A healthy person does not pass urine during sleep

Why? Because there is a refined mechanism that controls urine production during the night (night-time urine output).

The amount of urine produced during the night is 20-30% of the amount of urine produced over 24 hours.

An example

Take a person between 20 and 40 years of age (sex makes no difference). The amount of urine produced by the kidneys over a day, the 24-hour urine output, is divided into daytime urine output (produced during the 16 waking hours) and night-time urine output (produced during the 8 hours of sleep).

The amount of urine produced depends on kidney function, on the amount of fluid taken in and on the amount of fluid lost through sweating.

Suppose our person produces 1400 ml of urine in 24 hours: normally 1200 ml are produced and passed during the day, while 200 ml are produced during the night and passed with the first void in the morning.

Time

Awake 16 hoursAsleep 8 h

Urine

Daytime urine output 1200 ml200

Sleep takes up a third of the day, but only a seventh of the urine is produced at night.

The role of antidiuretic hormone

The reduction in urine production during sleep is linked to the release of a hormone by the pituitary gland: antidiuretic hormone (ADH) or vasopressin, which reduces the activity of the renal tubules.

The release of antidiuretic hormone is pulsatile: it increases during night-time sleep and decreases during waking hours. This rhythm is called the nycthemeral rhythm (night/day).

It is clear and intuitive that producing less urine at night allows continuous sleep, undisturbed by the annoying urge of a full bladder.

When, on the other hand, you wake up to pass urine, this is called nocturia.