When the temperature drops outside, blood pressure appears to rise in older adults, a new study shows.

The systolic (top number) and diastolic (bottom number) blood pressures both rose and fell with the change of seasons in the 8,801 people, aged 65 or older, looked at in the study by the Institut National de la Sante et de la Recherche Medicale of Paris. The average systolic blood pressure, for example, was five points higher in winter than in summer for the participants. Instances of high blood pressure (systolic blood pressure higher than 159, or diastolic higher than 94 millimeters of mercury or higher) were found in 33.4 percent of participants during winter but just 23.8 percent during summer.

The findings were published in the Jan. 12 issue of the Archives of Internal Medicine.

The reasons for the correlation, though, were not known. The authors said it could be related to the baroreflex, a mechanism of blood pressure regulation that is modified in elderly subjects or a function of the sympathetic nervous system, which helps control involuntary actions such as stress response.

Background information in the article said seasonal variance in blood pressure has been noted in past studies, but not specifically in the elderly.

"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 wrote.

(Agencies via China Daily January 14, 2009)