A Chinese study reports that exposure to artificial lighting at night is associated with poor blood sugar control and an increased risk of diabetes.
The life of most organisms, including humans, is governed by circadian rhythms that have developed in response to the Earth’s day-night cycle.
These rhythms, which roughly correspond to our sleep-wake cycle, create optimal time windows for activity, food intake and rest: during the day, our metabolism extracts energy from food to sustain during the day, while at night the excess energy stored in the form of glycogen and fat is used to ensure the functioning of vital organs during the fasting period.
It is somewhat the equivalent of working shifts in a factory: the various enzymes and metabolic hormones active during the day are at rest during the night, whereas conversely, those which come into action during the night become inactive during the day.
Disturbed cycles
This molecular choreography can obviously be greatly disturbed by artificial lighting at night.
We really like night lighting (we plan to install half a million lights in downtown Montreal this winter!), but it’s undeniable that this artificial light has an impact on our circadian rhythms.
The production of melatonin by the pineal gland, essential for promoting sleep, is obviously at the top of the list of targets for light pollution, but the metabolic impact that stems from disruptions in circadian rhythms should not be overlooked either.
For example, a meta-analysis of 12 studies that looked at this question reported that high exposure to artificial lighting at night was associated with a 13% increase in the risk of being overweight and a 22% increase in the risk obesity1.
Since more than 80% of the world’s population is exposed to light pollution2it is therefore possible that these disturbances may be responsible for a non-negligible proportion of the metabolic disorders currently observed.
Increased risk of diabetes
A recent study suggests that type 2 diabetes may represent another adverse metabolic effect of artificial lighting3.
In this study, researchers measured the blood glucose and glycated hemoglobin (a marker of chronic hyperglycemia) levels of 98,658 people in 162 cities in China.
In parallel, they determined the volunteers’ exposure to artificial light at night using satellite data from the US Defense Meteorological Satellite Program, which allowed them to separate the cohort into five quintiles of exposure (groups of 20%, from lowest to highest).
The study found that areas with the highest levels of artificial lighting (the highest quintile) had a 28% increased prevalence of diabetes compared to the lowest quintile.
Chronic exposure to artificial lighting was associated with increased blood sugar, insulin resistance, and type 2 diabetes, even after controlling for other factors that might have influenced this association.
Researchers estimate that 9 million cases of type 2 diabetes are directly attributable to exposure to light pollution, a number that is likely to increase even more in the coming years due to the increasing urbanization of Chinese society. .
Light pollution is a neglected problem in our modern societies, yet it is a source of significant health problems, both in terms of disruption of animal life cycles and human health.
1. Lai KY et al. (2020) Exposure to light at night (LAN) and risk of obesity: A systematic review and meta-analysis of observational studies. About. Res. 2020; 187:109637.
2. Falchi F et al. The new world atlas of artificial night sky brightness. Science. Adv. 2016; 2: e1600377.
3. Zheng R et al. Outdoor light at night in relation to glucose homoeostasis and diabetes in Chinese adults: a national and cross-sectional study of 98,658 participants from 162 study sites. Diabetologypublished on November 14, 2022.