Plasma ascorbic acid concentrations relate inversely to blood pressure in human subjects

Preoperative and postoperative administration of vitamin C in cardiac surgery patients - settings, dosages, duration, and clinical outcomes: a narrative review

Vitamin C or ascorbic acid is a water-soluble vitamin capable of directly donating electrons to reactive oxygen species, attenuating electrical remodeling, and cardiac dysfunction in patients undergoing cardiac surgery (CS), considered one of the most effective defenses against free radicals in the blood, thus being one of the first antioxidants consumed during oxidative stress. The aim of this review is to assess the effects of perioperative administration of vitamin C in CS patients. A comprehensive literature search was conducted in order to identify prospective cohort studies and/or randomized controlled trials reporting on the perioperative effects of vitamin C among adult patients undergoing CS. Studies published between January 1980 to December 2022 were included in our search, resulting in a total of 31 articles that met all our inclusion criteria. There seems to be a beneficial effect of vitamin C supplementation in arrhythmias such as in postoperative atrial fibrillation, reduction of ICU length of stay, and hospital length of stay, reduction in postoperative ventilation time, in inotropic demand, and in postoperative fatigue. Vitamin C can act as a scavenger of free radicals to decrease the peroxidation of the lipids present in the cell membrane, and to protect the myocardium postoperatively from ischemia/reperfusion injury, thus attenuating oxidative stress and inflammation. It represents a readily available and cost-effective strategy that could improve the outcome of patients undergoing CS, by reducing the risk of serious cardiovascular adverse events, both perioperatively and postoperatively.

Differential influences of serum vitamin C on blood pressure based on age and sex in normotensive individuals

Aim

Hypertension is among the most prevalent chronic diseases with diverse etiology, affecting over 1 billion people globally. In numerous studies, vitamin C inversely correlated with blood pressure and was suspected to have antihypertensive properties. Currently, there is conflicting evidence regarding the relationship between vitamin C and blood pressure, with most studies being conducted on hypertensive subjects. The principal objective of this project was to investigate the relationship between vitamin C and blood pressure in normotensive adult subjects.

Methods

A total of 2,533 individuals aged 20 years and above were enrolled in the present study from the National Health and Nutrition Examination Survey (NHANES) 2017-2018. Outcome variables were systolic blood pressure (SBP) and diastolic blood pressure (DBP). Serum vitamin C was regarded as an independent variable. EmpowerStats software and R (version 3.4.3) were used to examine the association between vitamin C and SBP or DBP.

Results

Vitamin C was reversely correlated with both SBP (β = −0.02, 95% CI: −0.03 to −0.00, p = 0.0306) and DBP (β = −0.02, 95% CI: −0.04 to −0.01, p = <0.0011) after adjusting all covariates. This reverse relationship may be affected by a number of factors, including a person’s gender, age, race, and ethnicity. A U-shaped association between vitamin C and SBP in females and an inverted one between vitamin C and DBP in males were detected, respectively. We further calculated the inflection points at 90.3 μmol/L for females and 40 μmol/L for males. It is somewhat surprising that a reverse U-shaped distribution between vitamin C and SBP and DBP in people over 50 was detected, and the point of inflection of vitamin C were all located at 40 μmol/L.

Conclusion

Vitamin C was negatively correlated with both SBP and DBP in this cross-sectional analysis. However, a U-shaped relationship and an inverted one were also observed in certain people, which implied that, though vitamin C is considered a vital antioxidant, maintaining vitamin C at appropriate levels may be beneficial according to different populations.

Vitamin C Lowers Blood Pressure in Spontaneously Hypertensive Rats by Targeting Angiotensin-Converting Enzyme I Production in a Frequency-Dependent Manner

The lowering blood pressure effect of vitamin C (VC) has been evaluated in various models. As VC has a fast degradation rate in the body after consumption, a study of the frequency-dependent manner of VC is essential for the sustained antihypertension effect of VC. In this study, we investigated the frequency and dose dependency of vitamin C (VC) on blood pressure reduction in spontaneously hypertensive rats (SHRs). Wistar–Kyoto rats (WKYs) and SHRs were orally administered tap water or VC (250, 500, 1000, and 2000 mg/60 kg/day). Blood pressures were measured using the tail-cuff method, and thoracic aortas, liver, and blood were harvested from sacrificed rats after 8 weeks to measure angiotensinogen, angiotensin-converting enzyme (ACE) I, endothelial nitric oxide synthase (eNOS), and total nitric oxide (NOx) concentration. VC decreased blood pressure from the fourth week with no significant differences between doses. The twice-a-day administration of VC decreased blood pressure from the second week, and the blood pressure in these groups was close to that of the WKY group in the eighth week. Treatment with once a day VC decreased ACE I production which was further significantly reduced in twice a day groups. Angiotensinogen and eNOS production were increased upon VC treatment but were not significant among groups. The NOx content was decreased by VC treatment. These results suggest that VC lowers blood pressure in SHRs by directly targeting ACE I production in a frequency-dependent manner and may improve endothelial function depending on the frequency of administration.

Vitamin C and Cardiovascular Disease: An Update

The potential beneficial effects of the antioxidant properties of vitamin C have been investigated in a number of pathological conditions. In this review, we assess both clinical and preclinical studies evaluating the role of vitamin C in cardiac and vascular disorders, including coronary heart disease, heart failure, hypertension, and cerebrovascular diseases. Pitfalls and controversies in investigations on vitamin C and cardiovascular disorders are also discussed.

Association between Serum Vitamin C and the Blood Pressure: A Systematic Review and Meta-Analysis of Observational Studies

Background

Hypertension is regarded as a major and independent risk factor of cardiovascular diseases, and numerous studies observed an inverse correlation between vitamin C intake and blood pressure.

Aim

Our aim is to investigate the relationship between serum vitamin C and blood pressure, including the concentration differences and the correlation strength.

Method

Two independent researchers searched and screened articles from the National Library of Medicine, Cochrane Library, Web of Science, China National Knowledge Infrastructure, VIP databases, and WANFANG databases. A total of 18 eligible studies were analyzed in the Reviewer Manager 5.3 software, including 14 English articles and 4 Chinese articles.

