"In sleep surveys in our latitudes in Europe, 50 per cent of the respondents indicate they sleep 30-60 minutes longer in winter than in summer," says Prof Christian Cajochen of the University of Basel.
“Our sleep times were naturally regulated by the timing of dusk and dawn and they still are to a certain extent, but modulated by the use of artificial light.”
Therefore, daylight saving prolongs our sleep in autumn (ie from the last Sunday in October) and shortens it in spring (from the last Sunday in March).The flipside is that living closer to the equator naturally means less seasonal changes in sleep length and, in general, shorter nocturnal sleep: another reason why some people nap more often in those latitudes.
According to US clinical psychologist Dr Michael Breus, some people report that during winter they find their sleep is unrefreshing, while others report an increase in depression rates.
He says that owing to a lack of sunshine during winter, while people may be sleeping for longer hours, the quality of their sleep tends to be inferior.
“Natural light is the single biggest factor in our ability to wake up and, in many cases, to fall asleep,” Breus concludes.