Figure 1.

Seasonal, racial and geographical variation in blood pressure. A, Dots are monthly averages, lines are smoothing spline estimates, and shaded areas are 95% CI. Systolic blood pressure shows seasonal variation and is consistently higher in black than white patients. B through F, States with study centers and race‐specific SBP averages per state in winter and summer across the United States are shown. States with insufficient data (<10 patients or <2 months of observations) are shown in white. Mean annual SBP is highest in the “stroke belt” states (B). SBP is higher in winter (C and D) than summer (E and F) in all states. SBP is higher in black (C and E) than white (D and F) patients. SBP indicates systolic blood pressure.