Determinants of 24-hour urinary oxalate excretion.
OBJECTIVE
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.


METHODS
We conducted a cross-sectional study of 3348 stone forming and non-stone-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.
Taylor
Eric N
EN
Renal Division and Channing Laboratory, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA. entaylor@partners.org
Curhan
Gary C
GC
D000328:Adult; D000367:Age Factors; D000368:Aged; D001205:Ascorbic Acid / Q000009:adverse effects; D015992:Body Mass Index; D001835:Body Weight; D002940:Circadian Rhythm; D003430:Cross-Sectional Studies; D048909:Diabetes Complications / Q000209:etiology* / Q000503:physiopathology / Q000517:prevention & control / Q000652:urine; D004032:Diet / Q000009:adverse effects*; D019587:Dietary Supplements / Q000009:adverse effects; D005260:Female; D005632:Fructose / Q000009:adverse effects; D006801:Humans; D007669:Kidney Calculi / Q000209:etiology* / Q000503:physiopathology / Q000517:prevention & control / Q000652:urine; D008274:Magnesium / Q000652:urine; D008297:Male; D008875:Middle Aged; D015596:Nutrition Assessment; D010070:Oxalates / Q000652:urine*; D010758:Phosphorus / Q000652:urine; D011188:Potassium / Q000652:urine
D010070:Oxalates; D010758:Phosphorus; D005632:Fructose; D008274:Magnesium; D001205:Ascorbic Acid; D011188:Potassium