Caffeine ingestion and lower urinary tract symptoms in healthy volunteers.

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

Materials And Methods: 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.

Results: 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.

Conclusions: 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.