We are all aware of the Sun’s importance for life on Earth. Not only is it our key provider of energy, allowing us to stay warm and plants to photosynthesize, but it also delivers a variety of human health benefits, ranging from increased bone health to a strengthened immune system. This is thanks to the Sun’s role in our body’s synthesis of vitamin D, commonly known as the “sunshine vitamin”. Perhaps a somewhat unexpected side-effect of regular sunlight exposure is that it acts as a natural mood booster. Sunny days often bring with them a feeling of calm and content, but why is this?
Our mood is largely governed by the neurotransmitters serotonin and dopamine. Specifically, serotonin is essential for the maintenance of mood stability and sustained wellbeing, while dopamine, known as the ‘happy hormone’, is a key player in the brain’s reward system.
Aside from their critical role in mood maintenance, among cognitive functions such as learning and memory, these hormones can have additional effects in the human body: serotonin is largely produced in the gut and can have a significant impact on gut health if in shortage, while dopamine is involved in the regulation of pancreatic function. What’s more, vitamin D, which is produced in the skin upon sunlight exposure, is shown to be linked to the regulation of serotonin itself. Both serotonin and dopamine have been shown to increase in response to sunlight exposure, which explains the Sun’s ability to impact our mental health.
There are several examples illustrating the detriment that a lack of sunlight can bring to someone’s health. Seasonal affective disorder (SAD) is characterised by bouts of depressive symptoms at a particular time of year, usually winter, when the daily hours of light are limited.
This condition appears especially prevalent in areas with extended periods of darkness, such as the Arctic Circle- in the Northern regions of Finland, around 12% of the population is estimated to be affected by the disorder, with as many as 85% of Finnish adults reported to experience seasonal changes in their mood and sleeping patterns, according to Timo Partonen, a researcher at the Finnish Institute for Public Health and Welfare in Helsinki. Interestingly, the use of high-intensity lightboxes is emerging as a popular technique to combat SAD- this form of light therapy may be able to reverse the effects of a lack of sunlight.
Similarly, shift workers who are consistently awake during the night, and asleep during the light hours, are at an increased risk of developing mood disorders. The phenomenon known as Shift Work Disorder is brought on by the disruption to the circadian rhythm- one of the body’s natural internal clocks.
Normally, our sleep-wake cycles are in sync with the variation of light in our surroundings, so that when it gets dark, the brain starts to produce melatonin, the hormone acting as a cue for sleepiness. In contrast, light sends signals to the brain that result in feelings of alertness. Sustained disruption to the circadian rhythm, as seen in shift workers, not only leads to sleep problems but can also lead to low mood and irritability.
Although light therapy is not a comprehensive cure for mood disorders, it is without doubt that the sun’s rays can have a positive impact on how we feel. So make sure to get yourself outside next time the Sun is out!
Illustration: Verity Laycock