In this latest video from MedCram, Dr. Seheult explores the significant impact of light exposure on mortality rates. He delves into the science behind how light — or the lack of it — can influence human health and well-being, offering important implications for our daily routines, healthcare practices, and even public policy.
Dr. Seheult discusses how during the day it is important to have light exposure to your eyes to anchor your circadian rhythm. At night it is important to not have any type of light coming into your eyes as it can shut down melatonin production. Up to this point there have been a multitude of observational studies. He reviews a study from China that found a positive association between light at night (LAN) and all natural cause-specific mortality, of which the strongest effect was observed on mortality caused by neuron system disease. It had a relative risk of 1.32 and this was within the 95% confidence interval. The authors conclusion was that LAN in China was associated with an increase for neuron system disease related mortality. This was an associative study. A critique of this study is that light at night itself doesn’t tell us how much light the person was getting.
However, another study was recently published that predicted higher mortality risk with a dose dependent increase in mortality. This study involved wearing a light-sensor watch for 1 week which was reflective of how much personal light an individual received. These individuals were then tracked for 8 years and were tracked on their mortality and causes. The study had three models that adjusted for a variety of factors. Model 1 adjusted for age, sex, ethnicity and photo period. Model 2 added employment status, education, income and deprivation. Model 3 added in addition physical activity, smoking status, alcohol consumption, urbanicity and social activity. The reference here is looking at light exposure at night. The study was set up to show a dose dependent response curve which would be highly suggestive of causation. The study found that light during the day was very important and probably even more than avoiding light at night. The more light you are exposed to during the day and the least amount of light you are exposed to at night is highly conducive to living longer. The best way to do this is to not spend your entire day inside. The study concluded that the findings demonstrated the importance of maintaining a dark environment across the late night and early morning hours when the central circadian pacemaker is most sensitive to light and seeking bright light during the day to enhance circadian rhythms.
MedCram encourages you to try and get as much light exposure during the daytime and to limit it at night.
LINKS / REFERENCES:
Brighter nights and darker days predict higher mortality risk: A prospective analysis of personal light exposure in 88,000 individuals (PNAS) | https://www.pnas.org/doi/epub/10.1073…
Light at night and cause-specific mortality risk in Mainland China: a nationwide observational study (BMC) | https://bmcmedicine.biomedcentral.com…