title: Seasonal variations in nocturnal changes in blood pressure between Ireland and Singapore.
abstract: BACKGROUND
  Normal blood pressure (BP) follows a circadian rhythm, with dipping of BP at night. However, knowledge is limited in how the nocturnal dipping in hypertensive patients changes with the seasons. The study aims to examine the pattern of seasonal changes of nocturnal dip in an Irish population and furthermore, to compare it to the pattern observed near the equator where such seasonal variations are minimal, by also studying a Singaporean population.
  
  
  METHODS
  Ambulatory Blood Pressure Monitor recordings were obtained from 220 patients, half were from Mercy University Hospital, Cork, Ireland and half from the National Heart Centre, Singapore during the summer period from May to June and the winter period from October to December.
  
  
  RESULTS
  Irish seasonal changes resulted in an increase in nocturnal dipping in the hypertensive patients, especially for diastolic pressure (95% CI, 0.72 to 6.03, 3.37mmHg; p<0.05) and a change in the duration of dipping at night (95% CI, 0.045 to 1.01, 0.53h; p < 0.05). In Singapore, slight differences in dipping in systolic pressure were apparent despite the presence of only minor alterations in temperature (95% CI, 0.38 to 4.83, 2.61mmHg; P<0.05) or duration of daylight.
  
  
  CONCLUSIONS
  Seasonal changes not only affected the daily blood pressure but also the night time dipping status in hypertensive patients by mean value of 1.99mmHg and 3.38mmHg for systolic and diastolic pressure dip respectively. This has implications on how hypertensive patients should be treated during different seasons and when they are traveling to countries of different climatic environment.
authors.affiliation: College of Medicine and Health, University College Cork, Republic of Ireland.
authors.forename: Lin Ho
authors.initials: LH
authors.lastname: Wong
authors.affiliation: National Heart Centre, Singapore.
authors.forename: Peter
authors.initials: P
authors.lastname: Ting
authors.affiliation: Department of Pharmacology and Therapeutics, University College Cork, Western Gateway Building, Republic of Ireland.
authors.forename: David
authors.initials: D
authors.lastname: Kerins
keywords: Blood pressure; Hypertension; Nocturnal dip; Seasonal variation