Trainer Sean Preuss has a new post on the issue. Well worth a read. For example:
The nine studies analyzed included 341 people between the ages of 20 and 72 years old. The studies ranged from six to 26 weeks long. The average blood pressure reduction was 3.2/3.5 mmHg.
Those reductions have value but are not life-altering. However, these studies were mostly performed with healthy people with desired blood pressure numbers. In general, people with less room to improve will do just that: improve to a smaller degree. Men and women with hypertension are likely to see greater improvements.