title: Seasonal variation in natural abundance of 2H and 18O in urine samples from rural Nigeria.
abstract: The doubly labeled water (DLW) method is used to measure free-living energy expenditure in humans. Inherent to this technique is the assumption that natural abundances of stable isotopes (2)H and (18)O in body water remain constant over the course of the measurement period and after elimination of the loading dose of DLW will return to the same predose level. To determine variability in the natural abundances of (2)H and (18)O in humans living in a region with seasonal shifts in rain patterns and sources of drinking water, over the course of 12 mo we collected weekly urine samples from four individuals living in southwest Nigeria as well as samples of their drinking water. From ongoing regional studies of hypertension, obesity, and energy expenditure, we estimated average water turnover rate, urine volumes, and sodium and potassium excretion. Results suggest that (2)H and (18)O in urine, mean concentrations of urinary sodium and potassium, urine volume, and total body turnover differed significantly from dry to rainy season. Additionally, seasonal weather variables (mean monthly maximum temperatures, total monthly rainfall, and minimum relative humidity) were all significantly associated with natural abundances in urine. No seasonal difference was observed in drinking water samples. Findings suggest that natural abundances in urine may not remain constant as assumed, and studies incorporating DLW measurements across the transition of seasons should interpret results with caution unless appropriate doses of the tracers are used.
authors.affiliation: Division of Epidemiology, Department of Public Health Sciences, Loyola University School of Medicine, Maywood Illinois; jharbison@luc.edu.
authors.forename: Justin E
authors.initials: JE
authors.lastname: Harbison
authors.affiliation: Division of Epidemiology, Department of Public Health Sciences, Loyola University School of Medicine, Maywood Illinois;
authors.forename: Lara R
authors.initials: LR
authors.lastname: Dugas
authors.affiliation: Department of International Health, Bloomberg School of Public Health, John Hopkins University, Baltimore Maryland;
authors.forename: William
authors.initials: W
authors.lastname: Brieger
authors.affiliation: Division of Epidemiology, Department of Public Health Sciences, Loyola University School of Medicine, Maywood Illinois;
authors.forename: Bamidele O
authors.initials: BO
authors.lastname: Tayo
authors.affiliation: Geospatial Laboratory, Research for Development, International Institute of Tropical Agriculture, Ibadan, Nigeria;
authors.forename: Tunrayo
authors.initials: T
authors.lastname: Alabi
authors.affiliation: Department of Nutritional Sciences, University of Wisconsin, Madison, Wisconsin.
authors.forename: Dale A
authors.initials: DA
authors.lastname: Schoeller
authors.affiliation: Division of Epidemiology, Department of Public Health Sciences, Loyola University School of Medicine, Maywood Illinois;
authors.forename: Amy
authors.initials: A
authors.lastname: Luke
mesh_terms: D001834:Body Water / Q000378:metabolism; D002980:Climate; D003903:Deuterium / Q000652:urine*; D060766:Drinking Water / Q000032:analysis; D004734:Energy Metabolism / Q000502:physiology; D005260:Female; D006801:Humans; D007553:Isotope Labeling; D008297:Male; D008875:Middle Aged; D009549:Nigeria; D010103:Oxygen Isotopes / Q000652:urine*; D011188:Potassium / Q000652:urine; D011891:Rain; D012424:Rural Population; D012621:Seasons; D012964:Sodium / Q000652:urine; D014563:Urodynamics / Q000502:physiology
chemical_list: D060766:Drinking Water; D010103:Oxygen Isotopes; D012964:Sodium; D003903:Deuterium; D011188:Potassium
keywords: Nigeria; doubly labeled water; seasonal variation