A Danish study team found that sleep-deprivation might lead to increased urinary output and more salt in the urine. Normally, the body follows a circadian rhythm, producing greater amounts of urine during the day, and lessened production at night, enabling uninterrupted sleep.
Sleep deprivation, however, was found to change the body’s blood flow, leading to:
More frequent bathroom breaks in the middle of the night
A reduced fall in nighttime blood pressure
Higher salt content in the urine
The researchers speculate the reduced dip in nighttime blood pressure affects blood-pressure related substances, which in turn may keep the kidneys on a daytime schedule, hence the need to go to the bathroom during the night.
The American Physiological Society Press Release August 8, 2007
Reuters August 8, 2007
Science Daily August 8, 2007