Seasonal Variations in Blood Pressure

Talma Rosenthal, MD

Disclosures

Am J Geriatr Cardiol. 2004;13(5) 

In This Article

24-Hour Blood Pressure Monitoring

A few studies have examined seasonal variations in blood pressure by 24-hour ambulatory blood pressure monitoring (ABPM) or home blood pressure measurement.[25,26,27,28,29,30,31,32,33,34,35] The number of subjects in each study is relatively small,[18] although Giaconi et al.[26] studied 22 subjects in the high normal to mild hypertensive range and concluded that small studies can indeed detect seasonal influences, especially when ambulatory monitoring is used. The authors pointed out that the seasonal effects are confined to daytime. Only 10 young, normotensive women were investigated by Tsuchihashi et al.,[27] who repeated examination in spring, summer, autumn, and winter; there were no seasonal differences in young normotensives, although pulse rate during nighttime was significantly higher in winter (64±2 bpm vs. 59±2 bpm). According to Minami et al.,[30] nocturnal data showed that there was not a generalized winter elevation of blood pressure in individuals over the whole of the 24-hour period and that winter differences were restricted to the waking hours. Minami et al.[30] found that office, home, and daytime ambulatory blood pressure levels in 50 essential hypertensive patients aged 59.3±3 years were higher in winter than in summer; the differences were significant for daytime (3.5±1.4/2.5±0.8 mm Hg) but not for nighttime ambulatory blood pressure (-2.9±1.7/-1.2±1.0 mm Hg) or for average 24-hour blood pressure. In the large Hypertension and Ambulatory Recording Venetia Study (HARVEST),[36] which included mild hypertensives, 24-hour ABPM was done in both winter and summer in only 46 subjects, and seasonal differences were found solely in daytime.

In view of the known correlation between seasonal differences in blood pressure and changes in outdoor temperature,[7,11,25,26,28] Fujiwara et al.,[29] from Iwate in Japan, looked to determine whether there is a seasonal variation in blood pressure of essential hypertensive patients who live mainly in an indoor, air conditioned enviroment in a region where the summer-winter difference in temperature is only 6°C. Systolic and diastolic blood pressures in the morning and nighttime periods were significantly higher in winter than in summer (differences of 7.5±14.7 mm Hg and 4.1±8.8 mm Hg and 8.2±14.4 mm Hg and 4.5±8.1 mm Hg, respectively), and blood pressure measured in the afternoon and during sleeping periods did not differ significantly.

Kristal-Boneh et al.[31] found that controlled environmental conditions did not play a role in five factories, two of which were air conditioned and three were not. Workers exhibited significantly higher systolic blood pressures in winter than in summer by 3.4 mm Hg; higher daily systolic blood pressure circadian amplitude in winter, with higher mean systolic blood pressure during the day and lower mean systolic blood pressure at night; and higher daytime diastolic blood pressure measurements in winter than in summer and no seasonal differences at night. These same authors[33] note that the percentage of subjects with systolic blood pressure increases of more than 10 mm Hg from summer to winter was highest among subjects in the lowest body mass index category and lowest among those in the highest body mass index category (35% and 8%, respectively). Thus, according to these investigators, there is an inverse and independent association between increase in systolic blood pressure from summer to winter and body mass index. No such association was seen between diastolic blood pressure change and body mass index.

Brueren et al.[35] reported the absence of relevant seasonal influences on office and ambulatory blood pressure in borderline hypertensive primary care patients. Winter minus summer differences ranged from 0 to 3 mm Hg. Their single significant finding was significantly higher (3 mm Hg) ambulatory systolic daytime pressure in winter than in summer, leading them to claim that modifying antihypertensive treatment for borderline hypertensive patients according to season is not necessary. It must be remembered that this cohort consisted of borderline hypertensives, a group particularly prone to misclassification, overdiagnosis, and overtreatment, and that appears to take a position between normotensives (no seasonal influences) and hypertensives (significant seasonal influences). It should also be noted that the view of Brueren et al.[35] differs from that of the majority of investigators. Giaconi et al.[25] suggested that a possible bias from patient familiarization with such repeated measurements may enter this picture, as a higher seasonal difference in daytime blood pressure was observed for winter followed by summer vs. the reverse order.

In addition to relatively small cohorts, two large-scale series, one covering nearly 1000 subjects in the HARVEST trial[36] and another enrolling 2050 subjects in the Pressione Arteriose Monitorate E Loru Associazioni (PAMELA) study,[37] were cross-sectional studies in which different groups of matched subjects were studied in winter and in summer; one exception was a group of 46 subjects in the HARVEST sample who were studied in both summer and winter. The PAMELA[37] study investigated 2050 subjects who fell into three groups: normotensives, treated and nontreated patients examined at home, and patients examined in outpatient clinics and by 24 hour ABPM. In all three groups there was a significant seasonal difference in mean blood pressure both during the day and at night. The differences observed during ambulatory monitoring were smaller than those recorded in outpatient clinics and home blood pressure measurements.

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