Electrocardiographic and blood pressure changes in apparently health male subjects following oral, chronic, low-dose vitamin c supplementation and /or change in posture

Abstract

Studies have shown that oral, chronic, low dose vitamin C reduces blood pressure and forearm blood flow in normal young adults or hypertensive patients. It is not clear how vitamin C affects cardiac function or autonomic control of blood pressure in young apparently healthy adults. This study was undertaken to examine the effects of a chronic, low dose (300 mg/day for 6 weeks) vitamin C supplementation on the electrocardiogram and autonomic control of blood pressure in apparently healthy male subjects. Electrocardiographic (ECG) and arterial blood pressure (BP) changes were assessed following change in posture with or without oral, chronic low dose vitamin C supplementation in twenty (20) apparently healthy male subjects (mean age 28.2 +/- 2.0 yrs). Blood pressure (BP, mm Hg) and ECG measurements (amplitude, mV; duration or interval, ms) were recorded in the supine position and immediately on assumption of the upright position. Heart rate (HR; beats/min) was calculated from the ECG while rate pressure product (RPP; arbitrary units) was calculated and used as a measure of myocardial oxygen demand. Each subject was then placed on oral vitamin C at a dose of 300 mg/day for 6 weeks. Measurements were made again after the period. Change in posture caused significant reductions in P-wave amplitude, QRS amplitude and duration, T-wave amplitude and systolic blood pressure (SBP), diastolic blood pressure (DBP), and mean arterial blood pressure (MABP) (p < 0.01 respectively). PR and RR intervals also fell (p < 0.05 and p < 0.001 respectively) while HR and RPP increased (p < 0.001) Vitamin C decreased T-wave amplitude (p < 0.01) and QRS duration (p < 0.01). Also, SBP, DBP, MABP and RPP fell (p < 0.01 in each case). After vitamin C supplement ation, change in posture decreased P-wave amplitude, T-wave duration, P-wave duration, QT interval and RR interval (p < 0.05 respectively). BP and HR responses to postural change were attenuated by vitamin C supplementation. SBP fell by 7.4 +/- 1.0 mm Hg (Vs 12.2 +/-0.1 mm Hg pre-supplementation), DBP by 5.4 +/- 0.6 mm Hg (Vs 10.4 +/- 0.1 mm Hg pre-supplementation) and MABP by 6.1 +/- 1.4 mm Hg (Vs 11.0 +/- 0.1 mm Hg pre-supplementation). HR increased by 18.6 +/- 1.0 beats/min (Vs 29.6 +/- 2.5 beats/min pre-supplementation) and RPP by 1385.6 +/- 126.4 units (Vs 2370.0 +/- 105.6 units pre-supplementation). Chronic, low dose vitamin C supplementation enhanced cardiovascular autonomic activity in apparently healthy young subjects. It minimized the fluctuations in BP and HR and also reduced myocardial oxygen demand following postural change.