From the Journals

Night lights in the city link to increased risk of diabetes


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, 1.07), report Ruizhi Zheng, PhD, of the Shanghai (China) Jiaotong University School of Medicine, 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 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 with 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, England, 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, Dr. 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. Female participants 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).


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