Determinants of 24-hour Urinary Oxalate Excretion

Abstract

Background and objectives: Higher levels of urinary oxalate substantially increase the risk of calcium oxalate kidney stones. However, the determinants of urinary oxalate excretion are unclear. The objective was to examine the impact of dietary factors, age, body size, diabetes, and urinary factors on 24-h urinary oxalate.Design, setting, participants, and measurements: We conducted a cross-sectional study of 3348 stone forming and nonstone-forming participants in the Health Professionals Follow-up Study (men), the Nurses' Health Study (older women), and the Nurses' Health Study II (younger women).Results: Median urinary oxalate was 39 mg/d in men, 27 mg/d in older women, and 26 mg/d in younger women. Participants in the highest quartile of dietary oxalate excreted 1.7 mg/d more urinary oxalate than participants in the lowest quartile (P trend 0.001). The relation between dietary and urinary oxalate was similar in individuals with and without nephrolithiasis. Participants consuming 1000 mg/d or more of vitamin C excreted 6.8 mg/d more urinary oxalate than participants consuming <90 mg/d (P trend < 0.001). Body mass index, total fructose intake, and 24-h urinary potassium, magnesium, and phosphorus levels also were positively associated with urinary oxalate. Calcium intake and age were inversely associated with urinary oxalate. After adjustment for body size, participants with diabetes excreted 2.0 mg/d more urinary oxalate than those without diabetes (P < 0.01).Conclusions: The impact of dietary oxalate on urinary oxalate appears to be small. Further investigation of factors influencing urinary oxalate may lead to new approaches to prevent calcium kidney stones.

DASH-Style Diet and 24-Hour Urine Composition

“…These results are consistent with our previous quantification of the independent association between dietary and urinary oxalate in these study populations (26). The small effect of dietary oxalate on urinary oxalate may reflect the primacy of endogenous oxalate synthesis in determining urinary oxalate levels and is consistent with the modest or null associations we previously observed in these cohorts between dietary oxalate and kidney stone formation (19).…”

Demographic, Dietary, and Urinary Factors and 24-h Urinary Calcium Excretion

“…Participants in the highest quartile of urinary potassium excreted 49 mg/d (39 to 59; P trend Ͻ0.001) less urinary calcium. We previously reported the inverse association between urinary oxalate and urinary calcium (26).…”

A comparison of the metabolic profiles of diabetic and non-diabetic uric acid stone formers

“…13 This work demonstrated consistently higher urinary oxalate levels in diabetic patients, a finding that was durable despite controlling for both dietary oxalate and calcium. 13 Although the pathophysiology of this relationship has not been fully delineated, it has been proposed that increased BMI and diabetes leads to changes in the metabolism of oxalate or an increase in endogenous oxalate production. 14 Hyperoxaluria has also been identified in hypertensive non-obese stone formers, although there is no indication whether any of the patients in the series were also diabetic.…”