How longer summer days affect sleep cycles and behaviour

WITH the sun setting later and rising earlier during summer, UCT Sleep Science director Dr Dale Rae said this will impact your mood during the day, as well as your sleeping patterns and behaviour.

Rae said there were two main aspects that control sleep, the first is the longer you stay awake the more energy you need to recover when you sleep, and the second relates to people’s circadian rhythms which are the natural cycle of the physical, mental, and behaviour changes that the body goes through in a 24-hour cycle.

The matter of longer days and shorter nights informed the second.

Cape Town Weather Office forecaster Surprise Mhlongo said: “The sunset is mostly just before 8pm in summer months and close to 6pm during the other seasons of the year, meaning the sunset is closer to two hours later in summer months compared to other months of the year.

“The sunrise is mostly just after 6am in summer months and mostly just after 7am during the other seasons of the year, meaning the sunrise is closer to one hour earlier in summer.”

Based on this, Mhlongo said that people were experiencing slightly longer days in summer.

Rae said: “What is supposed to happen with regulative sleep is that when the sun goes down at night, your body starts to produce a hormone called melatonin which signals that it is sleep time to your body.

“If the sun goes down later, our body produces melatonin later which means we get the sleep signal later.

“We thus tend to get less sleep in summer than in winter.”

Rae said that if you were a person who was sensitive to sleep loss, and light as well, and you allowed yourself to have shortened sleep in summer, then you might feel more tired and moody.

But you could change this from a behavioural perspective.

“Sunlight and warmth promote better moods, so even though you might sleep a little bit less in the summertime, because of the warmth and the sunlight there are less low moods, depression etc.

“So even though there is more opportunity to sleep in winter, some people find that the lack of light exposure in winter can actually stimulate feelings of depression,” Rae said.