Effect of vitamin D supplementation on urinary incontinence in older women: ancillary findings from a randomized trial.

BACKGROUND

Observational studies among older women have associated vitamin D insufficiency with a greater prevalence and incidence of urinary incontinence. However, little is known about the effect of vitamin D supplementation in reducing urinary incontinence.

OBJECTIVE

This study aimed to evaluate the effects of vitamin D supplementation in reducing the frequency of urinary incontinence in older women.

STUDY DESIGN

We conducted an ancillary study of women aged ≥55 years in the Vitamin D and Omega-3 Trial, a randomized trial with a 2×2 factorial design. Recruitment of participants started from 2011 to 2014 across 50 US states, and the follow-up of participants ended in January 2018. Randomized treatments in the parent study included (1) vitamin D (cholecalciferol) at a dosage of 2000 IU/d, (2) marine omega-3 fatty acids at a dosage of 1 g/d, and (3) matching placebo. Here, we analyzed women according to their randomization to vitamin D supplementation or placebo, regardless of treatment with omega-3 fatty acid supplementation. Validated frequency of urinary incontinence questions were added in year 2 of the study and were used again in year 5 at the end of trial. Prespecified ancillary outcomes included the prevalence of urinary incontinence at years 2 and 5, along with incident incontinence and progression of incontinence (from lower to higher frequency) from year 2 to year 5. Preplanned subgroup analyses examined the following outcomes: prerandomization of low serum levels of vitamin D (serum 25-hydroxyvitamin D<20 ng/mL), incontinence types, weight categories, and African American race.

RESULTS

Among the randomized women who provided urinary incontinence data, 11,646 women at year 2 and 10,527 women at year 5, the mean age was 70 years at year 2, with 29% racial and ethnic minorities. The prevalence of urinary incontinence that occurred at least weekly was 29% at year 2 and increased to 37% at year 5. Vitamin D supplementation compared to with placebo was not associated with lower odds of urinary incontinence occurring at least weekly at year 2 (odds ratio, 1.08; 95% confidence interval, 0.99-1.19) or year 5 (odds ratio, 1.04; 95% confidence interval, 0.94-1.15). Vitamin D supplementation compared to placebo was not associated with lower incidence or progression of urinary incontinence from year 2 to year 5: incidence (odds ratio, 1.06; 95% confidence interval, 0.83-1.35) or progression (odds ratio, 0.94; 95% confidence interval, 0.82-1.08). Women with prerandomization of low serum levels of vitamin D (n=836) did not have lower odds of the prevalence, incidence, or progression of urinary incontinence. The findings were null in subgroups according to incontinence type, women with obesity, and African American women. Only women with healthy weight randomized to vitamin D had lower odds of progression of urinary incontinence (odds ratio, 0.78; 95% confidence interval, 0.63-0.95; P=.01).

CONCLUSION

Vitamin D supplementation compared to placebo for 2 to 5 years was not associated with differences in the prevalence, incidence, or progression of urinary incontinence in older women with and without adequate serum vitamin D levels, with inconsistent differences among subgroups. The findings showed that the broad use of moderate doses of vitamin D supplementation did not reduce urinary incontinence in older women.