Current perspective on seasonal variation in blood pressure

Blood pressure (BP) fluctuates within an annual cycle, with BP levels generally lower in summer and higher in winter. In this narrative review with a quasi-systematic literature search, we aim tosummarise current evidence from a wide variety of research fields on seasonal BP variability, andto present our findings to stimulate interest in this largely unexplored area. Environmental temperaturewould be the key driver of the seasonal BP variation, while other external and internal factorsmediate this variation; quantifying these effects is difficult because of the various factors and theirinteractions. Self-measured home BP would be the most favorable information for evaluating long-termseasonal BP changes. Nocturnal home BP reduction is lower in summer than in winter, leadingto a higher prevalence of the riser BP pattern in summer; we need to pay attention to the various riskfactors associated with higher BP across seasons. The temperature obviously affects BP; therefore,it seems reasonable to assume that seasonal BP changes linearly contribute to the seasonal mortalityvariation. However, our patients database showed that there are >10% of patients whose home BPis higher in summer than in winter, and the cardiovascular risk was significantly higher in patientswith such inverse seasonal variation, as well as in those with contrarily large-sized seasonal variationin home BP (≥9.1 mm Hg in systolic or ≥4.5 mm Hg in diastolic measurements) than in those withother small- to middle-sized seasonal variations. The inverse seasonal BP pattern is not rare in patientsunder antihypertensive drug treatment, and the mechanisms warrant investigation. Although theimportance of the BP level as a dominant and modifiable risk factor should be emphasized, assessingthe seasonal BP variation through long-term BP measurements, particularly based on home BPmonitoring, has clinical benefits and should be widely promoted.