IT’S spring and you’ve probably noticed a change in when the Sun rises and sets. But have you also noticed a change in your mood? We’ve known for a while that light plays a role in our wellbeing. Many of us tend to feel more positive when spring returns.
But for others, big changes in light, such as at the start of spring, can be tough. Here’s what’s going on.
AN ANCIENT RHYTHM OF LIGHT AND MOOD
Light shining on the back of the eye sends “timing signals” to the brain and the master clock of the circadian system. This clock coordinates our daily (circadian) rhythms. “Clock genes” also regulate circadian rhythms. These genes control the timing of when many other genes turn on and off during the 24-hour, light-dark cycle.
BUT HOW IS THIS ALL LINKED WITH OUR MOOD AND MENTAL HEALTH?
Circadian rhythms can be disrupted. This can happen if there are problems with how the body clock develops or functions, or if someone is routinely exposed to bright light at night.
LIGHT ON THE BRAIN
Light may also affect circuits in the brain that control mood, as animal studies show. There’s evidence this happens in humans. A brain-imaging study showed exposure to bright light in the daytime while inside the scanner changed the activity of a brain region involved in mood and alertness. Another brain-imaging study found a link between daily exposure to sunlight and how the neurotransmitter (or chemical messenger) serotonin binds to receptors in the brain. We see alterations in serotonin binding in several mental disorders, including depression.
WHAT HAPPENS WHEN THE SEASONS CHANGE?
Light can also affect mood and mental health as the seasons change. During autumn and winter, symptoms such as low mood and fatigue can develop. But often, once spring and summer come round, these symptoms go away. This is called “seasonality” or, when severe, “seasonal affective disorder”.
Most people aren’t very seasonal. But for those who are, seasonality has a genetic component. Relatives of people with seasonal affective disorder are more likely to also experience seasonality.
Seasonality is also more common in conditions such as bipolar disorder. For many people with such conditions, the shift into shorter day-lengths during winter can trigger a depressive episode.