Results

In the evaluation of serum vitamin C levels, the concentration in hypertensive subjects is 15.13 μmol/L lower than the normotensive ones (mean difference = −15.13, 95% CI [-24.19, -6.06], and P = 0.001). Serum vitamin C has a significant inverse relation with both systolic blood pressure (Fisher′s Z = −0.17, 95% CI [-0.20, -0.15], P < 0.00001) and diastolic blood pressure (Fisher′s Z = −0.15, 95% CI [-0.20, -0.10], P < 0.00001).

Conclusions

People with hypertension have a relatively low serum vitamin C, and vitamin C is inversely associated with both systolic blood pressure and diastolic blood pressure.

Effects of α-tocopherol on bone marrow mesenchymal cells derived from type II diabetes mellitus rats

It is widely accepted that vitamin E (VE) acts as an antioxidant and is involved in various metabolic systems including the regulation of gene expression and inhibition of cell proliferation. The most predominant isoform of VE in the living body is α-tocopherol. However, the influence of α-tocopherol on bone marrow mesenchymal cells (BMMCs) in a background of type II diabetes mellitus (DM) has not been investigated. The focus of the present study was to clarify the effect of α-tocopherol on BMMCs derived from rats with type II DM and the underlying mechanisms involved. BMMCs were isolated from rats with type II DM. The BMMCs were either untreated or exposed to α-tocopherol at concentrations of 1.0, 10, and 100 μM, and the resulting effects of α-tocopherol on cell proliferation, H₂O₂ activity, and antioxidant and inflammatory cytokine production were examined. At 100 μM, α-tocopherol had no effect on cell proliferation, but H₂O₂ activity was significantly increased. At 10 μM, α-tocopherol increased the gene expression of IL-1β, and markedly promoted that of TNF-α. Expression of catalase in the presence of 100 μM α-tocopherol was lower than for the other concentrations. At a low concentration, α-tocopherol exerted good antioxidant and anti-inflammatory effects on BMMCs. The study suggests that maintaining α-tocopherol at a low concentration might promote the recovery of BMMCs from oxidative stress.

Vitamin C supplementation for the primary prevention of cardiovascular disease

BACKGROUND

Vitamin C is an essential micronutrient and powerful antioxidant. Observational studies have shown an inverse relationship between vitamin C intake and major cardiovascular events and cardiovascular disease (CVD) risk factors. Results from clinical trials are less consistent.

OBJECTIVES

To determine the effectiveness of vitamin C supplementation as a single supplement for the primary prevention of CVD.

SEARCH METHODS

We searched the following electronic databases on 11 May 2016: the Cochrane Central Register of Controlled Trials (CENTRAL) in the Cochrane Library; MEDLINE (Ovid); Embase Classic and Embase (Ovid); Web of Science Core Collection (Thomson Reuters); Database of Abstracts of Reviews of Effects (DARE); Health Technology Assessment Database and Health Economics Evaluations Database in the Cochrane Library. We searched trial registers on 13 April 2016 and reference lists of reviews for further studies. We applied no language restrictions.

SELECTION CRITERIA

Randomised controlled trials of vitamin C supplementation as a single nutrient supplement lasting at least three months and involving healthy adults or adults at moderate and high risk of CVD were included. The comparison group was no intervention or placebo. The outcomes of interest were CVD clinical events and CVD risk factors.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected trials for inclusion, abstracted the data and assessed the risk of bias.

MAIN RESULTS

We included eight trials with 15,445 participants randomised. The largest trial with 14,641 participants provided data on our primary outcomes. Seven trials reported on CVD risk factors. Three of the eight trials were regarded at high risk of bias for either reporting or attrition bias, most of the 'Risk of bias' domains for the remaining trials were judged as unclear, with the exception of the largest trial where most domains were judged to be at low risk of bias.The composite endpoint, major CVD events was not different between the vitamin C and placebo group (hazard ratio (HR) 0.99, 95% confidence interval (CI) 0.89 to 1.10; 1 study; 14,641 participants; low-quality evidence) in the Physicians Health Study II over eight years of follow-up. Similar results were obtained for all-cause mortality HR 1.07, 95% CI 0.97 to 1.18; 1 study; 14,641 participants; very low-quality evidence, total myocardial infarction (MI) (fatal and non-fatal) HR 1.04 (95% CI 0.87 to 1.24); 1 study; 14,641 participants; low-quality evidence, total stroke (fatal and non-fatal) HR 0.89 (95% CI 0.74 to 1.07); 1 study; 14,641 participants; low-quality evidence, CVD mortality HR 1.02 (95% 0.85 to 1.22); 1 study; 14,641 participants; very low-quality evidence, self-reported coronary artery bypass grafting (CABG)/percutaneous transluminal coronary angioplasty (PTCA) HR 0.96 (95% CI 0.86 to 1.07); 1 study; 14,641 participants; low-quality evidence, self-reported angina HR 0.93 (95% CI 0.84 to 1.03); 1 study; 14,641 participants; low-quality evidence.The evidence for the majority of primary outcomes was downgraded (low quality) because of indirectness and imprecision. For all-cause mortality and CVD mortality, the evidence was very low because more factors affected the directness of the evidence and because of inconsistency.Four studies did not state sources of funding, two studies declared non-commercial funding and two studies declared both commercial and non-commercial funding.

AUTHORS' CONCLUSIONS

Currently, there is no evidence to suggest that vitamin C supplementation reduces the risk of CVD in healthy participants and those at increased risk of CVD, but current evidence is limited to one trial of middle-aged and older male physicians from the USA. There is limited low- and very low-quality evidence currently on the effect of vitamin C supplementation and risk of CVD risk factors.

The Paraoxonase 1 Arylesterase Activity, Total Oxidative Stress, Nitric Oxide and Vitamin C Levels in Maternal Serum, and Their Relation to Birth Weight of Newborn

AIM

Aim of this study is to find out clinical relevance of estimating PON1 arylesterase activity, total oxidative stress (TOS), nitric oxide (NO), and vitamin C levels in maternal serum for prediction of birth weight of newborn.

METHODS

We have investigated the PON1 arylesterase activity, TOS, NO, vitamin C, total protein, and albumin levels in 56 postnatal clinic patients having newborn weighing <2500 gm (low birth weight) and compared with 56 postnatal clinic patients having newborn weighing >2500 gm. Samples were collected immediately after delivery.

