Seasonal influence on blood pressure in elderly normotensive subjects.

The aim of this study was to examine whether or not fluctuations in blood pressure (BP) differ by season. Subjects were 45 elderly individuals (20 men and 25 women; mean age, 66.5+/-4.9 [SD] years). Each subject's BP was recorded with an ambulatory BP monitoring device for 24 h during each of the four seasons. Subjects also wore a portable weather meter to obtain ambient temperature, relative humidity, and barometric pressure simultaneously with BP. The relationships between meteorologic values and BP were investigated at various parts of the day. Seasonal differences in BP fluctuation around wake-up-time were analyzed by means of the Tukey's test. The difference between the pre-wake-up-time systolic BP and the wake-up-time systolic BP was significantly greater in winter than in summer (8.7 mmHg greater, p<0.001). The difference between pre-wake-up-time and wake-up-time systolic BP was significantly greater in autumn than in spring (9.4 mmHg greater, p<0.001) or summer (13.1 mmHg greater, p<0.001). The difference between pre-wake-up-time heart rate and wake-up-time heart rate did not differ statistically between seasons. In conclusion, the present study showed that the difference between pre-wake-up-time systolic BP and wake-up-time systolic BP was greatest in the colder seasons, i.e., autumn and winter. There appears to be a large fluctuation in wake-up-time in the colder seasons. Low ambient temperature likely induces this large fluctuation.