It would seem that after the clocks went back and with the nights getting darker much earlier, a lot of us tend to want to sleep slightly more. For some this could be an association with the winter blues and even Seasonal Affective Disorder (SAD). For others it is seemingly just what happens.
Whilst there is no medical basis that we need more sleep in the winter than the summer, it may be that this is a natural change based on the shorter days, which are especially marked the further we get from the equator.
A recently published study by Friborg et al. (2011) supports the idea of seasonal variation in sleep due to daylight duration. The study compared Norway, a country that undergoes large seasonal variation, with Ghana, a country that undergoes very little seasonal variation (due to its position close to the equator). Seasonal effects were found for Norway, with bed and rising times being earlier in summer, whilst insomnia, fatigue and low mood were more prevalent in winter. These winter-summer seasonal differences were not found to be present for Ghana. Another study in Australia confirmed that we spend more time in bed in the darker months, including getting up later in the winter. This could be a seasonal adjustment from a biological perspective, a habitual change or simply down to the fact that it is colder and darker in the mornings. Therefore, less motivating to get out of bed. We are biological, psychological and social. We should view this in a holistic way.
So why do we feel more sleepy in the winter?
The reason behind being sleepier in the winter is that the exposure to light helps us maintain our circadian rhythm or body clock. When it gets dark our brain produces more melatonin, the hormone which gives us the desire to sleep. As it gets darker earlier in the winter, we naturally have the desire to go to sleep earlier. The darker days along with the colder temperature also encourage a lower metabolism during the winter. These facts lead to the longer sleeping time that we tend to spend in total in the longer winter nights.
However, this is as far as our physiology would have adapted with scientists certain that even if we had the propensity to have slept slightly longer in the winter, humans were not capable of hibernating. That said it is likely that our ancestors would have had a slow wind down process, once under shelter in the dark, mending clothes, storing food and doing chores rather than going to sleep straight away.
How Melatonin affects our sleep?
Concerning sleep quality, there is another complication in that in general the winter days are relatively gloomier than the summer days. This means that the distinction between day and night is less clear, which helps the early release of Melatonin. So, this can potentially happen during the day creating an increased ‘desire to sleep’ and often difficulty to stay awake and active once sleep is triggered.
How Vitamin D deficiency affects our sleep?
The decrease in daylight also lowers our natural production of Vitamin D, as less sunlight is hitting our skin. For those going to work before sunrise and leaving the office after sunset there is a higher risk of Vitamin D reduction. These reduced levels of vitamin D have been associated with greater levels of daytime sleepiness, and may influence Serotonin levels, which leads to fatigue and in some feelings of depression.
Old times vs Modern times way of sleeping?
Finally, most sleep experts now believe that we had biphasic sleep. Certainly, pre-19th Century it was common for people to have two 4-hour(ish) bursts of sleep broken by up to 4 hours awake. During this time they would often pray, talk or write by candle light and then go back to sleep once they felt the need, waking up at dawn. It is possible that the prevalence for biphasic sleep was increased in the winter.
In the modern day, with the electric light bulb we are less restricted after daylight hours than our ancient ancestors and equally we can put on the light straight away when the alarm goes off first thing.
Things to do to combat the darker days include…
• Get at least 10-15 minutes sunlight everyday
Preferably, 30 minutes in the sun every day. Exercising outdoors is a great way to do this. If you can’t do this and sit in an office try to sit by the window.
• Use an artificial light box
If you feel you are especially susceptible to the decreased light with decreased mood too then using an artificial light box might help lift your mood and get your body clock back on track.