RESULTS

PON1 arylesterase activity levels show significant decrease in cases as compared to controls (93.27 ± 13.76 kU/l vs. 112.77 ± 9.42 kU/l). Nitric oxide (nitrate + nitrite) levels are also found to be significantly decreased in cases with respect to controls (22.89 ± 2.65 umol/l vs. 24.73 ± 3.80 umol/l). Total oxidative stress is significantly increased in cases than in control subjects (23.34 ± 2.64 μmol H2O2 equiv./l vs. ± 21.43 ± 2.47 μmol H2O2 equiv/l). Vitamin C levels are also significantly decreased in cases as compared to controls (1.23 ± 0.25 mg/dl vs. 1.34 ± 0.28 mg/dl). Positive correlation between neonatal birth weight and maternal serum PON1 arylesterase activity (r = 0.682, p < 0.05) while negative correlation is obtained between neonatal birth weight and maternal serum oxidative stress (r = -0.478, p < 0.05). Logistic regression analysis is applied for assessing predictive utility which demonstrated a significant association of birth weight with PON1 arylesterase activity (AUC = 0.960, Naglekerke's R (2) = 0.793, p < 0.05).

CONCLUSION

Decreased arylesterase activity and antioxidant vitamin C levels with increased total oxidative stress in maternal serum may be considered as the additional risk factors for the development of low birth weight newborn.

Ethnopharmacology, phytochemistry, and biological activities of Cymbopogon citratus (DC.) Stapf extracts

Cymbopogon citratus is a widely distributed perennial herb belonging to the Poaceae family and has been extensively consumed for its medicinal, cosmetic, and nutritional effects for centuries. A large number of reports have been published describing the pharmacological, biological, and therapeutic actions of this herb. In this review, we summarized the literatures on related studies (up to January, 2014) that highlighted the pharmacologic and biological effects of the major phytochemicals isolated from C. citratus extracts and its essential oil. The components of the essential oils found in C. citratus have a similar pharmacokinetic properties, including absorption, distribution, metabolism, and excretion. They are quickly absorbed following oral, pulmonary, and dermal administration. Based on the published reports, it can also be inferred that, after absorption from the small intestine, some phytochemicals in C. citratus can undergo oxidation, glucuronidation, sulfation, and/or O-methylation. Excretion is through urine, feces and/or expired volatiles. The biotransformation reactions of C. citratus bioactive constituents are essential for its relatively safe consumption and therapeutic applications. The data available so far warrant further studies evaluating C. citratus pharmacokinetics. Reliable pharmacokinetic data in humans would be critical for a better understanding of the the systemic handling of C. citratus.

Reactive oxygen species, vascular Noxs, and hypertension: focus on translational and clinical research

SIGNIFICANCE

Reactive oxygen species (ROS) are signaling molecules that are important in physiological processes, including host defense, aging, and cellular homeostasis. Increased ROS bioavailability and altered redox signaling (oxidative stress) have been implicated in the onset and/or progression of chronic diseases, including hypertension.

RECENT ADVANCES

Although oxidative stress may not be the only cause of hypertension, it amplifies blood pressure elevation in the presence of other pro-hypertensive factors, such as salt loading, activation of the renin-angiotensin-aldosterone system, and sympathetic hyperactivity, at least in experimental models. A major source for ROS in the cardiovascular-renal system is a family of nicotinamide adenine dinucleotide phosphate oxidases (Noxs), including the prototypic Nox2-based Nox, and Nox family members: Nox1, Nox4, and Nox5.

CRITICAL ISSUES

Although extensive experimental data support a role for increased ROS levels and altered redox signaling in the pathogenesis of hypertension, the role in clinical hypertension is unclear, as a direct causative role of ROS in blood pressure elevation has yet to be demonstrated in humans. Nevertheless, what is becoming increasingly evident is that abnormal ROS regulation and aberrant signaling through redox-sensitive pathways are important in the pathophysiological processes which is associated with vascular injury and target-organ damage in hypertension.

FUTURE DIRECTIONS

There is a paucity of clinical information related to the mechanisms of oxidative stress and blood pressure elevation, and a few assays accurately measure ROS directly in patients. Such further ROS research is needed in humans and in the development of adequately validated analytical methods to accurately assess oxidative stress in the clinic.

Amperometric glucose biosensor based on electroconductive hydrogels

Fabrication of an enzyme amperometric biosensor for glucose via electropolymerization of pyrrole in the presence of glucose oxidase onto a hydrogel coated platinum electrode is hereby established as a viable biotransducer fabrication method. Platinum micro- (φ=25 μm) and macro- (φ=100 μm) electrodes were electrochemically activated and chemically modified with 3-aminopropyl-trimethoxysilane (APTMS), functionalized with acryloyl(polyethyleneglycol)-N-hydroxysuccinamide (ACRL-PEG-NHS), dipped into a polyHEMA based hydrogel cocktail and UV cross-linked. Electropolymerization of Py in the presence of GOx produced glucose responsive biotransducers that showed; (i) a 4-fold reduction in sensitivity compared with directly electropolymerized PPy films, (ii) an electropolymerization charge density dependence of biotransducer sensitivity and enzyme activity that was maximal at 1.0 mC/cm(2) with an apparent K(M) of 33 mM, (iii) interference screening of ascorbic acid and (iv) a temporal increase in sensitivity with storage over a 17 days period. This method has the ability to precisely and quantitatively add enzyme catalytic bioactivity to metal or semiconductor biointerfaces for applications in biosensors, bioelectronics and bionics.

Applying genomics to nutrition and lifestyle modification

Personalized nutrition aims to prevent the onset and development of chronic diseases by targeting dietary recommendations to an individual’s genetic profile. Gene–diet interactions that affect metabolic pathways relevant to disease risk are continuously being uncovered. Discoveries in the field of nutrigenomics demonstrate that some individuals may benefit from adhering to different dietary guidelines than others, depending on their genotype. Certain industries have already begun to capitalize on the anticipation that knowledge of genomic information could help prevent the risk of developing diseases. Although disclosure of genetic information has been associated with the adoption of positive health-related behaviors under certain circumstances, the effect of providing gene-based dietary advice on motivating adherence to favorable dietary changes is largely unknown.

Effects of vitamin C supplementation on blood pressure: a meta-analysis of randomized controlled trials

BACKGROUND

In observational studies, increased vitamin C intake, vitamin C supplementation, and higher blood concentrations of vitamin C are associated with lower blood pressure (BP). However, evidence for blood pressure-lowering effects of vitamin C in clinical trials is inconsistent.

