The day to day variations of urinary hydroxyproline (H. P) and creatinine excretion were investigated in five (two women and three men) healthy adults aged 28-42 years old under an ad lib. diet, collecting daytime and nighttime urine separately on 17-42 successive days. The daily protein intake of these subjects was also investigated, and the relation between daily H. P or creatinine excretion and daily protein intake was evaluated.
The following results were obtained:
1. Urinary H. P and H. P/creatinine have shown considerable day to day variations for all the five subjects (C. V 12.6-19.8% for H. P and 13.2-19.5% for H. P/creatinine). The day to day variation of creatinine excretion was much smaller than that of H. P (C. V 3.6-8.5%). The autocorrelation analysis of these time series suggested that there was no systematic temporal pattern.
2. In four out of five subjects, urinary H. P excretion during daytime and/or nighttime of a day showed significant positive correlations with the amount of protein intake on the same day or one or two days before. This finding suggests that the amount of urinary H. P excretion may be affected by dietary protein intake.
3. The difference of mean H. P excretion between daytime and nighttime was negligible in all five subjects.