Epidemiology studies have revealed that patients with obesity, hyperglycemia, or hypertension are associated with a decreased urine pH. These metabolic disorders are related to insulin resistance; however, the association between urine pH and insulin resistance remains unclear.
To evaluate this association while controlling for covariates, the present study was conducted in 1084 non-diabetic Japanese subjects undergoing health examination. Fasting urine pH was analyzed using an automated urine dipstick analyzer. The subjects were divided into five groups according to urine pH: those with pH <5.5, 5.5, 6.0, 6.5, and >6.5. Insulin resistance was determined using the homeostatic model assessment of insulin resistance (HOMA-IR) and divided into three categories: lower, middle, and higher tertiles of HOMA-IR. Analysis of covariance and multivariate logistic regression analysis were used to control confounding factors including serum uric acid.
Analysis of covariance showed an increase in the mean HOMA-IR from 1.26, 1.46, 1.69, and 1.75 to 1.89 with a decrease in urine pH (p<0.001). Subjects with urine pH ≤5.5 had a significantly higher HOMA-IR than those with urine pH>6.5. Furthermore, multivariate logistic regression analysis showed that urine pH had an inverse and independent association with HOMA-IR. In subjects with urine pH 5.5 and <5.5, adjusted odds ratio (95% confidence interval) for the incidence of higher tertile of HOMA-IR was 1.34 (1.04-1.73) and 1.52 (1.09-2.13), respectively (reference, subjects with a urine pH>6.5).
Insulin resistance is independently associated with a lower urine pH, possibly via lower formation of ammonium in the kidneys.