When Night and Day Urination is “Night and Day”

Andrew Siegel MD     6/13/2020

Having some difficulties urinating during sleep time hours (often including the first urination of the morning upon awakening) while not really having any issues during the day is a common symptom that drives patients to see urologists.  Although this happens predominantly to men, it also can occur in women, so clearly, it is not just a matter of having a prostate gland.



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“Difficulties urinating” implies one or more of the following:

  • the need to push and strain to start or maintain the stream
  • a stream that is slow to start
  • a stream that is weak, and may spray or be forked
  • a stream that stops and starts
  • a stream that takes a prolonged time to empty
  • a sensation of incomplete emptying
  • the need to urinate a second time to feel satisfied


The seemingly simple act of urinating is actually an extremely complex physiological event. To urinate with a satisfactory stream, two things must happen: in a coordinated fashion, the bladder muscle must contract (squeeze) sufficiently and the sphincter muscles (those that provide control) must relax. The success of this is dependent upon an intact nervous system that governs contraction and relaxation of muscles as well as the ability of the bladder and sphincter muscles to properly contract and relax. If either bladder contraction or sphincter relaxation is compromised, the urinary stream will be deficient. The bottom line is that impairments in bladder contractility, sphincter relaxation, or both can hinder the ability to generate a strong urinary stream.

UNDERSTANDING THE STARLING CURVE (muscle length-tension relationship)

This fundamental principle of physiology helps to explain why nighttime peeing might be impaired in the face of normal daytime peeing.

THE STARLING CURVE: Muscle has lots of elastic fibers that allow the muscle to stretch and contract. The force of contraction of any given muscle is directly proportional to the stretch of that muscle. With increasing stretch there is more powerful  “snap,” up to a point, after which too much stretch leads to a decreased snap. See graph below:

starling curve(Frank-Starling relationship and length tension curve. Contributed by Chris BeardsleyFrom: Physiology, Starling Relationships  Copyright © 2020, StatPearls Publishing LLC., This book is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/)

To make this easier to understand, think about a rubber band or balloon:

Rubber band—stretch and release.  A small stretch will yield a small snap, a larger stretch will yield a larger snap, and a giant stretch will yield a damaged, flaccid rubber band.  Thank you to my partner Greg Lovallo for the rubber band metaphor.  As much as I enjoy using metaphors, Greg is unquestionably the “king” of metaphors. 

Balloon—blow it up with air and then release and let it fly.  A small volume of air will cause a small flight, a larger volume of air a more extensive flight, and too much air might pop the balloon.  Thank you to my partner Christ Wright for the balloon metaphor.


Thank you for image, FreeSVG.org


  1. The Starling Curve

The Starling curve is a key factor in selective nighttime vs. daytime urinary difficulties and is the underlying explanation for poor urinary flow in circumstances in which there is under- or over- bladder filling.

As the volume of urine in the bladder increases, so does the stretch of the elastic fibers of the bladder muscle. If you urinate with too small a volume of urine in the bladder (under-distension), you be unable to achieve enough stretch of the muscle fibers to obtain a powerful flow. If you urinate with an optimal volume of bladder filling– usually around 12 ounces or so–maximal contraction of the muscle will occur resulting in a powerful flow (in the absence of obstruction).  If you urinate with the bladder over-filled (over-distension), bladder contractility will be impaired and flow will thus be compromised.

Obstructive sleep apnea (OSA) is a common cause of nighttime urinary frequency, often large urinary volumes with poor flows. OSA affects 1/3 of men and 1/6 women, many of whom do not realize they are afflicted. Vigorous efforts to breathe against an obstructed airway—the cause of the snoring typical with OSA—cause negative pressures in the chest. Negative pressures pull venous blood from the abdomen and veins into the heart, causing distension of the right heart chambers. The heart responds to this distension–which is read as a false sign of fluid volume overload–by secreting atrial natriuretic peptide (ANP). ANP causes high volumes of urine production during sleep, resulting in sleep-disruptive, large volume nocturnal urinations in an effort to rid the body of the supposed fluid overloadThere may be as many as 6 or more nighttime awakenings to urinate, often with an impaired stream because of the high bladder volumes, the Starling curve in action.  The good news is that when OSA is treated, urinary symptoms improve dramatically.

