criteria. Satellite data were used to determine exposure to outdoor light at night in 2010. The associations between light exposure at night and indicators of glucose homeostasis were investigated.

Prevalence ratios were calculated and adjusted for sex, age, smoking status, education, body mass index, physical activity, household income, family history of diabetes, rural/urban areas, drinking status, and use of lipid-lowering prescription drugs (primarily statins) or antihypertensives.

The findings showed exposure levels to outdoor light at night were positively linked with 2-hour and fasting glucose concentrations, A1c, and insulin resistance (measured using homeostatic model assessment [HOMA]), but negatively related to β-cell function (measured using HOMA).

More Research Needed

“We advise caution against causal interpretation of the findings and call for further studies involving direct measurement of individual exposure to light at night,” the researchers conclude.

Nye agreed.

“One issue with this study is that the areas with the highest outdoor artificial light levels are likely to be those in urban areas and bigger cities. It has been known for a long time now that living in an urbanized area increases your risk of obesity through increased access to high-fat and convenience food, less physical activity levels due to transport links, and less social activities. The authors also state this, and the fact participants tended to be older,” he noted.

Large datasets are used in this investigation, however, which generally increases the reliability of the data, he observed.

But it is also “unclear as to whether the population here was selected for this study or was retrospectively analyzed, which poses reliability issues, as does the selection of the representative sample as it is not discussed,” he noted.

Ultimately, there is no confirmed evidence of the link, and until further work is done to directly link light exposure and diabetes in humans, “the link will remain an association only,” he concluded.

Diabetologia. Published online November 14, 2022. Abstract

Ashley Lyles is an award-winning medical journalist. She is a graduate of New York University‘s Science, Health, and Environmental Reporting Program. Previously, she studied professional writing at Michigan State University. Her work has taken her to Honduras, Cambodia, France, and Ghana, and has appeared in outlets such as The New York Times Daily 360, PBS NewsHour, The Huffington Post, Undark, The Root, Psychology Today, Insider, and Tonic (Health by Vice), among other publications.

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