The Journal of American Medical Association recently published a study that appears to support what I have also seen with my own blood pressure since adopting a plant-based diet. Unfortunately I am not able to read the entire article($140 for a subscription), but I have enough personal proof that this is true.
I have dealt with high blood pressure for most of my adult life. Switching to a plant-based was the biggest factor in seeing a difference in this. Regular exercise is just icing on the cake.
JAMA Network | JAMA Internal Medicine | Vegetarian Diets and Blood Pressure: A Meta-analysis.