A disproportionate influence of fat mass accounts for the relationship between body mass index and lower urinary tract symptoms.
Lean mass had no influence on the risk of LUTS in the analysis of data from a large longitudinal cohort study.
"These findings suggest, therefore, that control of fat mass could lead to control of LUTS," said Carol Link, PhD, of the New England Research Institutes, Watertown, MA.
Investigators examined LUTS as a function of the individual influences of total fat mass, total lean mass, percentage fat mass, central fat mass, and central lean mass. The study population comprised 1,219 male BACH participants between ages 30 and 79 years.
Fat mass and lean mass were determined by dual x-ray absorptiometry (DXA); central fat and lean mass were calculated by subtracting appendicular lean and fat mass from the total body values. Presence of LUTS was based on the AUA symptom index (AUA-SI), and a score of ≥8 defined moderate/severe symptoms.
In the study group, the mean age was 50 years. The men had a mean BMI of 28.4, mean fat mass of 21.5 kg, mean lean mass of 53.6 kg, and mean height of 173.3 cm. The percentage of fat mass ranged between 5.7% and 48.3%. Of this group, about 20% had moderate or severe LUTS. The probability of moderate or severe LUTS increased with age, and BMI and LUTS had a U-shaped association.
Adiposity, LUTS associated
In multivariate analyses, total fat mass and percentage fat mass had a threshold association with LUTS. The estimated probability of LUTS increased rapidly with percentage fat mass in study participants who had ≥30% fat mass, about 75% of whom had a BMI of 29 or greater.
By contrast, increasing lean mass had a negative association with the probability of LUTS.
"Whether you look at total fat mass and lean mass or central fat mass and lean mass, the results are very similar," said Dr. Link. "The U-shaped association [between BMI and LUTS] is coming from the distribution of fat mass. Lean mass has little association with LUTS."
In another AUA presentation, Dr. Link and colleagues reported associations between urinary symptoms and various measures of obesity. The association is particularly relevant, given the increasing prevalence of both urinary tract symptoms and obesity and the aging of the U.S. population.
"Currently, 70% of Americans aged 30 to 79 are overweight and 35% are obese," Dr. Link noted.
Using data for 5,503 BACH participants (2,301 men and 3,202 women), investigators examined the joint association of age and adiposity on the prevalence of urologic symptoms. The best models included waist or hip circumference, rather than BMI.
Analysis showed that the association between urologic symptoms and adiposity is often U-shaped in men. For example, 30-year-old men with a waist circumference of 80 cm had the lowest prevalence of nocturia. In contrast, adiposity was the predominant influence on urologic symptoms in women, but its influence varied by age. For example, hip circumference at age 30 did not influence the prevalence of LUTS in women, but the prevalence of LUTS increases with hip circumference at age 80.
"If obesity continues to increase in the U.S., there will be more people with urologic symptoms than previously predicted," the authors concluded. "The gender differences on the effect of obesity and age on urologic symptoms suggest different pathophysiologic pathways. These results suggest that some urologic symptoms may be eliminated through weight reduction."