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 during the winter months. These changes are more likely to occur the further we get from the equator.
A study by Friborg et al. (2011) compared Norway, a country that undergoes large seasonal variation in daylight, with Ghana. As Ghana is close to the equator it undergoes very little seasonal variation in daylight through the year. The study found seasonal effects in Norway. Bed and rising times are earlier in summer, and insomnia, fatigue and low mood more prevalent in winter, with winter tiredness certainly a feature. These winter-summer seasonal differences were not found to be present for Ghana.
A more detailed Australian study concluded that the association between winter and increased sleep could be a seasonal adjustment from a biological perspective (light dependent), a habitual change, or simply down to the fact that it is colder and darker in the mornings, and therefore less motivating to get out of bed. It was impossible to separate these individual biological, psychological and social impacts of winter from each other. All of these factors contribute individually and collectively to winter tiredness. However, the study confirmed that Australians spend more time in bed in the darker months, including getting up later in the winter.
Why do we feel more sleepy in the winter?
Absence of light is the major ‘initiator of sleep’ . Our body clocks and internal (circadian) rhythm are tuned to the planet through the natural cycle of day and light. When it gets dark our brain produces more of 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. Although this effect is now muted by our use of the light bulb at home in the evening. However, the darker days along with the colder temperature also encourage a lower metabolism during the winter. The combination of these factors could lead us to wanting to sleep more in the longer winter nights.
However, scientists are certain that even if we had the propensity to have slept slightly longer in the winter this is as far as our physiology would have adapted. Humans were not capable of hibernating.
How Melatonin affects our sleep?
Our grey winter days lack the clearer distinction between day and night that we enjoy during the summer. Thus, our brain can ‘leak’ Melatonin, the sleep hormone, during gloomy winter days creating an increased ‘desire to sleep’. For some this creates a difficulty to stay fully alert, especially in the natural siesta period in the early afternoon.
Reduced Vitamin D can also affect our sleep
Our natural production of Vitamin D is lower in the winter than the summer, as less sunlight hits our skin. This reduction in Vitamin D production is even more marked for those going to work before sunrise and leaving the office after sunset. Reduced levels of vitamin D are associated with greater levels of daytime sleepiness. Reduced vitamin D may also influence Serotonin levels, which leads to fatigue and in some feelings of depression.
The Chinese Way
Chinese medicine draws on the famous Yin and Yang to develop an interesting philosophy on the seasons – winter being the time a dark, slow, cold and an inward energy cycle occurs, forcing a reflection of the self. Here we would naturally observe that in winter as the days get shorter, we may feel like going to bed earlier and sleeping later because our body is signalling to us its need to heal and repair.
Some simple tips to combat ‘Winter Tiredness’
If you suffer from a decrease in energy in the winter here are three simple tips to try.
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
Take Vitamin D
This can help with depression too.
If you feel low and depressed
However, for some an increase in sleep in the winter could be an indication of ‘the winter blues’ or even the more severe depression call Seasonal Affective Disorder (SAD). If you think either could be the case visit your GP.