OBJECTIVE

The objective was to conduct a systematic review and meta-analysis of clinical trials that examined the effects of vitamin C supplementation on BP.

DESIGN

We searched Medline, EMBASE, and Central databases from 1966 to 2011. Prespecified inclusion criteria were as follows: 1) use of a randomized controlled trial design; 2) trial reported effects on systolic BP (SBP) or diastolic BP (DBP) or both; 3) trial used oral vitamin C and concurrent control groups; and 4) trial had a minimum duration of 2 wk. BP effects were pooled by random-effects models, with trials weighted by inverse variance.

RESULTS

Twenty-nine trials met eligibility criteria for the primary analysis. The median dose was 500 mg/d, the median duration was 8 wk, and trial sizes ranged from 10 to 120 participants. The pooled changes in SBP and DBP were -3.84 mm Hg (95% CI: -5.29, -2.38 mm Hg; P < 0.01) and -1.48 mm Hg (95% CI: -2.86, -0.10 mm Hg; P = 0.04), respectively. In trials in hypertensive participants, corresponding reductions in SBP and DBP were -4.85 mm Hg (P < 0.01) and -1.67 mm Hg (P = 0.17). After the inclusion of 9 trials with imputed BP effects, BP effects were attenuated but remained significant.

CONCLUSIONS

In short-term trials, vitamin C supplementation reduced SBP and DBP. Long-term trials on the effects of vitamin C supplementation on BP and clinical events are needed.

Is vitamin C an effective antihypertensive supplement? A review and analysis of the literature

OBJECTIVE

Hypertension is a common condition with high mortality from associated diseases. Epidemiological evidence suggests that a dietary deficiency of vitamin C may be a risk factor for hypertension. However the literature on vitamin C interventional trials appears divided on the efficacy of vitamin C utilization clinically.

METHODS

A literature search and review of published trials using vitamin C in treating patients with hypertension was undertaken. Relevant references were located using MEDLINE (1966-2005) and the bibliographies of located articles.

RESULTS

Thirteen trials making up 14 separate groups were identified and analyzed providing a pooled population of 284 hypertensive patients (52% female), with a weighted mean age of 58.8 +/- 9.5 years. Median vitamin C dose and study intervention duration was 500mg/day and 6 weeks respectively. The weighted mean baseline and post treatment systolic blood pressures across all 14 groups were 149.6 +/- 11.1 and 145.7 +/- 11.0 mmHg respectively. This represented a systolic blood pressure decrease of 3.9 mmHg. Seven of the 14 groups ascertained statistically significant reductions (p < .05) in systolic blood pressures. However only 2 of the 14 groups found significant reductions in diastolic blood pressure. The weighted mean baseline and post treatment diastolic blood pressures across all 14 groups were 84.6 +/- 4.4 and 82.5 +/- 4.1 mmHg respectively. This represented a diastolic blood pressure decrease of 2.1 mmHg.

CONCLUSION

Vitamin C supplementation in hypertensive patients appears to possess modest effects on reducing systolic blood and diastolic blood pressure.

The Role of Antioxidant Vitamins in Cardiovascular Disease

Objective:

To review the current data on the role of antioxidant vitamins in cardiovascular disease.

Data Sources:

Articles were obtained from a MEDLINE search covering all years. Terms used in the search included combinations of antioxidant, vitamin, vitamin E, vitamin C, beta-carotene, and cardiovascular disease. Reference lists from articles were examined for additional references.

Study Selection and Data Extraction:

Randomized clinical trials were selected and evaluated for study design and data obtained. Observational studies, meta-analyses, and basic science articles were also reviewed for background.

Data Synthesis:

The use of dietary supplements, including vitamins, minerals, and herbal products, is common among patients in the US. Vitamin E, vitamin C, and beta-carotene are all supplements with reported antioxidant activity. Because oxidative stress has been implicated in the development of cardiovascular disease, there has been significant research at the basic science level as well as observational studies and randomized placebo-controlled trials examining the potential impact of vitamin E, vitamin C, and beta-carotene in the prevention and treatment of cardiovascular disease. While basic science data and data from observational studies have identified benefit from antioxidant vitamin supplementation, randomized clinical trials have failed to support a role for antioxidant vitamin supplementation in the prevention or treatment of cardiovascular disease.

Conclusions:

Data from randomized clinical trials do not support the use of antioxidant vitamins in cardiovascular disease. Therefore, antioxidant vitamins should not be recommended to patients for prevention or treatment of cardiovascular disease.

Dietary protein and blood pressure: a systematic review

BACKGROUND

Elevated blood pressure (BP), which is a major risk factor for cardiovascular disease, is highly prevalent worldwide. Recently, interest has grown in the role of dietary protein in human BP. We performed a systematic review of all published scientific literature on dietary protein, including protein from various sources, in relation to human BP.

METHODOLOGY/PRINCIPAL FINDINGS

We performed a MEDLINE search and a manual search to identify English language studies on the association between protein and blood pressure, published before June 2010. A total of 46 papers met the inclusion criteria. Most observational studies showed no association or an inverse association between total dietary protein and BP or incident hypertension. Results of biomarker studies and randomized controlled trials indicated a beneficial effect of protein on BP. This beneficial effect may be mainly driven by plant protein, according to results in observational studies. Data on protein from specific sources (e.g. from fish, dairy, grain, soy, and nut) were scarce. There was some evidence that BP in people with elevated BP and/or older age could be more sensitive to dietary protein.

CONCLUSIONS/SIGNIFICANCE

In conclusion, evidence suggests a small beneficial effect of protein on BP, especially for plant protein. A blood pressure lowering effect of protein may have important public health implications. However, this warrants further investigation in randomized controlled trials. Furthermore, more data are needed on protein from specific sources in relation to BP, and on the protein-BP relation in population subgroups.

Functional genetic variants of glutathione S-transferase protect against serum ascorbic acid deficiency

BACKGROUND

Glutathione S-transferases (GSTs) are detoxifying enzymes that contribute to the glutathione-ascorbic acid (vitamin C) antioxidant cycle.

OBJECTIVE

The objective was to determine whether GST genotypes modify the association between dietary vitamin C and serum ascorbic acid.

