Light is an important environmental exposure because it is the main signal of the circadian system and factor in regulating the biological clock. Via the clock, exposure to light therefore has multiple effects on health. However, the different exposure models according to population groups have never been studied.
The study: The Boston team here analyzes light exposure in the real world, using trackers worn on the wrists of 11,314 participants in the NHANES (National Health and Nutrition Examination Survey, waves from 2011 to 2014), therefore on the database reflecting the duration and timing of exposure to different light levels (low/low, moderate and bright). The analysis delivers surprising results:
- men spend about 52% more time in bright light than women;
- this notable difference in exposure between the sexes begins in childhood and continues into adulthood;
- the first exposure of the day to bright light is also later for women, occurring about 30 minutes after men;
- among adults, time spent outdoors during work days seems to explain part, but not all, of this difference in exposure between the sexes;
- occupational factors contribute to these gender differences, in addition to other factors.
These data suggest possible effects on health -women- of this lower exposure to light: if the analysis did not seek to evaluate the consequences of low exposure to light, it is well known that light is the most important signal for the circadian system and that the intensity, duration and timing of light are characteristics that can affect the central clock (the suprachiasmatic nucleus) which transmits information to other biological clocks:
- exposure to dim or dim light has a weaker effect on the circadian system than bright light, meaning that dim light is not as effective at synchronizing biological clocks with the natural light/dark cycle;
- the synchronization of light exposure and the central biological clock also affects the functioning of the body (metabolism in particular);
- poor synchronization of body clocks can also negatively affect health outcomes such as the sleep-wake cycle and mood;
- sunlight is also important for vitamin D production, so limited exposure to daylight can promote vitamin D deficiency;
- Exposure to bright light during the day may have a protective effect against the harmful effects of nighttime light (although further research is needed).
Finally, the authors emphasize the importance of reasonable overall exposure to daylight, including spending more time outside in “outdoor” activities.
Health
