What causes nighttime urination?

Dear Dr. Roach: I am a 68-year-old female. I’m in good health and take no medications. I urinate at 5:30 a.m., once at lunch and once before bed, and I do not drink any beverages after 6 p.m. If I can go that many hours without urinating during the day, why do I have to get up in the night to urinate two to four hours after lying down? — A J

You have already made one important change recommended for a person with annoying nighttime urination (nocturia), which is not drinking after 6 p.m. So let’s explore other reasons you still might be having this problem.

Needing to urinate at night is common, especially for older people of both sexes. For men, prostate issues are one problem, while in women, it is loss of estrogen that seems to be the predisposing factor. Treatment with vaginal estrogen often is effective for women with nocturia. Both men and women can have other causes.

Swollen ankles and feet is a symptom in people with kidney or heart disease, but it can be present in many older people without known disease. Lying down allows this fluid to go back into the blood, at which point the kidneys excrete that fluid as urine. Support stockings can reduce this effect.

The body also uses a hormone (arginine vasopressin, also called anti-diuretic hormone) to reduce nighttime urination. In some older people, that system stops working properly and the body actually increases urine output at night. Younger people can be treated with a nasal preparation of this hormone, but that is not recommended in people over 65 due to the unacceptably high rate of low blood sodium levels.

Some people wake up due to a sleep problem (especially obstructive sleep apnea) and then urinate, rather than waking up because of the need to urinate. That diagnosis should be considered.

Write to Dr. Roach at ToYourGoodHealth@ med.cornell.edu or mail to 628 Virginia Dr., Orlando, FL 32803.