An increase in urinary volume at night may be due to an increase in the total 24-hour urine output, or to a higher percentage of the total daily urine output being excreted at night.
The increased urine production at nighttime may be nocturnal polyuria. Overproduction of urine at night, with a normal 24-hour urine output, is called nocturnal polyuria. The definition is age-dependent, and for older adults (>65 years) has been defined as nocturnal urine volume greater than 33 percent of the 24-hour urine volume. You may be asked to complete a 24-hour voiding diary to determine your daytime and nighttime urine production. Download “Nocturia Voiding Diary”
Nocturnal polyuria may be due to age-related changes in the secretion and action of arginine vasopressin (AVP). There is a fluctuation of AVP release in young, healthy subjects, with higher AVP plasma levels in the evening contributing to decreased nighttime urine output. This fluctuation in AVP release is absent in many older patients.
Poorly controlled diabetes and heart disease can also lead to nocturia. For diabetes, excess sugar in the bloodstream after a nighttime meal can cause more urine production at night. The increased blood glucose actually gets excreted in the urine where it “draws in” more water. This results in more urine production at night which causes nocturia.
For heart disease, congestive heart failure (CHF) can cause fluid to accumulate in your legs and around your ankles. At night when you elevate your legs in bed, it is easier for your heart to get rid of the fluid. This can result in nocturia.