Getting little sleep as a rule increases the risk of cognitive damage later in life. Those who sleep less than five hours are twice as likely to develop dementia as those who sleep an average of five hours seven hours.

Going to bed haphazardly (one day at ten at night; another, say, at 3 in the morning) causes a significant increase in risk of later suffering from Alzheimer's or other neurodegenerative ailments. People with little sleep during one season who, in other seasons, find their sheets sticking to them and then they sleep little again.