title: Prognostic accuracy of day versus night ambulatory blood pressure: a cohort study.
abstract: BACKGROUND
  Few studies have formally compared the predictive value of the blood pressure at night over and beyond the daytime value. We investigated the prognostic significance of the ambulatory blood pressure during night and day and of the night-to-day blood pressure ratio.
  
  
  METHODS
  We did 24-h blood pressure monitoring in 7458 people (mean age 56.8 years [SD 13.9]) enrolled in prospective population studies in Denmark, Belgium, Japan, Sweden, Uruguay, and China. We calculated multivariate-adjusted hazard ratios for daytime and night-time blood pressure and the systolic night-to-day ratio, while adjusting for cohort and cardiovascular risk factors.
  
  
  RESULTS
  Median follow-up was 9.6 years (5th to 95th percentile 2.5-13.7). Adjusted for daytime blood pressure, night-time blood pressure predicted total (n=983; p<0.0001), cardiovascular (n=387; p<0.01), and non-cardiovascular (n=560; p<0.001) mortality. Conversely, adjusted for night-time blood pressure, daytime blood pressure predicted only non-cardiovascular mortality (p<0.05), with lower blood pressure levels being associated with increased risk. Both daytime and night-time blood pressure consistently predicted all cardiovascular events (n=943; p<0.05) and stroke (n=420; p<0.01). Adjusted for night-time blood pressure, daytime blood pressure lost prognostic significance only for cardiac events (n=525; p> or =0.07). Adjusted for the 24-h blood pressure, night-to-day ratio predicted mortality, but not fatal combined with non-fatal events. Antihypertensive drug treatment removed the significant association between cardiovascular events and the daytime blood pressure. Participants with systolic night-to-day ratio value of 1 or more were older, at higher risk of death, and died at an older age than those whose night-to-day ratio was normal (> or =0.80 to <0.90).
  
  
  CONCLUSIONS
  In contrast to commonly held views, daytime blood pressure adjusted for night-time blood pressure predicts fatal combined with non-fatal cardiovascular events, except in treated patients, in whom antihypertensive drugs might reduce blood pressure during the day, but not at night. The increased mortality in patients with higher night-time than daytime blood pressure probably indicates reverse causality. Our findings support recording the ambulatory blood pressure during the whole day.
authors.affiliation: Departamento de Fisiopatología, Hospital de Clínicas, Universidad de la República, Montevideo, Uruguay.
authors.forename: José
authors.initials: J
authors.lastname: Boggia
authors.forename: Yan
authors.initials: Y
authors.lastname: Li
authors.forename: Lutgarde
authors.initials: L
authors.lastname: Thijs
authors.forename: Tine W
authors.initials: TW
authors.lastname: Hansen
authors.forename: Masahiro
authors.initials: M
authors.lastname: Kikuya
authors.forename: Kristina
authors.initials: K
authors.lastname: Björklund-Bodegård
authors.forename: Tom
authors.initials: T
authors.lastname: Richart
authors.forename: Takayoshi
authors.initials: T
authors.lastname: Ohkubo
authors.forename: Tatiana
authors.initials: T
authors.lastname: Kuznetsova
authors.forename: Christian
authors.initials: C
authors.lastname: Torp-Pedersen
authors.forename: Lars
authors.initials: L
authors.lastname: Lind
authors.forename: Hans
authors.initials: H
authors.lastname: Ibsen
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Imai
authors.forename: Jiguang
authors.initials: J
authors.lastname: Wang
authors.forename: Edgardo
authors.initials: E
authors.lastname: Sandoya
authors.forename: Eoin
authors.initials: E
authors.lastname: O'Brien
authors.forename: Jan A
authors.initials: JA
authors.lastname: Staessen
mesh_terms: D000368:Aged; D001794:Blood Pressure; D018660:Blood Pressure Monitoring, Ambulatory / Q000379:methods / Q000706:statistics & numerical data*; D002318:Cardiovascular Diseases / Q000209:etiology* / Q000401:mortality; D002940:Circadian Rhythm; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D012307:Risk Factors; D016019:Survival Analysis