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A recent study warns us: too much exposure to artificial lights, especially at night, would disrupt the control of our glycemia, to the point of possibly promoting the development of type 2 diabetes.
If natural sunlight is, in general, good for health (for the circadian rhythm, morale or vitamin D, for example), it is also known today that exposing oneself to artificial light, in particular blue light is harmful in several ways: sleep disorders, vision, thyroid…
But a new Chinese study goes further: according to it, people who live in urban areas that are constantly lit at night also have higher blood sugar levels and react less well to insulin, the hormone that controls blood sugar. In question: illuminated windows and signs, car headlights, or even street lamps.
A 28% higher rate of diabetes for those most at risk
The extensive study was conducted on more than 98,600 people, men and women equally, living in 162 different areas. Researchers at Shanghai Jiaotong University in China divided these participants into five groups based on their exposure to light. A first observation is already striking: according to satellite data, the intensity of light for the 20% of people most exposed to light (in cities) was 69 times higher than that of people least exposed to light, in campaign.
The participants provided information on their medical and family situations, and their daily habits. Their body mass index (BMI) was calculated, and blood samples were taken to obtain fasting and post-meal glucose levels, as well as glycated hemoglobin, a form of glucose bound to hemoglobin that helps assess glycemic control. All these measures were followed over a period of 8 to 12 weeks. Results ? The study shows that people whose biological clock is the most disturbed by artificial light have a 28% higher rate of diabetes than people with the least exposure.
Disrupted pancreatic cells
How to explain the harmful effect of artificial light on blood sugar? The study, published in the journal Diabetology, gives a reason: the beta cells of the pancreas would work less well in people near artificial night light. However, it is the proper functioning of these cells that is at the origin of insulin, which itself controls blood sugar.
“People living in cities are more likely to move away from the 24-hour day-night rhythm to a pattern of work, late nights out, and exposure to artificial light at night. It is therefore essential to assess the importance of nocturnal artificial light linked to diabetes, in order to put in place effective prevention strategies. underline the authors of the study, who wish to continue their research, in order to categorize artificial light as a real factor in diabetes. So far, a correlation has been found, but that does not make it a causal factor.
A correlation but a causal link that remains to be demonstrated
We can also legitimately think that in urban areas (more enlightened), people have a diet and a physical activity different from those of the inhabitants of the countryside (less enlightened). And the study does not clearly state how these confounding factors were isolated when analyzing the results.
However, the study has the benefit of raising a new question about overexposure to light at night and its usefulness: turning off city lights at night, in addition to being a measure to preserve energy, could also allow to be to preserve health.