A study of almost 50,000 Americans has found that "brisk walking" to be just as effective as running for reducing known risk factors for heart disease like high blood pressure and high cholesterol. However, this only holds true if the expended energy is the same between the runners and the walkers. Remember, in the same amount of time, runners run further and expend more energy than walkers. Therefore, if you chose walking over running, understand that you will need to exercise for longer than if you went for a run to get the equivalent health benefit.
IMPORTANTLY: Irrespective of the type of exercise, the more people exercised, the better their health.