Previous research has shown that blood pressure changes with the seasons, but few studies have looked specifically at old people.
For the study, Annick Alpérovitch, M.D., of the Institut National de la Santé et de la Récherche Médicale, Paris, and colleagues assessed the relationship between blood pressure and temperature in 8,801 individuals 65 or older.
Participants' blood pressure was measured at the beginning of the study (starting in 1999) and again about two years later. Outdoor temperatures on the day of measurement were obtained from local meteorological offices.
Both systolic (top-number) and diastolic (bottom-number) blood pressures differed across the four seasons and across the distributions of outdoor temperatures.
Average systolic blood pressure was 5 millimeters of mercury higher in winter than in summer.
High blood pressure-defined as a systolic blood pressure of 160 millimeters of mercury or higher, or a diastolic blood pressure of 95 millimeters of mercury or higher-was detected in 33.4 percent of participants during winter and 23.8 percent during summer.n average, each individual's blood pressure decreased between the initial and follow-up measurements. This decrease was also strongly correlated with outdoor temperature.
"The higher the temperature at follow-up compared with baseline, the greater the decrease in blood pressure," the authors said.
These differences over time were larger in participants age 80 and older.
"Mechanisms that could explain the association between blood pressure and temperature remain undetermined," the authors said.
The researchers suggest that the sympathetic nervous system (which helps control involuntary actions, such as stress response) is activated and the hormone catecholamine is released in response to cold temperatures, which may increase blood pressure by speeding the heart rate and decreasing the responsiveness of blood vessels.
"Although our study does not demonstrate a causal link between blood pressure and external temperature, the observed relationship nevertheless has potentially important consequences for blood pressure management in the elderly," the authors said.
The study is published in the January 12 issue of Archives of Internal Medicine, one of the JAMA/Archives journals. (ANI)