Dr's Casebook: A glass of water might improve the quality of your sleep

Dr Keith Souter writes: I am sure you know the great tale written by Miguel de Cervantes in 1605. After a lifetime of reading books on chivalry day and night, the eccentric Don Quixote heads off on a rumbustious quest to become a wandering knight. As Cervantes says, ‘Finally, from so little sleeping and so much reading, his brain dried up and he went completely out of his mind.’

In that quote Cervantes gives an explanation for the character’s eccentricity. Too much reading, too little sleep and resulting dehydration seemed to dry his brain. Research by insomnia investigators suggests that there is a hint of truth here. They discovered that adults who sleep less than six hours per night, rather than eight hours, have more chance of being dehydrated. They suggest that those who don’t feel well after a night of poor sleep should consider dehydration as the cause, rather than actual insomnia.

In a huge study of over twenty thousand people in both the USA and China in 2018, they looked at how sleep affected the hydration status of individuals. They found that adults who reported sleeping less than six hours were up to 60 per cent more likely to be dehydrated than eight-hour sleepers. They had significantly more concentrated urine.

The reason for this is due to a hormone called vasopressin, which is important in regulating the hydration of the body. It is also called Antidiuretic hormone, or ADH and is secreted by the posterior pituitary gland under the brain. It stimulates water retention.

The scientists found that it is pumped out much faster and later on in the sleep cycle. People who have shorter sleep periods of six hours may be missing out on the later increased secretion of the hormone, resulting in the body getting more dehydrated.

So, taking a glass of water to bed and drinking if you wake in the night is a good idea, as is having a drink on waking.