Blood pressure measurement under standardized indoor condition may mask seasonal blood pressure variation in men with mildly elevated blood pressure

BACKGROUND: Blood pressure (BP) is generally higher in cold than in warm seasons. This seasonal BP change is largely attributable to outdoor temperature changes. However, if such a typical seasonal change is observed in BP measured under a standardized indoor condition remains unclear. METHODS: Resting supine BPs and heart rate (HR) were measured under a standardized room temperature during summer and the next winter in 104 untreated men (38.1 ± 4.4 years). Subjects were classified as having normotension (NT group: n = 79) or mildly elevated BP (ME group: n = 25) according to the summer measurements. Seasonal variation was defined as the difference from winter to summer measurements. We also examined body composition, endocrine parameters, and renal function. RESULTS: Age did not differ in the two groups (37.6 ± 4.2 versus 39.1 ± 4.9 years). The mean seasonal change in systolic BP was 2.7 ± 1.1 mmHg for the NT group and -4.6 ± 1.9 mmHg for the ME group (p = 0.001). Laboratory and outdoor temperatures did not differ between the two groups in either season. HR, noradrenaline, and estimated glomerular filtration rate were significantly higher during winter in the NT group but not in ME group. CONCLUSIONS: Typical seasonal change in BP may be masked in mildly elevated BP measured under a standardized indoor condition. The mechanisms are multifactorial. Our data suggest that out-of-office BP measurements are necessary for correctly understanding seasonal BP change especially in individuals with mildly elevated BP.