title: Descriptive epidemiology of spot urine sodium-to-potassium ratio clarified close relationship with blood pressure level: the Nagahama study.
abstract: OBJECTIVE
  We undertook descriptive epidemiology of spot urine sodium-to-potassium ratio (Na/K) in a population sample to clarify the close relationship between Na/K and blood pressure level independently of potential confounding factors.
  
  
  METHODS
  Study participants consisted of 9144 apparently healthy citizens (aged 54 ± 13 years). All clinical parameters were obtained at baseline.
  
  
  RESULTS
  Na/K was significantly higher in hypertensive individuals irrespective of antihypertensive medication status (normotension, 3.12 ± 1.82; untreated hypertension 3.50 ± 1.96; treated hypertension, 3.72 ± 2.53). As urinary Na (β = 0.092, P < 0.001) and K (β = -0.050, P < 0.001) levels were inversely associated with BP, Na/K (β = 0.118, P < 0.001) was more closely associated with BP than Na or K alone, as well as daily salt intake estimated from urinary Na (β = 0.088, P < 0.001). Several factors were significantly associated with Na/K, namely age, sex, obesity, blood pressure, renal function, salt restriction status, serum phosphate and urinary creatinine level, and fasting period and season at urine sample collection. However, the association between Na/K and BP was independent of these factors (adjusted β = 0.112, P < 0.001). No direct association was observed between Na/K and large arterial remodeling assessed by pulse wave analysis (P = 0.496) or retinal arteriolar morphological change (P = 0.431). Further, a genome-wide association study failed to identify any particular genotype influencing urinary Na and K levels.
  
  
  CONCLUSIONS
  Although we clarified several factors that might affect spot urine Na/K, these relationships were not substantial enough to confound the association between urinary Na/K and BP. A simple measure of Na/K might be more representative of salt loading obtained from spot urine samples than Na excretion alone.
authors.affiliation: aCenter for Genomic Medicine, Kyoto University Graduate School of Medicine bDepartment of Health Informatics, Kyoto University School of Public Health cDepartment of Ophthalmology and Visual Sciences, Kyoto University Graduate School of Medicine dDepartment of Medical Ethics and Medical Genetics, Kyoto University School of Public Health, Kyoto eCenter for Preventive Medical Science, Chiba University, Chiba, Japan.
authors.forename: Yasuharu
authors.initials: Y
authors.lastname: Tabara
authors.forename: Yoshimitsu
authors.initials: Y
authors.lastname: Takahashi
authors.forename: Kyoko
authors.initials: K
authors.lastname: Kumagai
authors.forename: Kazuya
authors.initials: K
authors.lastname: Setoh
authors.forename: Takahisa
authors.initials: T
authors.lastname: Kawaguchi
authors.forename: Meiko
authors.initials: M
authors.lastname: Takahashi
authors.forename: Yuki
authors.initials: Y
authors.lastname: Muraoka
authors.forename: Akitaka
authors.initials: A
authors.lastname: Tsujikawa
authors.forename: Norimoto
authors.initials: N
authors.lastname: Gotoh
authors.forename: Chikashi
authors.initials: C
authors.lastname: Terao
authors.forename: Ryo
authors.initials: R
authors.lastname: Yamada
authors.forename: Shinji
authors.initials: S
authors.lastname: Kosugi
authors.forename: Akihiro
authors.initials: A
authors.lastname: Sekine
authors.forename: Nagahisa
authors.initials: N
authors.lastname: Yoshimura
authors.forename: Takeo
authors.initials: T
authors.lastname: Nakayama
authors.forename: Fumihiko
authors.initials: F
authors.lastname: Matsuda
mesh_terms: D000328:Adult; D000368:Aged; D001158:Arteries / Q000503:physiopathology; D001794:Blood Pressure; D005260:Female; D055106:Genome-Wide Association Study; D005838:Genotype; D006801:Humans; D006973:Hypertension / Q000453:epidemiology / Q000235:genetics / Q000503:physiopathology*; D007564:Japan / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D011188:Potassium / Q000652:urine*; D063177:Pulse Wave Analysis; D012964:Sodium / Q000652:urine*; D017673:Sodium Chloride, Dietary / Q000494:pharmacology; D012982:Sodium, Dietary; D066253:Vascular Remodeling
chemical_list: D017673:Sodium Chloride, Dietary; D012982:Sodium, Dietary; D012964:Sodium; D011188:Potassium