In general, reductions are not as great for people with blood pressure in the normal range: A Belgian review of scores of studies found that for people with high blood pressure, average reductions from exercise were 6.9 mm Hg systolic and 4.9 mm Hg diastolic, and for participants who did not have high blood pressure, only 1.9 mm Hg and 1.6 mm Hg.
Age seems to matter. In one study, exercise did not reduce systolic blood pressure in older people -- ages 55 to 75 -- although it did reduce diastolic pressure. (Both readings are important.)
Get developments in medicine, nutrition and fitness delivered to your inbox with our The Health Report newsletter. Sign up »
A possible reason: Systolic blood pressure increases as arteries grow stiffer, which happens as people age, and exercise did not reduce artery stiffness in the study participants.
Most studies about the effects of exercise have looked at aerobic exercise, although resistance training may also be effective. Recommendations call for exercising every day (or at least most days) for 30 to 45 minutes. Moderate exercise may be as effective, and possibly more so, than higher-intensity exercise.
Blood pressure can drop in just a few weeks of regular exercise. It can also pop right back up if you stop exercising.
During the exercise itself, it's normal for blood pressure to rise. But some people who have normal or only slightly raised blood pressure can experience abnormal spikes during exercise that may be a sign of high blood pressure to come. Such spikes are more likely to occur in those whose blood vessels are too stiff to expand to accommodate the increased blood flow that accompanies exercise -- a sign of early artery disease.
Just why exercise lowers blood pressure isn't clear, but there are several possibilities. Exercise makes the heart stronger, so it doesn't have to pump as hard, which in turn lowers the force on your arteries. Exercise reduces blood insulin levels, and high blood insulin has been linked to hypertension.
And regular exercise reduces blood levels of the hormone adrenaline. That, in turn, lowers blood pressure and heart rate.
You should consult your doctor before beginning an exercise program, especially if you already have high blood pressure.