Here’s a fact that most people do not know – when the temperature drops outside, blood pressure appears to rise. This information is critical for those with high blood pressure, a family history of high blood pressure, and for older adults. It means that people in both of these groups should have their blood pressure checked once or twice a month during cold weather months.
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This advice is bolstered by a new study reviewed by HealthDay News. The study found that 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.
The researchers, at the Institute National de la Sante et de la Recherche Medicale of Paris, reported that 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 this association are not known. However, it may be related to the baroreflex, a mechanism of blood pressure regulation, that may be more active in cold weather.
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.
SOURCE: JAMA, news release, Jan. 12, 2009