DESIGN

Nonsmoking men and women (n = 905) between 20 and 29 y of age were participants in the Toronto Nutrigenomics and Health Study. Overnight fasting blood samples were collected to determine serum ascorbic acid concentrations by HPLC and to genotype for deletion polymorphisms in GSTM1 and GSTT1 and an Ile105Val substitution in GSTP1. A 196-item food-frequency questionnaire was used to estimate vitamin C intake.

RESULTS

A gene-diet interaction on serum ascorbic acid was observed for GSTM1 (P = 0.04) and GSTT1 (P = 0.01) but not for GSTP1 (P = 0.83). The odds ratio (95% CI) for serum ascorbic acid deficiency (<11 micromol/L) was 3.20 (1.88, 5.44) for subjects who did not meet the Recommended Dietary Allowance of vitamin C compared with those who did. The corresponding odds ratios (95% CIs) were 2.17 (1.10, 4.28) and 12.28 (4.26, 33.42), respectively, for individuals with the GSTT1*1/*1 +*1/*0 (functional) and GSTT1*0/*0 (null) genotypes and 2.29 (0.96, 5.45) and 4.03 (2.01, 8.09), respectively, for the GSTM1*1/*1+GSTM1*1/*0 and GSTM1*0/*0 genotypes.

CONCLUSIONS

The recommended intake of vitamin C protects against serum ascorbic acid deficiency, regardless of genotype. Individuals with GST null genotypes had an increased risk of deficiency if they did not meet the Recommended Dietary Allowance for vitamin C, which suggests that the GST enzymes protect against serum ascorbic acid deficiency when dietary vitamin C is insufficient.

Vitamin C deficiency in a population of young Canadian adults

A cross-sectional study of the 979 nonsmoking women and men aged 20-29 years who participated in the Toronto Nutrigenomics and Health Study from 2004 to 2008 was conducted to determine the prevalence of serum ascorbic acid (vitamin C) deficiency and its association with markers of chronic disease in a population of young Canadian adults. High performance liquid chromatography was used to determine serum ascorbic acid concentrations from overnight fasting blood samples. A 1-month, 196-item food frequency questionnaire was used to assess dietary intakes. Results showed that 53% of subjects had adequate, 33% had suboptimal, and 14% had deficient levels of serum ascorbic acid. Subjects with deficiency had significantly higher measurements of mean C-reactive protein, waist circumference, body mass index, and blood pressure than did subjects with adequate levels of serum ascorbic acid. The odds ratio for serum ascorbic acid deficiency was 3.43 (95% confidence interval: 2.14, 5.50) for subjects who reported not meeting the recommended daily intake of vitamin C compared with those who did. Results suggest that 1 of 7 young adults has serum ascorbic acid deficiency, in part, because of unmet recommended dietary intakes. Furthermore, serum ascorbic acid deficiency is associated with elevated markers of chronic disease in this population of young adults, which may have long-term adverse health consequences.

Is the anti-hypertensive effect of dietary supplements via aldehydes reduction evidence based? A systematic review

Growing evidence indicates that insulin resistance and oxidative stress are involved in the pathogenesis of essential hypertension. In insulin-resistant states, like obesity and type 2 diabetes, altered glucose metabolism may lead to increased formation of methylglyoxal and other ketoaldehydes. Animal studies have shown that increased levels of endogenous aldehydes may lead to hypertension and oxidative stress. In animal models, the administration of vitamin C, vitamin B6 or alpha-lipoic acid reduced tissue levels of aldehydes, prevented oxidative stress, and lowered blood pressure. The purpose of this review article is to critically evaluate the available evidence for the role of dietary supplements in hypertension treatment.

Vitamin C in plasma is inversely related to blood pressure and change in blood pressure during the previous year in young Black and White women

Background

The prevalence of hypertension and its contribution to cardiovascular disease risk makes it imperative to identify factors that may help prevent this disorder. Extensive biological and biochemical data suggest that plasma ascorbic acid may be such a factor. In this study we examined the association between plasma ascorbic acid concentration and blood pressure (BP) in young-adult women.

Methods

Participants were 242 Black and White women aged 18–21 yr from the Richmond, CA, cohort of the National Heart, Lung and Blood Institute Growth and Health Study. We examined the associations of plasma ascorbic acid with BP at follow-up year 10, and with change in BP during the previous year.

Results

In cross-sectional analysis, plasma ascorbic acid at year 10 was inversely associated with systolic BP and diastolic BP after adjusting for race, body mass index, education, and dietary intake of fat and sodium. Persons in the highest one-fourth of the plasma ascorbic acid distribution had 4.66 mmHg lower systolic BP (95% CI 1.10 to 8.22 mmHg, p = 0.005) and 6.04 mmHg lower diastolic BP (95% CI 2.70 to 9.38 mmHg, p = 0.0002) than those in the lowest one-fourth of the distribution. In analysis of the change in BP, plasma ascorbic acid was also inversely associated with change in systolic BP and diastolic BP during the previous year. While diastolic blood pressure among persons in the lowest quartile of plasma ascorbic acid increased by 5.97 mmHg (95% CI 3.82 to 8.13 mmHg) from year 9 to year 10, those in the highest quartile of plasma vitamin C increased by only 0.23 mmHg (95% CI -1.90 to +2.36 mmHg) (test for linear trend: p < 0.0001). A similar effect was seen for change in systolic BP, p = 0.005.

Conclusion

Plasma ascorbic acid was found to be inversely associated with BP and change in BP during the prior year. The findings suggest the possibility that vitamin C may influence BP in healthy young adults. Since lower BP in young adulthood may lead to lower BP and decreased incidence of age-associated vascular events in older adults, further investigation of treatment effects of vitamin C on BP regulation in young adults is warranted.

Oxidative stress in prehypertension: rationale for antioxidant clinical trials

Prehypertension has been recently described as an independent category of blood pressure. Mounting evidence suggests that blood pressure in the prehypertensive range is associated with an increased risk of developing hypertension and cardiovascular disease. Several reports have assigned a critical role for oxidative stress in these disease processes. This review focuses on the clinical and experimental studies done in prehypertension and hypertension within the context of oxidative stress. This article also provides insights into why diverse therapeutic interventions, which have in common the ability to reduce oxidative stress, can impede or delay the onset of hypertension in prehypertension subjects.

