title: Factors affecting the nocturnal decrease in blood pressure: a community-based study in Ohasama.
abstract: OBJECTIVE
  To investigate factors affecting the nocturnal decrease in blood pressure.
  
  
  METHODS
  A cross-sectional study of 823 community-based untreated subjects aged > 20 years. Screening and ambulatory blood pressures were measured and the effects of age and the ambulatory blood pressure on the nocturnal decrease were examined.
  
  
  RESULTS
  The magnitude of the decrease and the percentage decrease in the nocturnal blood pressure increased with increasing daytime ambulatory blood pressure and decreased with increasing night-time ambulatory blood pressure. Although the magnitude of the nocturnal decrease in blood pressure increased with increasing daytime blood pressure, the nocturnal blood pressure levels in hypertensives were still higher than those in normotensive subjects. The magnitude decreased with increasing age for men but not for women, whereas the percentage decrease decreased with increasing age both for men and for women. The SD of the 24 h blood pressure correlated strongly to the magnitude of the nocturnal decrease (systolic blood pressure r = 0.62, P < 0.0001; diastolic blood pressure r = 0.52, P < 0.0001), suggesting that the SD of the 24 h blood pressure is representative of the nocturnal decrease. A minimal nocturnal decrease was observed frequently in elderly normotensive men but infrequently in hypertensive individuals from the general population. A marked nocturnal decrease was observed frequently in hypertensive women aged > 70 years.
  
  
  CONCLUSIONS
  Although the magnitude of the nocturnal decrease in blood pressure increased with increasing daytime blood pressure, the nocturnal blood pressure levels increased with increasing daytime ambulatory blood pressure. Therefore, the blood pressure in hypertensive subjects should essentially be lowered throughout the 24 h period. A marked nocturnal decrease in blood pressure in some elderly hypertensive women was observed without treatment. The nocturnal blood pressure levels of such subjects should be considered during treatment.
authors.affiliation: Department of Medicine, Tohoku University School of Medicine, Sendai, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Imai
authors.forename: A
authors.initials: A
authors.lastname: Nishiyama
authors.forename: T
authors.initials: T
authors.lastname: Ohkubo
authors.forename: I
authors.initials: I
authors.lastname: Tsuji
authors.forename: K
authors.initials: K
authors.lastname: Nagai
authors.forename: N
authors.initials: N
authors.lastname: Kikuchi
authors.forename: H
authors.initials: H
authors.lastname: Satoh
authors.forename: S
authors.initials: S
authors.lastname: Hisamichi
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology*; D002940:Circadian Rhythm; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D012044:Regression Analysis