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Introduction:
Gender differences have been identified in uric acid (UA) urolithiasis. Intrinsic metabolic differences and BMI have been postulated as causative factors. We sought to evaluate whether diet may be responsible.
Materials & Methods:
We retrospectively reviewed 932 consecutive stone forming patients (543 men, 389 women) undergoing 24h urinalysis via Litholink at two tertiary care centers. Bivariate and multivariate regression analyses were used to identify significant associations.
Results:
Women had lower supersaturation of UA (0.84 vs 1.11, p<0.0001) despite lower volume (1.88 vs 2.01 L, p=0.02.) This was associated with lower absolute levels of UA (0.56 vs 0.72g, p<0.0001), sodium (147.1 vs 187.3mg, p<0.0001), and urinary markers of protein intake, sulfate (34.1 vs 47.2, p<0.0001) and urinary urea nitrogen (UUN) (9.9 vs 13.4, p<0.0001). Women had higher urine pH (6.14 vs 5.9, p<0.0001).
Evaluating the relationship of gender with dietary factors, female gender was associated with reduced UUN and sulfate (β= -3.6 and -13.1 respectively, p<0.001). On multivariate regression, it remained a significant predictor of decreased UUN and sulfate, even after adjusting for age, BMI, urine pH, and volume. (β= -2.8 and -10.5 respectively, p<0.001).
Conclusions:
Women had decreased UA supersaturation, associated with reduced absolute UUA and UA supersaturation. On univariate analysis, this is related to dietary factors (measures of protein intake) as well as protective potential metabolic factors (urinary pH). On multivariate analysis adjusting for pH, volume, age and BMI, we confirmed that dietary factors maintain a significant, independent role in gender-based differences in risk for UA stone disease