Exposure to light at night has significant effects on mental health and has been linked to, among other things, anxiety, bipolar disorder and depression. The risk of illness appears to increase significantly when exposed to light at night.
The current study by an international research team, the results of which were published in the specialist magazine “Nature Mental Health”, shows the far-reaching effects that light exposure has on mental health. Accordingly, night-time light is a clear risk factor for mental disorders, while daylight appears to reduce the risk.
Circadian rhythm disorders
With the invention of electric light, exposure to light at night has increased massively and today many people are exposed to various light sources well into the night. The result is disruptions to our internal biological rhythm (circadian rhythm), which in turn can cause further health problems.
For example, a study last year linked diabetes, high blood pressure and obesity to exposure to light at night. The study also revealed that less than half of the participants consistently spent five hours in complete darkness per night.
Psychological effects examined
The research team from Monash University (Australia), the University of Colorado (USA), the University of Manchester (UK) and Harvard Medical School (USA) examined the effects of light exposure on mental health in the current study using almost 87,000 participants examined by the UK Biobank.
Data from 86,772 people were analyzed for daytime and nighttime light exposure, sleep, physical activity and mental health. “We have carried out the largest cross-sectional analysis to date on light, sleep, physical activity and mental health,” emphasize the researchers.
Increased risk from nighttime light
According to the experts, higher exposure to light at night was associated with an increased risk of severe depressive disorders, generalized anxiety disorders, post-traumatic stress disorders (PTSD), psychoses, bipolar disorders and self-harming behavior.
These effects of nighttime light exposure were independent of demographic composition, physical activity, time of year and occupation, said study author Professor Sean Cain of Monash University.
“Our results were consistent even when taking shift work, sleep, urban or rural living and cardio-metabolic health into account,” adds Professor Cain.
Daylight reduces the risk
However, the researchers also found that, regardless of exposure to light at night, higher daytime light exposure was associated with a lower risk of major depressive disorders, PTSD, psychosis and self-harming behavior.
Those exposed to high levels of light at night had their risk of depression increased by 30 percent, while those exposed to high levels of light during the day had their risk of depression reduced by 20 percent, the research team reports.
Similar results can also be found for self-harming behavior, psychoses, bipolar disorders, generalized anxiety disorders and PTSD. Increased exposure to light during the day acts as a non-pharmacological means of reducing the risk of mental disorders.
Strengthening mental health
Apparently our brains have evolved to function best in bright light during the day and almost no light at night, explains Professor Cain. Avoiding light at night and seeking brighter light during the day could be an effective, non-pharmacological means of reducing serious psychological problems.
“These results can have enormous implications for society,” emphasizes Cain. If you understand that exposure to light has a strong impact on mental health, you can take a few simple steps to optimize your well-being. “It’s about bright light during the day and darkness at night,” summarizes the study author. (fp)