This study is looking at whether vitamin C can help improve oxidative stress and blood vessel health in females after menopause. We will see if taking different amounts of vitamin C for a few days changes how the body handles stress from exercise. This could lead to safer ways to protect females from heart disease without using hormone therapy.
Cardiovascular disease (CVD) remains the leading cause of death in the United States. After menopause, females face a significantly increased risk of CVD due to declines in estrogen, which negatively impact nitric oxide (NO) production and vascular health. This coincides with an increase in reactive oxygen species (ROS), leading to an imbalance in redox signaling that may blunt beneficial adaptations to exercise. Vitamin C (ascorbic acid) is a potent antioxidant that may restore redox balance and endothelial function. However, most studies have been conducted in males using high doses that may suppress beneficial ROS signaling. In contrast, this trial focuses on the dose-response effects of short-term vitamin C supplementation (200 mg, 500 mg, and 1000 mg/day for 3 days) on ROS/NO balance, both at rest and in response to acute exercise, in PMF versus age-matched males. The study includes 15 sedentary PMF and 15 sedentary age-matched males, ages 45 and older. Participants complete 5-6 total study visits: one baseline/screening visit and four intervention visits in a randomized crossover design. Each intervention visit consists of 3 days of supplementation followed by fasting blood draws, vascular testing, and a 200-kcal high-intensity exercise bout on a cycle ergometer.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
OTHER
Masking
QUADRUPLE
Enrollment
30
Subjects will be supplemented with the following vitamin C doses: 0mg, 200mg, 500mg, 1000mg.
Flow-Mediated Dilation (FMD%) - Brachial Artery Endothelial Function
Brachial artery endothelial function will be measured by flow-mediated dilation (FMD) in each participant 5x (at baseline and after 0mg (placebo) 200mg, 500mg, and 1000mg of vitamin C). Participants will be placed in a supine position with their left forearm slightly extended and supinated with legs straight. The brachial artery will be imaged using a high-resolution 7.5MHz linear array transducer at rest, during 5 minutes of forearm occlusion via cuff inflation (250mmHg), and continuously for 2 minutes post-occlusion; an EKG trigger will be used to capture images during end-diastole of the cardiac cycle.
Time frame: 5x: Baseline/un-supplemented; after 3-days of 200mg of vitamin C supplementation; after 3-days of 500mg of vitamin C supplementation; after 3-days of 1000mg of vitamin C supplementation; after 3-days of 0mg of vitamin C/placebo supplementation
Basal ROS Concentrations - plasma 8-Isoprostane (8-iso) and malondialdehyde (MDA)
A venous blood sample will be collected from a vein in the antecubital fossa. Plasma will be separated out and stored at -80C until concentrations of 8-Isoprostane (8-iso) and malondialdehyde (MDA) are measured via commerically available ELISA kits. ROS concentrations will be measured at 5x points: at baseline and after 0mg (placebo), 200mg, 500mg, and 1000mg of vitamin C
Time frame: baseline and after 0mg/placebo, 200mg, 500mg, and 1000mg dose of vitamin C for 3-days each
Resting ROS/NO Balance - plasma N-oxides (nitrite and nitrate)
Venous blood samples will be collected from an antecubital fossa vein. Plasma will be separated out and stored at -80C until analysis. Plasma N-oxides (nitrite and nitrate) will be evaluated from the plasma via ozone-based chemiluminescence using a Sievers NOA model 280i. The N-oxides will be compared with the basal ROS also measured to calculate a ROS/NO balance.
Time frame: Baseline and after 3-days of placebo, 200mg, 500mg, and 1000mg doses of vitamin C
Exercise-Induced ROS (plasma 8-Isoprostane (8-iso) and malondialdehyde (MDA)) and NO (plasma nitrate and nitrite)
This platform is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional.
