As urbanization is gradually taking over, the level of urban artificial lighting is likewise on the increase. Now, a new study has found that staying out late or just a casual walk down a well-lit neighborhood at night could accompany a host of health problems, including diabetes.
The scientists reveal that being exposed to artificial light at night may decrease the nighttime secretion of pineal melatonin, causing a disturbance in the normal timing of food intake and eventually affecting metabolic health. As a result, the blood glucose level is impaired leading to an increased risk of developing diabetes.
Prior experiments were performed on rats in which an elevated blood glucose level was found upon acute exposure to light at night. Another study involving mice found that exposure to even dim white light of little brightness for one month led to an increase in body mass along with glucose levels. However, the results differed among mice with no access to light despite having displayed similarities in total energy expended.
With the limited attention given to light pollution at night, researchers were curious to assess if there was a link between the extent of exposure to artificial lights at night and the risk of diabetes — for the need to put effective strategies in place.
The study published in the journal Diabetologia looked at data from a nationally representative sample of the total population in China. They focused on 162 study sites recorded in the China Non-communicable Disease Surveillance Study performed previously in 2010. A total of 98,658 Chinese adults who were above the age of 18 and were living in China partook in the survey. More than half of the participants were women, recording a total of 53,515. The team also targeted only those who had lived not less than 6 months in their recent home.
After this, the researchers interviewed all participants to gather data on their schooling, demographic characteristics, disease history, current medications, lifestyle habits, any record of family history of diabetes, and medical household income.
Next, they measured the body weight and height of the participants to calculate BMI. Participants were subjected to an overnight fast for not less than 10 hours. This was then followed by the collection of their blood samples to measure both fasting and 2h after-meal blood glucose concentrations along with glycated hemoglobin (HbA1c).
To determine the exposure levels of artificial outdoor light at night, the team made use of nighttime satellite imagery data supplied by the US Defense Meteorological Satellite Program. Carrying out further analyses, they grouped the participants according to the varying extent of light exposure into 5 different groups, ranging from lowest to highest exposure.
After adjusting for several diabetes risk factors, the study authors found that on average, for every 42 participants living in the region with great exposure to light, there was an added case of diabetes.
However, it is worth noting that the study authors say the link between diabetes and outdoor lights at night time exposure may not be as strong as risk factors that are more established e.g. obesity. Even so, a large number of people are exposed daily to residential lights at night.
They estimate that over 9 million cases of diabetes in Chinese adults could be attributable to exposure to outdoor light at night. On top of that, they point to other detrimental health effects associated with outdoor lights at night such as obesity, psychiatric disorders, and cancer.
Their findings, therefore, add to the growing body of evidence suggesting that light at night can harm overall health and contribute to the onset of diabetes.
“However, we advise caution against a causal interpretation of the findings and call for further studies involving direct measurement of individual exposure to LAN”, the authors conclude in the study.