Inverse correlation between daily outdoor temperature and blood pressure in six US cities

This study aims to evaluate the relationship between mean outdoor temperature and mean daily blood pressure (BP) and heart rate (HR) among six, large, geographically and climatically diverse US cities. We collected BP and HR data from Higi stations, located in a wide range of neighborhood grocery stores and retail pharmacies, from six US cities (Houston, Los Angeles, Miami, Boise, Chicago, and New York City). Outdoor daily temperature data were collected from the National Centers for Environmental Information's database. Pearson's correlation was used to assess the linear relationship between mean daily outdoor temperature and mean daily BP and HR for each city from May 2016 through April 2017. A total of 2 140 626 BP and HR readings were recorded in the six study cities. Mean outdoor temperature was inversely correlated with both mean daily average systolic (r=-0.69, P<0.0001) and diastolic (r=-0.71; P<0.0001) BPs, but not HR (r<0.0001, P=0.48). We also found that temperature change had a larger impact on BP in equatorial climates such as Miami compared with colder and more temperature variable cities like Chicago and Boise. Previous studies have found that BP varies seasonally, but few have looked at the impact of daily temperature on both BP and HR changes. Our study is one of the largest and most climatically diverse populations ever looking at this relationship. Our results suggest that temperature, and perhaps geography, should play a role in tailoring individualized evaluation and treatment for hypertensive diseases.