With many regions of the United States having set or matched daily records for cold, prior to the winter solstice, it’s not a bad idea to possess a home blood pressure monitor because of the effect of cold weather on blood pressure BP. Seasonal variations in BP have been recognized and well documented in several research studies from the early 1980s through the late 1990s, but optimal use of the information derived from those studies cannot be achieved without the widespread use of home blood pressure monitor devices. By being aware of the seasonal changes in patients affected by this phenomenon doctors can make the appropriate adjustments to achieve and/or maintain good BP control and minimize the damaging effects of high BP on various parts of the body.
Research studies have shown an inverse relationship between environmental temperature and BP levels, with pressure readings being higher during cold weather and lower in warm and hot weather. A notable study conducted in France involved 8,801 adult patients greater than 65 years of age over a two-year period of time, during which time 33.4% of the individuals in the study had high BP readings during the winter compared to 23.8% during the summer. The elevated blood pressure readings during the winter were seen for both systolic and diastolic pressures but the study only reported the average systolic pressure elevation for the group, which was 5 points higher in the winter than in the summer.
Other studies performed using Best Blood Pressure Monitors or 24 hour ambulatory monitors have shown similar findings, with the most drastic variations in BP occurring in regions of the world with the most extreme seasonal changes in the temperature. The BP changes that occurred were similar between men and women studied.
The cause of this phenomenon, known in the health-care community as the seasonality of hypertension, is unknown, but a few theories have been proposed. One is that the sympathetic nervous system, which prepares the body to deal with stressful or emergency situations, is ramped up by cold weather which, in conjunction with decreased sodium excretion due to diminished sweating causes the BP to rise. The corollary hypothesis is that during warm and hot seasons larger amounts of sodium are excreted through sweating. The increased sodium excretion is accompanied by loss of fluid volume in the blood vessels, thereby reducing blood pressure.