Another factor is diminished proprioception (body awareness) while sleeping. One’s sense of desire to urinate can be diminished because of being in an unconscious state. This can lead to bladder over-distension and poor stream by virtue of the Starling curve

  1. Unrelaxed Sphincter Muscle

The striated sphincter is a muscle that is under voluntary control that when contracted will pinch the urethra and stop the flow of urine.  The action of squeezing this muscle is known as a “Kegel” or pelvic floor muscle contraction.

Skeletal muscles are often unrelaxed and even somewhat rigid in tone upon awakening in the morning.  As difficult as it would be to jump out of bed and start exercising immediately without limbering up, it can be equally challenging to relax the external sphincter immediately upon awakening, likely contributing to the complaint of selective first morning voiding difficulties. Upon arising, most people yawn a few times and do a big morning stretch to awaken the muscles that have gone into sleep mode. Likewise, after moving around a bit, the striated sphincter awakens and relaxes.

  1. The Many Mysteries of Nocturnal Physiology

Body functions vary during sleep time as opposed to wake time.  Circadian rhythms are the physiological changes that follow a daily cycle in response to light and darkness in the environment. There are a host of complex, poorly understood physiological changes that are simply different at night and with the assumption of a recumbent position.  Presumably, nocturnal physiological changes affect the urinary system as well as other bodily systems and may contribute to selective nocturnal urinary difficulties.

  1. Nocturnal and AM Erections

A healthy adult male has five or six phases of REM (rapid eye movement) sleep per night, commonly accompanied by a penile erection (REM erections).  Furthermore, many men awaken in the morning with an erection that occurs coincident with a full bladder (a.k.a. “piss hard-on” in lay terms). The rigidity and upward angulation of the penis can make urination challenging, contributing to nocturnal and first morning voiding difficulties. Erections facilitate ejaculation, but certainly not urination.

Wishing you the best of health,

2014-04-23 20:16:29


A new blog is posted weekly. To receive a free subscription with delivery to your email inbox visit the following link and click on “email subscription”:  www.HealthDoc13.WordPress.com

Dr. Andrew Siegel is a physician and urological surgeon who is board-certified in urology as well as in female pelvic medicine and reconstructive surgery.  He is an Assistant Clinical Professor of Surgery at the Rutgers-New Jersey Medical School and is a Castle Connolly Top Doctor New York Metro Area, Inside Jersey Top Doctor and Inside Jersey Top Doctor for Women’s Health. His mission is to “bridge the gap” between the public and the medical community. He is a urologist at New Jersey Urology, the largest urology practice in the United States.  His latest book is Prostate Cancer 20/20: A Practical Guide to Understanding Management Options for Patients and Their Families. 

4 small

Video trailer for Prostate Cancer 20/20

Preview of Prostate Cancer 20/20

Andrew Siegel MD Amazon author page

Prostate Cancer 20/20 on Apple iBooks

PROSTATE CANCER 20/20: A Practical Guide to Understanding Management Options for Patients and Their Families is now on sale at Audible, iTunes and Amazon as an audiobook read by the author (just over 6 hours). 

Dr. Siegel’s other books:

FINDING YOUR OWN FOUNTAIN OF YOUTH: The Essential Guide to Maximizing Health, Wellness, Fitness and Longevity

PROMISCUOUS EATING— Understanding and Ending Our Self-Destructive Relationship with Food

MALE PELVIC FITNESS: Optimizing Sexual and Urinary Health

THE KEGEL FIX: Recharging Female Pelvic, Sexual, and Urinary Health




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4 Responses to “When Night and Day Urination is “Night and Day””

  1. Joe Says:

    I really enjoy your weekly blog. I have a question; am a 76 year old with an almost constant ache in my right epidermis, your thought?

  2. 10 Reasons Men Sit to Pee (Maybe You Should Too!) | Our Greatest Wealth Is Health Says:

    […] Sufficient urine volume in bladder to optimize bladder contraction (Starling curve) […]

  3. Bubbly and Foamy Urine: Normal or Not? | Our Greatest Wealth Is Health Says:

    […] in the bladder (up to a point), the greater the speed and force of urination in accordance with the Starling principle. […]

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