Seasonal blood pressure variation assessed by different measurement methods: systematic review and meta-analysis

Objective: The current study reviewed the published evidence on the seasonal changes in blood pressure (BP) assessed using different measurement methods. Methods: A systematic PubMed/EMBASE search was performed for studies assessing seasonal BP changes. Prospective and cross-sectional studies were included fulfilling the following criteria: (i) report of ambulatory and/or home BP data; (ii) cross-sectional studies reporting only office BP measurements and including 1000 or more participants. Results: Forty-seven studies fulfilled the selection criteria and were included (856 539 participants, weighted age 49.7 +/- 4.8 years, 38.8% treated hypertensive patients). The pooled summer minus winter SBP/DBP difference (95% confidence intervals) was office BP (29 studies) -5.6 (-7.1, -4.0)/-3.3 (-4.0, -2.7) mmHg; daytime ambulatory BP (15 studies) -3.4 (-4.4, -2.4)/-2.1 (-2.8, -1.4) mmHg; night-time ambulatory BP (13 studies) 1.3 (0.2, 2.3)/0.5 (-0.2, 1.2) mmHg; home BP (9 studies) -6.1 (-7.0, -5.1)/-3.1 (-3.5, -2.6) mmHg. Meta-analysis of 28 prospective studies (N = 5278) which examined the same individuals during different seasons showed pooled seasonal SBP/DBP difference: office BP -5.8/-4.0mmHg; daytime ambulatory BP -3.9/-2.7mmHg; night-time ambulatory BP 0.5/-0.5mmHg; home BP -6.4/-3.3mmHg. In meta-regression analysis seasonal systolic daytime ambulatory BP difference was related to the percentage of treated hypertensive patients across studies (P = 0.02) and borderline to age (P = 0.07). Conclusion: Seasonal BP changes are evident using all daytime BP measurement methods, but not with night-time ambulatory BP. The average BP decline in hot season is at about 5/3 (SBP/DBP) mmHg and appears to be larger in treated hypertensive patients and in older individuals.