Clinical pharmacology and therapeutic use of antioxidant vitamins

The clinical use of antioxidants has gained considerable interest during the last decade. It was suggested from epidemiological studies that diets high in fruits and vegetables might help decrease the risk of cardiovascular disease. Therefore, supplements of vitamins C and E were applied through protocols aimed to prevent diseases such as atherosclerosis, preeclampsia or hypertension, thought to be mediated by oxidative stress. Despite the biological properties of these vitamins could account for an effective protection, as shown by several clinical and experimental studies, their efficacy remains controversial in the light of some recent clinical trials and meta-analyses. However, the methodology of these studies, criteria for selection of patients, the uncertain extent of progression of the disease when initiating supplementation, the lack of mechanistic studies containing basic scientific aspects, such as the bioavailability, pharmacokinetic properties, and the nature of the antioxidant sources of vitamins, could account for the inconsistency of the various clinical trials and meta-analyses assessing the efficacy of these vitamins to prevent human diseases. This review presents a survey of the clinical use of antioxidant vitamins E and C, proposing study models based on the biological effects of these compounds likely to counteract the pathophysiological mechanisms able to explain the structural and functional organ damage.

Effect of supplementation with antioxidants upon long-term risk of hypertension in the SU.VI.MAX study: association with plasma antioxidant levels

OBJECTIVE

To assess the effects of supplementation with a combination of antioxidant vitamins and trace elements, at nutritional doses, upon the 6.5-year risk of hypertension in the SU.VI.MAX trial. To describe the association between baseline plasma antioxidant levels and the same long-term risk using observational data from the study.

SETTING

A total of 5086 adults from the SU.VI.MAX trial, a randomized primary prevention trial.

RESULTS

Compared with the placebo group, no effect of supplementation upon the 6.5-year risk of hypertension could be detected (odds ratio, 1.04 and 95% confidence interval, 0.87-1.23 in men; and odds ratio, 1.10 and 95% confidence interval, 0.95-1.29 in women). Furthermore, compared with men in the first tertile, those in the second and third tertiles of serum baseline levels of beta-carotene presented a lower risk of hypertension in both the placebo and supplementation groups. Multivariate-adjusted odds ratios (95% confidence interval) were 0.70 (0.44-1.12) and 0.53 (0.33-0.86) in the placebo group, and were 0.59 (0.37-0.94) and 0.67 (0.42-1.07) in the supplementation group. In women, a decreasing trend was observed with vitamin C levels and risk of hypertension in the intervention group. No association could be shown between vitamin E and trace element plasma levels and the risk of hypertension.

CONCLUSIONS

Despite an inverse association between baseline plasma levels of beta-carotene in men and the risk of developing hypertension, we could not demonstrate any beneficial effect of low-dose antioxidant supplementation upon the 6.5-year risk of hypertension in the randomized analysis.

Pathophysiological basis for the prophylaxis of preeclampsia through early supplementation with antioxidant vitamins

Preeclampsia (PE) is a multisystem disorder that remains a major cause of maternal and foetal morbidity and death. To date, no treatment has been found that prevents the development of the disease. Endothelial dysfunction is considered to underlie its clinical manifestations, such as maternal hypertension, proteinuria, and edema; however, the precise biochemical pathways involved remain unclear. A current hypothesis invokes the occurrence of oxidative stress as pathogenically important, as suggested by the fact that in PE, the placental and circulating levels of lipid peroxidation products (F2-isoprostanes and malondialdehyde [MDA]) are increased and endothelial cells are activated. A potential mechanism for endothelial dysfunction may occur via nuclear transcription factor kappa B (NF-kappaB) activation by oxidative stress. Alternatively, the idea that the antiangiogenic placental soluble fms-like tyrosine kinase 1 factor (sFlt1) is involved in the pathogenesis of this disease is just emerging; however, other pathophysiological events seem to precede its increased production. This review is focused on evidence providing a pathophysiological basis for the beneficial effect of early antioxidant therapy in the prevention of PE, mainly supported by the biological effects of vitamins C and E.

Prevention of fructose-induced hypertension by dietary vitamins

Essential hypertension in humans may develop through a combination of genetic and environmental factors. Diet has long been under investigation as a potential effector of blood pressure. A diet high in sucrose or fructose can give rise to hyperlipidemia, insulin resistance and hypertension. Insulin resistance, glucose intolerance and oxidative stress are common features of hypertension. If glucose metabolism through the glycolytic pathway is impaired, as in insulin resistance, there will be a build-up of glyceraldehyde, glyceraldehyde-3-phosphate and dihydroxyacetone phosphate with further metabolism to methylglyoxal, a highly reactive ketoaldehyde. Excess aldehydes can bind sulfhydryl groups of membrane proteins, altering membrane calcium channels, increasing cytosolic free calcium, peripheral vascular resistance and blood pressure. The presence of reactive aldehydes can also lead to oxidative stress. Dietary management through lower sucrose or fructose intake and increased consumption of vitamins improves glucose metabolism, lowers tissue aldehydes, increases anti-oxidant capacity and may also prevent hypertension.

Micronutrient Deficiencies as Predisposing Factors for Hypertension in Lacto-Vegetarian Indian Adults

OBJECTIVE

With the increasing knowledge about the antioxidant potential of many micronutrients such as zinc and vitamin C, their roles in oxidative stress related health disorders have been postulated. This study therefore investigated low micronutrient status as a predisposing factor for hypertension in a traditionally lacto-vegetarian population like Indians.

METHODS

Micronutrient profile was assessed in 109 hypertensives with age-gender-socio-economic status matched 115 healthy normotensives (30-58 years of age). Food intakes were estimated through a semi-quantitative food frequency questionnaire. Nutrient intakes were then evaluated by previous estimates of cooked foods from our laboratory. Systolic and diastolic blood pressure (SBP, DBP), age, weight, height, waist and hip circumference, occupation, physical activity, smoking habits were recorded. Fasting blood samples were analyzed for hemoglobin, serum level of glucose, triglycerides, total cholesterol, HDL, ceruloplasmin, plasma level of ascorbic acid, folic acid, retinol, erythrocyte glutathione reductase activity coefficient (EGRAC) and erythrocyte membrane zinc.

