Inter- and intra-individual variations in normal urinary glycine betaine excretion

Objectives: To establish whether normal human subjects excrete glycine betaine at a constant rate. Design and methods: Urine was collected from ten normal healthy male subjects for 14 days, during which fluid intake was systematically varied from < 800 mL to > 3 L per day. Glycine betaine, sorbitol and creatinine excretions were estimated per day and as millimole per mol creatinine. Results: The intrasubject SD of urine glycine betaine was 3.5 mmol/mol creatinine, and the intersubject SD 5.8 mmol/mol creatinine. The intrasubject SD of plasma glycine betaine was 10.2 mol/L and the intersubject SD 14.2 mol/L. Water load had little effect on glycine betaine excretion and plasma glycine betaine. After 12 years, excretions and plasma concentrations tended to parallel the initial results. Conclusions: Normal subjects have consistent individual glycine betaine excretions that are not strongly influenced by urine volume. Abnormal excretions, or significant changes in excretion, can be interpreted as indicating a pathological process.