Current perspective on seasonal variation in blood pressure

Blood pressure (BP) fluctuates with 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 to summarise current evidence from a wide variety of research fields on seasonal BP variability, and to present our findings to stimulate interest in this largely unexplored area. Environmental temperature would be the key driver of seasonal BP variation, while other external and internal factors mediate this variation; quantifying these effects is difficult because of the various factors and their interactions. Self-measured home BP would be the most favorable information for evaluating long-term seasonal BP changes. Nocturnal home BP reduction is lower in summer than in winter, leading to a higher prevalence of a riser BP pattern in summer; we need to pay attention to the various risk factors associated with higher BP across seasons. Temperature obviously affects BP; therefore, it seems reasonable to assume that seasonal BP changes linearly contribute to seasonal mortality variation. However, our patients database showed that there are >10% of patients whose home BP is higher in summer than in winter, and the cardiovascular risk was significantly higher in patients with such inverse seasonal variation as well as those with contrarily large-sized seasonal variation in home BP (≥9.1 mm Hg in systolic or ≥4.5 mm Hg in diastolic measurements) than in those with the other small- to middle-sized seasonal variation. The inverse seasonal BP pattern is not rare in patients under antihypertensive drug treatment, and the mechanisms warrant investigation. Although the importance of BP level as a dominant and modifiable risk factor should be emphasized, assessing seasonal BP variation through long-term BP measurement, particularly based on home BP monitoring, has clinical benefits and should be widely promoted.