No relevant seasonal influences on office and ambulatory blood pressure: data from a study in borderline hypertensive primary care patients.

Our objective was to study seasonal influences on office and ambulatory blood pressure. We therefore designed a prospective 7-month study of 47 borderline hypertensive patients in a primary care setting. We used no interventions. Our main outcome measures were the differences between summer and winter office and ambulatory blood pressures and 95% confidence intervals. Results showed that winter minus summer differences ranged from 0 to 3 mm Hg. Only one significant difference was found: ambulatory systolic daytime pressure was significantly higher (3 mm Hg) in winter than in summer. Our results do not confirm the data of earlier studies in hypertensives. In view of the small and clinically irrelevant winter-summer differences, it seems unnecessary to modify antihypertensive treatment of borderline hypertensives according to the season.