Sleep Apnea and Frequent Nighttime Urination

Birmingham, AL

A breakthrough study has found that sleep apnea, a common but serious sleep disorder, is the root cause of nocturia, or getting up frequently during the night to urinate. Implications of the study, conducted by researchers at the University of Alabama at Birmingham (UAB), are particularly important for older adults who are at greater risk of falling and being hurt if they must get up frequently during the night to urinate. The study was published in the December 1999 issue of the journal Ostomy/Wound Management.

The findings may improve the diagnosis and treatment of sleep apnea and nocturia in older adults. "Sleep researchers know that nocturia is a sign of sleep apnea," says Mary Umlauf, Ph.D., associate professor of nursing at UAB and lead investigator of the study. "However, because the underlying mechanisms linking sleep apnea and nocturia had not been studied before, people with nocturia were more likely to report the problem to their gynecologist or urologist, not a sleep clinician. Doctors most often attribute nocturia to aging in women or to prostate problems in men."

What is Nocturia?

Nocturia can be defined as awakening from sleep to voluntarily urinate. It differs from enuresis or bed-wetting, where the person does not arouse from sleep, but the bladder empties anyway. Until recently, nocturia was thought to be caused by a full bladder, but it is also a symptom of obstructive sleep apnea. What actually causes nocturia is still being investigated. Some researchers believe that one event per night is within normal limits; two or more events per night may be associated with sleep deprivation.

How Apnea Causes Nocturia

Umlauf explains that during episodes of sleep apnea, the soft structures in the throat relax and close off the airway, setting into motion a chain of physiological events. "Oxygen decreases, carbon dioxide increases, the blood becomes more acidic, the heart rate drops and blood vessels in the lung constrict," says Umlauf. "The body is alerted that something is very wrong. The sleeper must wake enough to reopen the airway. By this time, the heart is racing and experiences a false signal of fluid overload. The heart excretes a hormone-like protein that tells the body to get rid of sodium and water, resulting in nocturia."

What Is Sleep Apnea?

This type of apnea is diagnosed when the airway obstruction lasts for 10 seconds or more, and occurs five or more times per hour of sleep. People with the most severe cases of sleep apnea can have more than 100 such events per hour of sleep. Symptoms include snoring, restless sleep with frequent awakenings, excessive daytime sleepiness, and morning headaches. Obesity may increase the likelihood of sleep apnea.

"It is a serious problem that, if left untreated, can be fatal," says Umlauf. "It can also have a significant negative impact on a patient's health and quality of life. It can lead to hypertension, impotence, heart disease, stroke and sudden death."

Apnea and Nocturia

The study, funded by the National Institute for Nursing Research, examined the sleep and nighttime urine production of 30 adults age 50 to 91 -- men and women, whites and blacks. "We found that diabetics and African-American women had more severe cases of sleep apnea and nocturia," says Umlauf. "Although more research is needed to validate our findings, it is clear that nocturia is not simply a prostate or age-related problem."

Sleep apnea, and the nocturia that accompanies it, are easily treatable with the use of a small bedside device (CPAP - continuous positive airway pressure) to maintain an open airway while asleep. "However, sleep disorders are often overlooked by doctors, because sleep medicine is a relatively new field," says Umlauf. "Doctors aren't normally trained about sleep disorders, so few ask if the patient is having signs of sleep apnea or other sleep symptoms."

Future Plans

Umlauf and her colleagues are planning a large-scale study to further examine the effects of treatment on nighttime urine production. "We are planning a rigorous study of treatment effects and have begun to present our findings widely among specialists in geriatrics, urology and women's health," says Umlauf. "It is too serious a problem to overlook."