S I Jaja1, S I Ogungbemi, M O Kehinde. 1. Dept. of Physiology, College of Medicine, University of Lagos PMB 12003, Lagos. Nigeria.
Abstract
INTRODUCTION: 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. AIM: 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. METHODOLOGY: 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. RESULTS: 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). CONCLUSION: 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.
INTRODUCTION: Studies have shown that oral, chronic, low dose vitamin C reduces blood pressure and forearm blood flow in normal young adults or hypertensivepatients. It is not clear how vitamin C affects cardiac function or autonomic control of blood pressure in young apparently healthy adults. AIM: 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. METHODOLOGY: 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. RESULTS: 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). CONCLUSION: 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.