RESULTS

There were no significant differences between protein, fat intakes of normal and hypertensive individuals, though intakes of men were higher than those of women (p < 0.05). Intakes of omega-6 fatty acids were higher (p = 0.08) and omega-3 fatty acids were lower in hypertensive men than normotensive men (p = 0.04). Gender differences were also significant for micronutrient intakes except vitamin C and beta-carotene. Intakes of potassium, copper, folic acid and vitamin C were significantly lower in hypertensive individuals than in normotenisves. No significant association was found between occupation or activity level and hypertension (p > 0.2) in these subjects. Conditional logistic regression analysis indicated that intakes of vitamin C, folic acid and zinc were associated with 18% (OR = 1.18, 95% CI:1.08, 1.26), 51% (OR = 1.51, 95% CI 0.94, 2.1) higher odds for hypertension, and 3% lower odds for hypertension (OR = 0.97, 95% CI 0.92, 1.01), respectively. Mean plasma vitamin C and folic acid were significantly higher (p < 0.01), and serum ceruloplasmin and erythrocyte membrane zinc were marginally higher (p = 0.07) in normal than hypertensive subjects. In multivariate linear regression analyses, plasma vitamin C, serum ceruloplasmin and erythrocyte membrane zinc were negatively associated with SBP (p = 0.00001) and plasma vitamin C was negatively associated with DBP (p = 0.0001).

CONCLUSION

Low dietary intakes of vitamin C, folic acid and zinc emerged as the possible risk factors for hypertension. Further, lower levels of plasma vitamin C, erythrocyte membrane zinc and ceruloplasmin were found to be the putative intermediary biomarkers in pathogenesis of hypertension.

Antioxidant vitamins and blood pressure

Synthesis of free radicals might play a role in the cellular process of atherosclerosis. This process can be stopped by antioxidants such as beta-carotene, vitamin C, or vitamin E, which will inactivate the effects of free radicals. Although antioxidant vitamins have not been proven to prevent cardiovascular diseases through the modulation of lipid peroxidation, it has been suggested that peroxidation might be a pathway to such prevention, mediated through the effects of antioxidants on blood pressure (BP) and arterial stiffness. Several observational epidemiologic studies and some clinical trials have suggested an inverse association between dietary intake of fruits and vegetables, and BP. An inverse link between serum levels of vitamin C and BP has also been determined in observational epidemiologic settings. Some relations between other antioxidant vitamins (retinol and beta-carotene) and BP are reported; they confer the same inverse association. However, results from clinical trials testing the effect of a single, or a combination of antioxidants at high pharmacologic doses have revealed inconsistent BP findings. So far, no evidence confirms that oral antioxidant supplementation is effective in preventing or treating high BP. Additional large studies should be conducted to determine the effect on BP of antioxidant supplementation at nutritional doses.

Serum antioxidant vitamins and blood pressure in the United States population

Serum vitamin C has been inversely associated with blood pressure in several epidemiologic studies, but little is known about effect of other antioxidant vitamins. We examined the relation between serum vitamins A, C, and E, alpha-carotene, and beta-carotene levels and blood pressure among 15 317 men and women > or =20 years of age who participated in the Third National Health and Nutrition Examination Survey. Blood pressure was characterized as the average of 6 measurements obtained over 2 visits by trained observers and hypertension was defined as blood pressure > or =140/90 mm Hg and/or taking antihypertensive medications. In multivariate models, a 1 SD difference in vitamin A (16.2 microg/dL) and vitamin E (20.4 microg/dL) was associated with a 43% (OR, 1.43; 95% CI, 1.34 to 1.53) and 18% (OR, 1.18; 95% CI, 1.09 to 1.27) higher odds of hypertension, respectively. A 1 SD difference in alpha-carotene (0.47 micro g/dL) and beta-carotene (496 microg/dL) was associated with a 16% (OR, 0.84; 95% CI, 0.76 to 0.94) and 11% (OR, 0.89; 95% CI, 0.82 to 0.97) lower odds of hypertension, respectively. In addition, serum vitamins A and E were positively and significantly associated with both systolic and diastolic blood pressure, whereas alpha-carotene and beta-carotene were inversely and significantly associated with systolic and vitamin C associated with diastolic blood pressure in multivariate linear regression analyses. These findings indicate that antioxidant vitamins may be important in the underlying cause and prevention of hypertension. Further studies in this important area are warranted.

Lack of long-term effect of vitamin C supplementation on blood pressure

In a double-blinded randomized controlled trial, we investigated the long-term effect of vitamin C supplementation on blood pressure. A total of 439 Japanese subjects with atrophic gastritis initially participated in the trial using vitamin C and beta-carotene to prevent gastric cancer. Before and on early termination of beta-carotene supplementation, 134 subjects dropped out of this trial, whereas 120 and 124 subjects took the vitamin C supplement daily at either 50 mg or 500 mg, respectively, for 5 years. Before supplementation, neither systolic nor diastolic blood pressure was significantly related with the serum vitamin C concentration. This relationship was unchanged after adjustment for age, body mass index, and alcohol intake or after stratification by gender. After 5 years, systolic blood pressure significantly increased in groups, regardless of vitamin C dose, compared with baseline. Systolic blood pressure in the high-dose group (500 mg daily) increased from 125.4 to 131.7 mm Hg (5.88 mm Hg increase; 95% confidence interval [CI], 3.11 to 8.65). This value was similar with that of the low-dose group (5.73 mm Hg increase; 95% CI, 2.62 to 8.83) and of the dropout group (4.52 mm Hg increase; 95% CI, 1.26 to 7.77). There was no difference in change of diastolic blood pressure among the 3 groups. In conclusion, we observed no reduction in blood pressure with long-term moderate doses (500 mg/day) of vitamin C supplementation in a high-risk population for stomach cancer and stroke.