An intravenous catheter will be placed into a vein in the antecubital fossa. Participants will complete 4 high-intensity exercise sessions (\~200kcals). Each exercise session will be after 3-days of vitamin C supplementation (0mg/placebo, 200mg, 500mg, and 1000mg). Blood will be collected immediately before, immediately after, 15-min after, and 30-min after exercise. Plasma will be separated out and used to evaluate the changes in ROS (plasma 8-Isoprostane (8-iso) and malondialdehyde (MDA)) and NO (plasma nitrate and nitrite) from baseline/rest.
Time frame: 16x points: 4 exercise session with blood will be collected immediately before, immediately after, 15-min after, and 30-min after exercise
Vitamin C
Blood samples will be collected to evaluate compliance. We will measure vitamin C concentrations after each supplementation phase.
Time frame: 5x points over 5-6 weeks: (1) baseline/unsupplemented and after 3-days of (2) 0mg/placebo, (3) 200mg, (4) 500mg, and (5) 1000mg of vitamin C supplementation
Oral Nitrate Reducing Capacity
Assessment of the oral microbiome's ability to reduce nitrate to nitrite. This will be measured through an unstimulated saliva sample and a rinse of a standard nitrate solution.
Time frame: 5x points over 5-6 weeks: (1) baseline/unsupplemented and after 3-days of (2) 0mg/placebo, (3) 200mg, (4) 500mg, and (5) 1000mg of vitamin C supplementation
Pulse Wave Analysis and Velocity
Brachial artery blood pressures will be obtained using a standard sphygmomanometer. Aortic blood pressures will be obtained using applanation tonometry (SphygmoCor version 8.0, AtCor Medical).
Time frame: 5x points over 5-6 weeks: (1) baseline/unsupplemented and after 3-days of (2) 0mg/placebo, (3) 200mg, (4) 500mg, and (5) 1000mg of vitamin C supplementation
Microvascular Function
Participants will remain in a supine position with their left or right forearm slight extended and supinated. The cuff used for FMD will remain in place and two circular discs will be placed on the participants extended forearm. A laser Doppler imager (Moor Instruments - FLPI2) will be positioned directly over the participants forearm to measure skin blood flow in three different ways: microvascular flow mediated dilation, acetylcholine, and local thermal heating.
Time frame: 5x points over 5-6 weeks: (1) baseline/unsupplemented and after 3-days of (2) 0mg/placebo, (3) 200mg, (4) 500mg, and (5) 1000mg of vitamin C supplementation
Exercise Capacity
Participants will exercise using an incremental cycle ergometer protocol with increasing power output until volitional exhaustion is reached. The power output will increase in 3-minute stages, where blood is collected before the start of exercise and at the end of each stage. The LT will be established by analyzing the blood lactate-power output relationship. VO2 peak will be defined as the highest one min value attained during the test.
Time frame: Baseline only
Tissue Perfusion (NIRS)
Tissue oxygenation will be captured noninvasively using non-invasive, near-infrared spectrometry (NIRS, PortaMon, Artinis Medical Systems B.V., The Netherlands) positioned on the gastrocnemius (calf) or vastus lateralis (quad) muscle during the VO2/LT test and during each Experimental Visit (HIE sessions).
Time frame: 5x points over 5-6 weeks: (1) baseline/unsupplemented and after 3-days of (2) 0mg/placebo, (3) 200mg, (4) 500mg, and (5) 1000mg of vitamin C supplementation
Central Hemodynamics (Physioflow)
: Measures of central hemodynamics (cardiac output, etc.) will be non-invasively captured throughout the VO2/LT test and during each Experimental Visit (HIE sessions). Using electrodes placed on the participant's body and the principles of signal morphology impedance cardiography PhysioFlow provides estimates of central cardiac measures at rest and during exercise non-invasively.
Time frame: 5x points over 5-6 weeks: (1) baseline/unsupplemented and after 3-days of (2) 0mg/placebo, (3) 200mg, (4) 500mg, and (5) 1000mg of vitamin C supplementation