Excessive abdominal visceral fat induces abnormal secretion of adipocytokines. This leads to an excessive production of various inflammatory cytokines, inducing systemic inflammation, and, ultimately, metabolic syndrome. The spread of systemic inflammation due to metabolic syndrome is the cause of various lifestyle diseases. Furthermore, metabolic syndrome has been recently reported to be an important factor affecting lower urinary tract symptoms, including overactive bladder (OAB). Several cross-sectional studies have shown associations between lower urinary tract symptoms and obesity and body mass index (BMI). However, no study has elucidated the relationships between an excessive accumulation of visceral fat, which triggers metabolic syndrome, and OAB morbidity and severity. Therefore, the present study aimed to clarify the relationship between the visceral fat level and OAB.

We targeted patients who underwent abdominal computed tomography (CT) during a health checkup and had not received treatments for lower urinary tract symptoms prior to the present study. Exclusion criteria were acute urinary tract infection and any condition affecting urinary function, including a history of pelvic surgery, benign prostatic hyperplasia, urethral stricture, urological malignancy, and neurogenic bladder. In addition, patients with incurable cancer were excluded.
Using the OAB symptom score (OABSS), we defined OAB as a score ≥ 2 on question 3 (urgency) and a total score ≥ 3. We examined the relationships of OAB and the total OABSS to the visceral fat area (VFA), visceral fat volume (VFV), subcutaneous fat area (SFA), subcutaneous fat volume (SFV), and total abdominal fat volume (TAV), as calculated on CT. Visceral fat measurements were performed using the three-dimensional image analysis system, SYNAPSE VINCENT (Fujifilm, Tokyo, Japan).

A total of 190 participants were enrolled (mean age, 60.4 ± 14.8 years). Ninety patients (47.4%) met OAB criteria. The mean age in the OAB group was higher than that in the non-OAB group (non-OAB group, 54.2 ± 15.2 years; OAB group, 67.4 ± 10.9 years; P < 0.001). In addition, the mean body weight in the OAB group was significantly higher than that in the non-OAB group (non-OAB group, 54.5 ± 10.2 Kg; OAB group, 57.6 ± 13.0 Kg; P = 0.035). However, the mean BMI was not significantly different between two groups (non-OAB group, 22.2 ± 3.5 Kg/m2; OAB group, 22.9 ± 4.7 kg/m2; P = 0.265). On abdominal CT, the non-OAB and OAB groups were significantly different in the VFA (73.8 ± 5.8 cm2 vs 112.1 ± 71.3 cm2, respectively; P < 0.001), VFA/SFA ratio (0.53 ± 0.29 vs 1.07 ± 0.97, respectively; P < 0.001), VFV (1860.8 ± 1234.5 cm3 vs 3167.3 ± 2269.9 cm3, respectively; P < 0.001), VFV/SFV ratio (0.52 ± 0.28 vs 1.55 ± 3.81, respectively; P = 0.008), and VFV/TAV  ratio (32.5 ± 10.6 vs 49.7 ± 14.3, respectively; P < 0.001). In addition, among the evaluated imaging factors, the VFV/TAV ratio had the strongest correlation to the total OABSS (r = 0.464, P < 0.001). In the receiver-operating characteristic curve for the VFV/TAV ratio and OAB, the area under the curve was 0.836. A sensitivity and specificity of 0.591 and 0.810, respectively, were obtained using a cutoff value of 0.591. Furthermore, a high VFV/TAV ratio (> 0.591) was an independent risk factor of OAB in the multivariate analysis (odds ratio, 4.66; 95% confidence interval, 1.03–33.2, P = 0.045), which included age, sex, VFV/TAV ratio, and high blood pressure, as these factors were significantly associated with OAB in the univariate analyses.

We evaluated the relationship between body fat volume and the presence of OAB. In the present study, there was no association between BMI and OAB, and the VFV was related to the presence of OAB rather than the VFA. Among the evaluated parameters, the VFV/TAV ratio had the greatest relationship to OAB symptoms. In addition, the VFV/TAV ratio correlated with the severity of OAB and was an independent risk factor of OAB. Together, these results suggest that an excessive accumulation of visceral fat, which triggers metabolic syndrome, increases the risk of OAB.

Although the present study is cross-sectional in nature, the results suggest that an excess accumulation of abdominal visceral fat is an important risk factor of OAB.