How does exercise lower blood pressure?

Expert groups such as the American College of Cardiology and American Heart Association (ACC/AHA) Task Force on Clinical Practice Guidelines and the World Health Organization (WHO) recommend regular exercise to prevent and treat hypertension.^1,2 The blood pressure reduction may vary depending on the type of exercise.³ There are several proposed mechanisms for the effect of exercise on blood pressure, and some studies propose that these mechanisms are not mutually exclusive and work simultaneously to collectively lower blood pressure.^4-7 A meta-analysis of 72 trials on the effects of aerobic endurance training on blood pressure showed greater net reductions in hypertensive patients who completed training than others (p<0.001).⁵ Investigators attributed this improvement to decreases in plasma norepinephrine, renin activity, insulin resistance, body fat, and abdominal visceral fat. Because blood pressure is controlled by many different mechanisms, it is likely that the effects of exercise on blood pressure involve multiple of these same mechanisms.^8,9

Being overweight or obese has long been found to be associated with hypertension.¹ Exercise has been shown to reduce blood pressure by reducing overall weight.¹⁰ A meta-analysis of 25 randomized controlled trials demonstrated the effects of physical activity on weight loss and blood pressure.¹⁰ Results showed that both hypertensive and non-hypertensive subjects (n=4,874) lost weight and reduced systolic and diastolic blood pressure. There was an overall reduction of 1.05 mm Hg and 0.92 mm Hg in mean systolic and diastolic blood pressure, respectively per kilogram of weight loss (p<0.05).¹⁰ The average reduction of blood pressure in study participants was 4.78/3.56 mm Hg (systolic/diastolic) (p<0.05).¹⁰

Specifically, reducing visceral adipose tissue (VAT) from exercise has been shown to reduce blood pressure.¹¹ Visceral adipose tissue is fat found in the internal abdominal organs.¹² Some studies report that a higher amount of VAT, rather than weight, is associated with increased risk of high blood pressure.^12-14 In a study of 43 overweight men, VAT was significantly correlated with both baseline systolic blood pressure (r=.336, p<0.05) and diastolic blood pressure (r=.425, p<0.001).¹¹ Twenty-three of these men were enrolled in a daily exercise program for ten months. Mean VAT decreased from 108.7 cm² at baseline to 85.9 cm² after 10 months (p<0.01). Of the 12 hypertensive participants at baseline, eight were no longer hypertensive after the exercise intervention. Researchers concluded that decrease in VAT was the only anthropometric measurement that correlated with the decrease in blood pressure (r=0.477, p<0.05).

Another possible mechanism by which exercise lowers blood pressure is through increasing urinary sodium excretion.^7,15,16 Kiyonaga et al. studied blood pressure and sodium excretion in 12 patients with essential hypertension (WHO stages I-II).⁷ All medications were discontinued for a six-week control period before introducing exercise therapy for 10 or 20 weeks. Mean baseline blood pressure of 153/103 mm Hg was lowered to 139/94 and 136/90 mm Hg after 10 and 20 weeks of exercise therapy respectively (p<0.01). There was a corresponding increase in mean 24-hour urinary sodium excretion from 127.0 to 171.7 mEq/day in nine of the 12 patients after 10 weeks of exercise therapy (p<0.05). This suggests that the decrease in blood pressure was a result of the increased sodium excretion. Animal studies have also shown that exercise increases natriuresis and decreases systolic blood pressure.^15,16 However, other studies of human participants suggest that exercise does not cause significant changes in urinary sodium excretion.^6,17,18

Exercise has been shown to change the salt-sensitivity (SS) of blood pressure, which is a measure of blood pressure response to sodium intake.^19-21 Those who experience large increases in blood pressure in response to increased sodium intake are categorized as salt-sensitive, whereas those who produce minimal or no increase in blood pressure are categorized as salt-resistant.¹⁹ After conducting cross-sectional and longitudinal studies, researchers attribute the widely observed age-related increase of blood pressure to SS.^22,23 It has also been observed that patients who are salt-sensitive experience greater systolic and diastolic blood pressure increases over time than patients who are salt-resistant.²² One study demonstrated that exercise changed the SS status of hypertensive participants (n=31) from salt-sensitive to salt-resistant and lowered mean blood pressure.²⁰ At baseline, 20 participants were salt-sensitive and 11 participants were salt-resistant. After 6 months of exercise training, 12 participants were salt-sensitive and 19 were salt-resistant. Mean systolic blood pressure decreased from 152 to 145 mm Hg (p=0.037) and diastolic blood pressure decreased from 88 to 84 mm Hg (p=0.082). This suggests that not only does exercise lower blood pressure in the short-term, but exercise may also help prevent age-related increases of blood pressure due to salt-sensitivity.  

Exercise may also play a role in inducing neurohormonal changes to lower blood pressure.²⁴ Evidence suggest that hypertension may be related to elevated sympathetic nervous system activity, which mediates the release of norepinephrine to cause vasoconstriction and an increase in blood pressure.^25-28 Although there is a lack of significant data to support the reduction of sympathetic nerve activity and blood pressure after exercise, many studies have shown that exercise reduces plasma norepinephrine (NE) and lowers blood pressure.^18,29-31 Nelson et al. found that exercise training (seven times a week for a month) lowered plasma NE from 329 pg/ml at baseline to 220 pg/ml (p<0.01) in 13 hypertensive patients.³¹ Mean supine blood pressure also decreased from 143/96 mm Hg at baseline to 127/85 mm Hg (p<0.01).

Research suggests that exercise lowers insulin resistance in parallel with blood pressure.^5,6,32 Patients who have a subnormal response (plasma glucose) to a given concentration of insulin have a condition called insulin resistance.³³ Although much research has been done to find the exact relationship between hypertension and insulin resistance, the evidence is not definitive.³⁴ What is clear is that the presence of insulin resistance seems to increase the risk of incident hypertension and has also been shown to be more prevalent in hypertensive patients.^35-37 In the search for a more comprehensive relationship, exercise has been found to improve insulin sensitivity and decrease blood pressure.^5,6,32 One study compared the effects of aerobic exercise on insulin sensitivity and blood pressure in hypertensive participants (n=9) and normotensive controls (n=8).³² Improvement in insulin sensitivity was measured by the increase of glucose infusion rate (GIR) whereby an increase in GIR indicated an increase in insulin sensitivity. After six months of exercise, the mean GIR in the hypertensive group increased from 10.9 µmol • kg_FFM^-1 • min^-1 to 15 µmol • kg_FFM^-1 • min^-1 (p<0.01), although the GIR was still lower than the control group (24.2 µmol • kg_FFM^-1 • min^-1). After 6 months of exercise, mean blood pressure in the hypertensive group decreased from 147/93 mm Hg to 133/82 mm Hg (p= 0.003). The uncertainty of this mechanism is demonstrated by other animal and human studies that show no changes in blood pressure from exercise even after improving insulin sensitivity.^38,39

^References

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