Obesity, aging swell prevalence of lower urinary tract symptoms, nocturia

October 1, 2008

Prevalence of symptoms is influenced by adiposity, but in different ways in men and women, suggesting a different pathophysiology of LUTS in men and women.

Orlando, FL-With the American population not only aging, but also becoming more obese, urologists will be treating far more patients with lower urinary tract symptoms than those accounted for in the epidemic proportions already projected for 2025.

That's one of the conclusions of an analysis of the National Institutes of Health-funded Boston-Area Community Health (BACH) Survey Epidemiologic Study data that Carol Link, PhD, presented at the 2008 AUA annual meeting. Dr. Link is a senior research scientist at the New England Research Institutes in Watertown, MA.

Dr. Link pointed out that because many adiposity measures are highly correlated, it was difficult to say which measurement is best to correlate with age and LUTS. She focused on waist circumference.

Without considering adiposity, the prevalence of one of the most bothersome lower urinary tract symptoms that correlates with age is nocturia. The BACH data for nocturia, defined as two or more voids per night, rose fairly linearly for both men and women. At younger ages, however, women were more likely than men to have nocturia; at older ages, the sexes suffer fairly equally from nocturia. In women, the prevalence rises from about 24% in the 30s to 45% in the 70s. In men, the prevalence is about 16% in the 30s and rises to 42% in the 70s.

However, when Dr. Link used waist circumference as the independent variable, the patterns for men and women looked very different. In women, prevalence of nocturia rose sharply in correlation with waist circumferences of 60 cm to about 120 cm, then flattened from that point to 140 cm.

In men, nocturia became less prevalent as waist circumference rose from 60 cm to about 80 cm, then grew only slightly as waist circumference increased to about 110 cm, rising sharply as waist circumference increased beyond 110 cm. The correlation describes a U-shaped curve on a plot of nocturia against waist circumference.

Although nocturia was more prevalent in older age groups, these patterns of nocturia in relationship to waist circumference held for men and women across the decades.

Adiposity and LUTS

The same pattern in relation to obesity emerged for men when Dr. Link analyzed overall LUTS, as determined by an AUA Symptom Index score of 8 or more against hip circumference as the independent variable. The U-shaped curve emerged with higher prevalence at each decade from 30 to 60, staying constant at 70 and decreasing slightly at 80.

However, the obesity pattern for women differed from the model based on nocturia and waist circumference.

"At age 30 in women, the line is flat. Adiposity doesn't matter," Dr. Link explained. "However, if you're near 80, it matters a great deal." For that older age group, the prevalence of LUTS rose linearly and sharply with increasing hip circumference.

What does that imply for urologic practice? For patient counseling, the answer is not yet clear because, as Dr. Link emphasized to the audience, these are only associations; they don't show causality. Nevertheless, urologists can at least tell their female patients that the relationship of urinary symptoms with obesity strengthens as they age. It may add to the growing list of good reasons for patients to control their weight as they age.

What urologists can count on is a large increase in patients with urologic symptoms in the coming years. What's less clear is whether there will be enough urologists to care for them.