hat free radicals are implicated in the aetiology of hypertension is evidenced by the beneficial effects of increased dietary antioxidants on blood pressure. The exact reason why antioxidants are beneficial at reducing blood pressure is not known, but may relate to the ability of free radicals to interfere with the production of nitric oxide in the endothelium of blood vessels. Because nitric oxide is required to cause blood vessel dilation, free radical induced decreases in production may result in elevations in arterial blood pressure, something that has been evidenced in the literature. In addition, hypertension involves activation of the sympathetic nervous system, and some evidence suggests that free radicals are involved in the enhanced sympathetic outflow. Heart failure is characterised by increased sympathetic nervous activity and antioxidants can acutely restore vagal nerve control, suggesting a free radical induced mechanisms of action.
Researchers have investigated the effects of vitamin C on hypertension by infusing 32 hypertensive patients and 20 normotensive patients with 3 grams of ascorbic acid over 5 min. The researchers then evaluated the effects of the vitamin C on blood pressure, heart rate and sympathetic nervous activity, when compared to a vehicle control. The results showed that the infusion of vitamin C significantly lowered the blood pressure of the hypertensive subjects but not the normotensive subjects, compared to the vehicle control. The fall in systolic blood pressure was reported as -4.9 mm Hg and the fall in diastolic blood pressure -0.7 mm Hg. The decrease in blood pressure was accompanied by a reduction in the sympathetic nervous activity in cardiac muscle in the hypertensive patients, but not the normotensive patients. The vitamin C infusion also restored vagal sympathetic activity and baroflex sensitivity in hypertensive subjects.
These results therefore support previous findings to show that vitamin C is beneficial at reducing blood pressure in subjects with hypertension (here). The mechanisms for this effect is not known, but the data presented in this study suggest it may involve modulation of sympathetic nervous system activity. The vitamin C was infused in this study, but other studies have used oral vitamin C to favourably affect blood pressure. Vitamin C intakes show an inverse association with cardiovascular disease, and this may relate to the effect of the vitamin on blood pressure, at least in part. Denham Harman conceived the free radical theory of disease and ageing in the 1950’s and since this time a number of diseases have confirmed to be caused at least in part by the action of free radicals. The aetiology of hypertension may also involve free radicals, explaining the benefit of plant based diets in reducing chronic blood pressure elevation.
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