SEASONALITY IN NIGHT-TIME BLOOD PRESSURE AND ITS ASSOCIATIONS WITH TARGET ORGAN DAMAGE

Abstract

Objective: There is some evidence that nighttime blood pressure varies between seasons. And it is unclear if the higher nighttime blood pressure in summer than in other seasons would be associated with target organ damage and if the associations would be different between summer and other seasons. Design and method: In 1054 untreated patients referred for ambulatory blood pressure monitoring, we performed measurements of urinary albumin-to-creatinine ratio (ACR, n = 1044), carotid-femoral pulse wave velocity (cfPWV, n = 1020) and left ventricular mass index (LVMI, n = 622). We investigated seasonality in nighttime blood pressure in our untreated outpatient sample and then its associations with various measures of target organ damage in comparison with those in other seasons. Results: Patients referred in spring (n = 337, 32.0%), summer (n = 210, 19.9%), autumn (n = 196, 18.6%) and winter (n = 311, 29.5%) had similar 24-h ambulatory systolic/diastolic blood pressure (P>0.25). However, both before and after adjustment for confounding factors, nighttime systolic/diastolic blood pressure differed significantly between seasons (P<0.001), being highest in summer and lowest in winter (adjusted mean values 117.0/75.3 mm Hg vs. 111.4/71.1 mm Hg). After adjustment for confounding factors, nighttime systolic/diastolic blood pressure were significantly and positively associated with ACR, cfPWV and LVMI (P<0.006). In season-specific analyses, statistical significance was reached for all the associations of nighttime blood pressure with target organ damage in summer (P<0.02), and for some of the associations in spring, autumn and winter. The association between nighttime systolic blood pressure and ACR was significantly stronger in patients examined in summer than those in winter (standardized beta, 0.31 vs 0.11 mg/mmol, P for interaction = 0.03). Conclusions: There is indeed seasonality in nighttime blood pressure level, as well as in its association with renal injury in terms of urinary albumin excretion.