title: Urinary potassium is as reliable as urinary nitrogen for use as a recovery biomarker in dietary studies of free living individuals.
abstract: Twenty-four-hour urinary nitrogen (UN) is commonly used to validate dietary assessment methods. Potassium is more widespread in food than nitrogen, but the role of 24-h urinary potassium (UK) as a biomarker has been less studied and characterized. To investigate the performance of UK as a recovery biomarker compared with UN in subjects consuming their normal diet, 7 males and 6 females consumed known amounts of food based on their habitual varying diet (assessed beforehand from 4 consecutive 7-d food diaries) for 30 d in a metabolic suite. All daily urine samples and dietary duplicates were collected, and N and K were measured. Stool K was determined in 5-d pooled samples. Thirty-day mean analyzed K intake was 121.3 +/- 25.1 (mean +/- SD) mmol/d. Overall, 77 +/- 6.7% of K in the diet was excreted in urine and 18 +/- 5% in stool. Dietary K was correlated with UK (r = 0.89; P < 0.001). UN was 77.7 +/- 6.6% of N intake and was correlated with N in the diet (r = 0.87; P < 0.001). When 16 d of intake and 8 d of urine-collection measurements were randomly selected from the 30-d measurements, correlations were significant for both K (r = 0.86; P < 0.001) and N (r = 0.92; P < 0.001). The high correlations between UK and K in the diet show that UK is a reliable recovery biomarker for use in studies of dietary measurement error. Factors for use of urinary N as a recovery biomarker are also confirmed.
authors.affiliation: Medical Research Council Dunn Human Nutrition Unit, Cambridge CB2 2XY, UK.
authors.forename: Natasa
authors.initials: N
authors.lastname: Tasevska
authors.forename: Shirley A
authors.initials: SA
authors.lastname: Runswick
authors.forename: Sheila A
authors.initials: SA
authors.lastname: Bingham
mesh_terms: D000328:Adult; D000368:Aged; D015415:Biomarkers / Q000652:urine; D001835:Body Weight; D004032:Diet; D005243:Feces / Q000737:chemistry; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009043:Motor Activity; D009584:Nitrogen / Q000652:urine*; D011188:Potassium / Q000652:urine*; D015203:Reproducibility of Results; D013048:Specimen Handling / Q000379:methods
chemical_list: D015415:Biomarkers; D009584:Nitrogen; D011188:Potassium