Artificial light at night might be the cause of diabetes in more than 9 million Chinese adults

According to a new study, exposure to outdoor artificial light at night (LAN) is associated with an increased risk of diabetes, along with impaired glucose control.

Artificial outdoor LAN exposure

Researchers have discovered that exposure to artificial light at night can be a risk factor for diabetes, with more than nine million cases of the disease in Chinese adults attributed to LAN. Diabetes is a critical public health concern for people in China, and globally.

The onset and progression of the disease is governed by behavioral and environmental risk factors, with artificial LAN being one of those environmental causes. The nation’s fast growth, development and economic progression has resulted in a dramatic increase in artificial LAN, and people exposed to it.

The study was led by Dr Yu Xu and her colleagues at the Shanghai Institute of Endocrine and Metabolic Diseases, Ruijin Hospital, Shanghai Jiaotong University School of Medicine in Shanghai, China.

The research from the study was published in Diabetologia (the journal of the European Association for the Study of Diabetes [EASD]).

The intensity of urban light pollution has increased drastically in both big cities and the suburbs, and even forest parks that are far away from light sources. This light is known to throw off the circadian timing center, or the body’s internal timekeeping process. The system, also known as the biological clock, is adapted to natural sequences within 24 hours of night and day. Light pollution has been known to kill insects, birds, and other animals by altering their circadian rhythm.

LAN and its effects on animals

Artificial light at night has also been linked to potentially causing metabolic dysregulation, or alterations within the body, by changing the timing of food intake. One study showed that rats exposed to artificial LAN developed variations in their systems that caused glucose intolerance, revealing higher blood sugar and insulin.

Another study found that mice exposed to nocturnal dim white light of minimum brightness for four weeks had increased body mass (BMI) and reduced glucose tolerance compared to the mice who had an environment that was completely dark at night with no artificial light.

Health effects of artificial outdoor LAN on humans

Researchers have found a correlation between artificial LAN and health problems in humans. A study of night shift workers found that those exposed to brighter artificial light at night were more likely to have interruptions in their circadian rhythms, along with a higher risk of coronary heart disease.

Another research study found that higher LAN exposure is associated with a 13% chance of being overweight and a 22% increase in the possibility of being obese. Exposure to artificial LAN in the bedroom has been found to affect elderly people, causing a probability of developing diabetes.

Initial study of artificial LAN

A preliminary study that examined the prospective impact of outdoor artificial LAN was done in South India. Researchers used satellite images to map light pollution and compare the information with health markers amongst adults in the area. The research team discovered that there were corresponding rises in body mass index, systolic blood pressure, and ‘bad’ cholesterol (LDL) levels in the population exposed to the light at night.

The artificial LAN research in China

The study used information from the China Noncommunicable Disease Surveillance Study. The research sampled a portion of the population in China taken in 2010 from over 160 sites across the country. In total, 98,658 adults participated in the study. The average age of the participants was 42.7 years old, and they all underwent interviews to collect data that included demographic, medical, household income, BMI, lifestyle, education and family history information.

Their blood samples were also taken to gain levels of fasting and postprandial (after meal) serum glucose, along with their glycated hemoglobin (hemoglobin linked with blood sugar). For the study, each participant was assigned an average exposure to artificial outdoor LAN for a specific location using night-time low-light image data of the Earth’s surface from the US Defense Meteorological Satellite Program (DMSP).

Exposure levels to the light were ranked from lowest to highest, and grouped into five quintiles (groups of 20% from highest to lowest), with the average light intensity in the highest quintile being 69 times greater than in the lowest. The exposure to the outdoor LAN varied throughout China, with most people being exposed to low intensity light.

The results

The study found that the highest quintile of outdoor LAN exposure was associated with an increase of 28% in the prevalence of diabetes than in the lowest quintile locations. Chronic exposure to outdoor LAN was associated not only with higher rates of the disease, but also higher blood glucose levels and insulin resistance. There was approximately one additional case of diabetes that would occur for every 42 people living in areas with the highest quintile of LAN exposure.

The study suggests that outdoor LAN is harmful and damaging to health. It can also allow researchers to consider the effect LAN can have on a global scale, with approximately 83% of the world’s population being exposed to outdoor light at night. Although there seems to be a correlation between light exposure and diabetes, the research team wants to further elaborate to see if the connections are directly related.