Caffeine ingestion and lower urinary tract symptoms in healthy volunteers

To assess lower urinary tract symptoms (LUTS) after caffeine ingestion in healthy volunteers.

We conducted a randomized, double-blind, placebo-controlled trial utilizing healthy adult volunteers without urinary tract disease. Caffeine dosage was based on patient weight (equivalent to a 70 kg person taking 200 mg of caffeine twice a day). After a 24-hr washout period, subjects ingested tablets (placebo and drug were identical in appearance) twice a day for 3 days. All participants completed volume-frequency diaries and a post-study symptom questionnaire. Statistical analysis was performed using SAS (version 8.2). Differences voiding frequency and volume were assessed by Wilcoxon rank sum test. The designated level of statistical significance was P < 0.05.

During the first day on study medications, patients taking caffeine versus placebo voided a mean of 7.8 versus 6.4 times in a 24-hr period, respectively, P = 0.05. The mean total urine production was 2,004 ml (caffeine) versus 1,643 ml (placebo), P = 0.06, while total fluid ingested was similar (2,246 ml-caffeine, 2,102 ml-placebo, P = 0.46). For the remaining 2 days there was no significant difference between the two arms. The post-study questionnaire revealed no differences in symptom perception between the two groups.

In healthy volunteers caffeine appears to produce an initial diuresis, but does not appear to have other significant or sustaining effects on lower urinary symptoms in this 4-day model.