Feasibility of overnight urine for assessing dietary intakes of sodium, potassium, protein and sulfur amino acids in field studies.

The feasibility of using overnight urine as an alternative to 24-hr urine was examined on measures of dietary intake of sodium (Na), potassium (K) and protein as well as the sulfur amino acids, which are contained mainly in animal protein. It was also of interest whether urinary excretions of taurine (Tau: final metabolite of sulfur amino acids, contained mainly in animal protein) and excretions of 3-methylhistidine (3-MHis: the product of breakdown of skeletal muscle protein, quantitatively excreted into urine) were appropriate in assessing the dietary intake of animal protein and total protein, respectively. Overnight urine specimens were collected from 16 subjects (19 to 60 years old) with normotension or borderline hypertension without complications. Creatinine (Cr) ratios to Na, K, urea nitrogen (UN) and inorganic sulfate (SO4) derived from overnight urine and from 24-hr urine specimens showed significant correlations. Similar correlations were also found for the Na/K and SO4/UN rations between overnight and 24-hr urine specimens. Concentrations of Tau and 3-MHis (mmol per g Cr) of overnight urine specimens were strongly correlated with 24-hr urinary excretions of Tau and 3-MHis (mumol per day), respectively. Furthermore, significant correlations were found between 24-hr urinary excretions of UN and 3-MHis and between those of SO4 and Tau. These results indicate that an overnight urine specimens are available for assessing dietary intakes of Na and K, as well as protein and sulfur amino acids in field studies.