Relationship between blood pressure and outdoor temperature in a large sample of elderly individuals: the Three-City study.

BACKGROUND Seasonal variations of blood pressure-related diseases have been described in several populations. However, few studies have examined the seasonal variations of blood pressure in the elderly, a segment of the population particularly exposed to vascular diseases. The association of blood pressure with season and outdoor temperature was examined in 8801 subjects 65 years or older from the Three-City study, a population-based longitudinal study. METHODS Blood pressure was measured at baseline and 2-year follow-up examinations. Daily outdoor temperature measured at 11 am was provided by the local meteorological offices. RESULTS Both systolic and diastolic blood pressure values differed significantly across the 4 seasons and across the quintiles of the distribution of outdoor temperature. Systolic blood pressure decreased with increasing temperature, with an 8.0-mm Hg decrease between the lowest (< 7.9 degrees C) and the highest (> or = 21.2 degrees C) temperature quintile. Intraindividual differences in blood pressure between follow-up and baseline examinations were strongly correlated with differences in outdoor temperature. The higher the temperature at follow-up compared with baseline, the greater the decrease in blood pressure. Longitudinal changes in blood pressure according to difference in outdoor temperature were larger in subjects 80 years or older than in younger participants. CONCLUSIONS Outdoor temperature and blood pressure are strongly correlated in the elderly, especially in those 80 years or older. During periods of extreme temperatures, a careful monitoring of blood pressure and antihypertensive treatment could contribute to reducing the consequences of blood pressure variations in the elderly.