Sleep Blog

The body’s production of urine follows a circadian rhythm, according to research presented at a recent conference. During the day, the body experiences greater urinary frequency, but at night, urine production declines, allowing most people to get uninterrupted sleep. The regulation of urine excretion during nighttime hours is influenced by many factors, including hormones, blood flow (hemodynamics), and sleep-related factors.

Although the exact mechanism behind the day vs. night urinary change is not yet understood, Danish researchers have examined the urinary patterns of sleep-deprived volunteers and have found a lack of sleep leads to increased urinary output with higher salt content. The findings were found to be more prevalent in males.

The Study

The study team is comprised of Birgitte Mahler, Kostantinos Kamperis, Soeren Hagstroem, Eva Radvanska, Soren Rittig, and J.C. Djurhuus, the Aarhus University Hospital, located in Denmark.

Mahler recently presented her team’s findings, entitled, “Sleep Deprivation and Nocturnal Urine Output - Gender Difference in the Effect,” at an American Physiological Society (APS) sponsored conference called, Sex and Gender in Cardiovascular-Renal Physiology and Pathophysiology.

Methodology

Twenty healthy volunteers (ten males; ten females; 19-35 years of age) underwent two 24-hour circadian in-patient studies under standardized conditions for diet and fluid intake. Participants were sleep deprived during one of the two sessions in a randomized sequence.

Their blood pressure and heart rate were recorded every hour using a non-invasive blood pressure monitor. Electrolytes, osmolarity, creatine and urea were evaluated in plasma and urine. Key blood elements were also measured. Excretions and clearances were calculated for electrolytes and osmoles.

Key Findings

There were no significant differences in the quantity or contents of the daytime urine examined in both experimental periods. Following the sleep deprivation period, however, both genders produced markedly larger amounts of urine. This effect was significantly more pronounced in males than females.

Sleep deprivation reduced the nighttime dip in blood pressure which can explain the lower levels of nighttime plasma rennin, angiotensin II and aldosterone and the increase in sodium and potassium excretion. The relatively higher blood pressure on sleep deprivation nights may also have affected the blood pressure in the kidney producing an osmotic diuresis.

The researchers found that during nighttime, acute sleep deprivation leads to:

• an increased urine output more evident in males
• a reduced fall in blood pressure (reduced nighttime dip)
• lower levels of sodium regulating hormones (plasma rennin, angiotensin II and aldosterone)
• excessive excretion of osmoles (sodium and potassium).

A change in the body’s hemodynamics, caused by sleep deprivation, seems to account for these observations.

The APS has been an integral part of the scientific discovery process since it was established in 1887. Physiology is the study of how molecules, cells, tissues and organs function to create health or disease.

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