Urinary excretion of 3-methylhistidine and creatinine by healthy Dutch children during day and night. The influence of age and sex.

The urinary excretion of 3-methylhistidine and creatinine and the urinary 3-methylhistidine to creatinine excretion ratio during day and night were investigated in a group of 103 healthy, normally fed Dutch children (52 boys and 51 girls) aged 2-17 years. The 3-methylhistidine to creatinine ratio of the night urine appeared to be significantly higher than that of the urine produced during the day, irrespective of sex and age. This difference was about 30%. For both sexes it was found that the 3-methylhistidine and creatinine excretion increased and that the 3-methylhistidine to creatinine ratio decreased with age. Although the creatinine excretion by boys was significantly higher than that by girls of the same age, no differences were seen between the sexes with respect to the 3-methylhistidine excretion or the 3-methylhistidine to creatinine ratio. A clear linear relation was found between the day or night urine and the 24 h urine with respect to the 3-methylhistidine to creatinine ratio. However, no such relation was observed between the day and the night urine. These results are discussed in relation to the use of smaller urine samples instead of 24 hour urine in the study of 3-methylhistidine excretion.