Seasonal Variation in Masked Nocturnal Hypertension: The J-HOP Nocturnal Blood Pressure Study

BACKGROUND Little is known about seasonal variation in nighttime blood pressure (BP) measured by a home device. In this cross-sectional study, we sought to assess seasonal variation in nighttime home BP using data from the nationwide, practice-based Japan Morning Surge-Home BP (J-HOP) Nocturnal BP study. METHODS In this study, 2,544 outpatients (mean age 63 years; hypertensives 92%) with cardiovascular risks underwent morning, evening, and nighttime home BP measurements (measured at 2:00, 3:00, and 4:00 am) using validated, automatic, and oscillometric home BP devices. RESULTS Our analysis showed that nighttime home systolic BP (SBP) was higher in summer than in other seasons (summer, 123.3 ± 14.6 mmHg vs. spring, 120.7 ± 14.8 mmHg; autumn, 121.1 ± 14.8 mmHg; winter, 119.3 ± 14.0 mmHg; all P<0.05). Moreover, we assessed seasonal variation in the prevalence of elevated nighttime home SBP (≥120 mmHg) in patients with non-elevated daytime home SBP (average of morning and evening home SBP <135 mmHg; n = 1,565), i.e., masked nocturnal hypertension, which was highest in summer (summer, 45.6% vs. spring, 27.2%; autumn, 28.8%; winter, 24.9%; all P<0.05). Even in intensively controlled morning home SBP (<125 mmHg), the prevalence of masked nocturnal hypertension was higher in summer (summer, 27.4% vs. spring, 14.2%; autumn, 8.9%; winter, 9.0%; all P<0.05). The urine albumin–creatinine ratio in patients with masked nocturnal hypertension tended to be higher than that in patients with non-elevated both daytime and nighttime SBP throughout each season. CONCLUSIONS The prevalence of masked nocturnal hypertension was higher in summer than other seasons and the difference proved to be clinically meaningful.