Lack of sleep leads to increased urinary output and more salt in urine

Our body's production of urine follows a circadian rhythm. During the day, we experience greater urinary frequency; at night, urine production declines, enabling us 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. The mechanism behind the day/night changes is not yet clear. Danish researchers have examined the urinary patterns of sleep-deprived volunteers and have found that a lack of sleep leads to increased urinary output and more salt in urine. The findings were found to be more prevalent in males than females.

The Study
The study team is comprised of Birgitte Mahler, Kostantinos Kamperis, Soeren Hagstroem, Eva Radvanska, Soren Rittig, and J.C. Djurhuus, all of the Aarhus University Hospital, Brendstrupgaardsvej, Aarhus, Denmark. Dr. Mahler will present her team's findings, entitled, “Sleep Deprivation and Nocturnal Urine Output – Gender Difference in the Effect,” at the upcoming conference, Sex and Gender in Cardiovascular-Renal Physiology and Pathophysiology. The meeting, sponsored by the American Physiological Society (APS; www.The-APS.org), is being held August 9-12, 2007 at the Hyatt Regency Austin on Town Lake, Austin, TX.

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 American Physiological Society (APS; http://www.The-APS.org) 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.