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Caffeine intake and risk of stress, urgency, and mixed urinary incontinence
Ying H. Jura, M.D.1, Mary K. Townsend, ScD2, Francine Grodstein, ScD3.
1Massachusetts General Hospital, Boston, MA, USA, 2Harvard School of Public Health, Boston, MA, USA, 3Brigham and Women's Hospital, Boston, MA, USA.

BACKGROUND:
In this prospective study, we investigated the relationship between caffeine intake and incident urinary incontinence in 65,176 women 37 to 79 years old enrolled in the Nurses’ Health Studies. While previous epidemiological studies generally do not support caffeine as a risk factor for urinary incontinence, these studies have largely been cross-sectional, which could lead to bias if women with urinary incontinence reduce their caffeine consumption to improve their symptoms. Based on likely mechanisms of action, we hypothesized that caffeine intake would be particularly related to urgency incontinence.
METHODS:
Daily caffeine intake from food and beverages was calculated for each participant using dietary data reported on validated food frequency questionnaires administered every 4 years between 1980 and 2000 in the Nurses’ Health Study and between 1989 and 2001 in the Nurses’ Health Study II. The food frequency questionnaires distinguish between caffeinated and caffeine-free coffee and soda. To reduce measurement error and to better represent long-term habits, caffeine intake was defined as average intake across all the food frequency questionnaires from 1980-2000, or 1989-2001. New onset of urinary incontinence was identified from 2000 to 2004 in the Nurses’ Health Study and 2001 to 2005 in the Nurses’ Health Study II. We pooled data from the 2 cohorts and calculated multivariable-adjusted hazard ratios and 95% confidence intervals of the relation between caffeine intake and urinary incontinence risk, using Cox proportional hazard models adjusting for major incontinence risk factors, including age, body mass index, physical activity, total fluid intake, race, parity, cigarette smoking, and diabetes.
RESULTS:
Women with higher levels of daily caffeine intake had a statistically significant 9 to 24% increased risk of developing urinary incontinence at least weekly (adjusted RR 1.10, 95% CI 1.01 - 1.18 for 150-299 mg/day; RR 1.09, 95% CI 1.00 - 1.19 for 300-449 mg/day; RR 1.24, 95% CI 1.12 - 1.38 for ≥ 450 mg/day) compared to those with the lowest level of caffeine intake, 0-149 mg/day. This increase appeared largely explained by a significantly greater risk for incident urgency and mixed urinary incontinence (RR 1.28, 95% CI 1.00 - 1.63 for urgency incontinence; RR 1.44, 95% CI 1.14 - 1.81 for mixed incontinence, for ≥ 450mg/day). There was also a significant trend of increasing risk of urgency and mixed urinary incontinence (p for trend = 0.046 and 0.01, respectively) with increasing caffeine intake. There was no significant association between caffeine and stress urinary incontinence (p for trend = 0.22)
CONCLUSIONS:
Our findings suggest that higher daily caffeine intake is associated with modest increased risks of urgency and mixed urinary incontinence in women. These findings are consistent with caffeine’s known ability to stimulate smooth muscle contractions by mobilizing intracellular calcium stores. To our knowledge, this is one of only a few prospective epidemiologic studies on this topic. If our findings are confirmed in future studies, then self-monitoring and counseling to reduce caffeine intake might be considered to reduce the burden of incident urinary incontinence in women.


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