Dietary vitamin E and C supplementation prevents fructose induced hypertension in rats

In fructose-induced hypertension in Wistar-Kyoto (WKY) rats, excess endogenous aldehydes bind sulfhydryl groups of membrane proteins, altering membrane Ca2+ channels and increasing cytosolic free calcium and blood pressure. The thiol compound N-acetyl cysteine prevents fructose-induced hypertension by binding excess endogenous aldehydes and normalizing membrane Ca2+ channels and cytosolic free calcium. The aim of the present study was to investigate whether dietary supplementation of vitamin E and vitamin C which are known to increase tissue glutathione, a storage form of cysteine, prevents this hypertension and its associated biochemical and histopathological changes. Starting at 7 weeks of age, animals were divided into four groups of six animals each and treated as follows: control group, normal diet and normal drinking water; fructose group, normal diet and 4% fructose in drinking water; fructose + vitamin E group, diet supplemented with vitamin E (34 mg/ kg feed) and 4% fructose in drinking water; fructose + vitamin C group, diet supplemented with vitamin C (1,000 mg/kg feed) and 4% fructose in drinking water. At 14 weeks, systolic blood pressure, platelet [Ca2+]i and kidney and aortic aldehyde conjugates were significantly higher in the fructose group. These animals also displayed smooth muscle cell hyperplasia in the small arteries and arterioles of the kidneys. Dietary vitamin E and C supplementation in fructose-treated WKY rats prevented the increase in systolic blood pressure by normalizing cytosolic [Ca2+]i and kidney and aortic aldehyde conjugates and preventing adverse renal vascular changes.

A randomized, double-blind, controlled trial of vitamin C in the management of hypertension and lipids

The effect of vitamin C on blood pressure is not well established. This is a randomized, double-blind control trial. Eligible patients were followed for 8 months. Patients were randomized to 500, 1000, or 2000 mg vitamin C. During each visit, a history including medication change was obtained and standardized blood pressure measurements were performed. A 1-week dietary diary was filled out before each visit. Multiple regression analysis and subsequent multiple comparisons were used for data analysis. Fifty-four patients satisfied our criteria and agreed to participate. Thirty-one patients (mean age, 62 +/- 2 years; 52% men, 90% whites) were randomized to the three doses of vitamin C. Overall compliance was 48 +/- 2%. Both mean systolic blood pressure (SBP) and diastolic blood pressure (DBP) decreased during the vitamin C supplementation phase [mean SBP dropped by 4.5 +/- 1.8 mm Hg (P <.05) and DBP by 2.8 +/- 1.2 mm Hg (P <.05)]. There was no difference between the three vitamin C groups (P =.48). This effect was significant for only 1 month of supplementation, but the trend persisted. There was no reported intolerance to vitamin C. There was no change in lipid levels after 6 months of treatment. Vitamin C supplementation lowers blood pressure in mildly hypertensive patients. There is no additional benefit for a higher dose than 500 mg daily. The effect of vitamin C is most likely to be only short term.

Antioxidant vitamins in the prevention of cardiovascular disease: a systematic review

Do antioxidant vitamins, in regular food or as food supplements, protect against myocardial infarction and stroke? In this systematic literature review on the effects of antioxidant vitamins in the primary prevention of cardiovascular disorders, studies with ischaemic heart disease, stroke or combined cardiovascular events as end-points have been included. Studies on the effects of antioxidant vitamins on intermediary end-points (such as blood lipids and blood pressure) and as secondary prevention in patients with manifest cardiovascular disease are reviewed in a conventional manner. In observational studies (case-control or cohort design), people with high intake of antioxidant vitamins by regular diet or as food supplements generally have a lower risk of myocardial infarction and stroke than people who are low-consumers of antioxidant vitamins. The associations in observation studies have been shown for carotene, ascorbic acid as well as tocopherol. In randomized controlled trials, however, antioxidant vitamins as food supplements have no beneficial effects in the primary prevention of myocardial infarction and stroke. Serious adverse events have been reported. After an initial enthusiasm for antioxidants in the secondary prevention of cardiovascular disease, recent reports from of several large randomized trials have failed to show any beneficial effects. Thus, the apparent beneficial results of high intake of antioxidant vitamins reported in observational studies have not been confirmed in large randomized trials. The discrepancy between different types of studies is probably explained by the fact that supplement use is a component in a cluster of healthy behaviour. Antioxidant vitamins as food supplements cannot be recommended in the primary or secondary prevention against cardiovascular disease.

Relationship of serum antioxidant vitamins to serum creatinine in the US population

Several small clinical studies have reported that serum vitamin A levels were higher but serum vitamin C levels were lower among patients with end-stage renal disease. However, the relationship of antioxidant vitamins to renal function has not been studied in the general population. We examined the relationship of serum antioxidant vitamin levels to serum creatinine levels and risk for hypercreatininemia in a representative sample of 6,629 non-Hispanic whites, 4,411 non-Hispanic blacks, and 4,480 Mexican Americans aged 18 years or older who participated in the Third National Health and Nutrition Examination Survey. Serum antioxidant vitamins were measured by isocratic high-performance liquid chromatography, and serum creatinine levels, by the modified kinetic Jaffé method. Serum vitamin A level was positively and significantly associated with serum creatinine level, whereas serum vitamin C level was inversely and significantly associated with serum creatinine level. A one-SD higher level of serum vitamin A (16.9 microg/dL) was associated with a 2.53-fold (95% confidence interval, 1.96 to 3.27; P < 0.001), 2.07-fold (95% confidence interval, 1.84 to 2.33; P < 0.001), and 2.76-fold (95% confidence interval, 1.74 to 4.37; P < 0.001) greater risk for hypercreatininemia among non-Hispanic whites, non-Hispanic blacks, and Mexican Americans, respectively. A one-SD higher serum vitamin C level (0.45 mg/dL) was associated with a 22% (95% confidence interval, 0.06 to 0.35; P = 0.01) and 42% (95% confidence interval, 0.08 to 0.62; P = 0.02) lower risk for hypercreatininemia in non-Hispanic whites and Mexican Americans. Our study provides useful information to support the hypothesis that antioxidant vitamins may have an important role in the pathogenesis of chronic renal failure.

Antioxidants, vitamin C and dithiothreitol, activate membrane-bound guanylate cyclase in PC12 cells

Antioxidants and antioxidant enzymes are known to protect against cell death induced by reactive oxygen species. However, apart from directly quenching free radicals, little is known about the effect of antioxidants on hormone-activated second messenger systems. We previously found that antioxidants such as 17-beta estradiol and resveratrol activate membrane-bound guanylate cyclase GC-A, the receptor for atrial natriuretic factor (ANF), in PC12 cells. It is possible that other antioxidants may also activate membrane-bound guanylate cyclase GC-A. The aim of this study was to determine if dithiothreitol (DTT), vitamin C, and vitamin E activate membrane-bound guanylate cyclase GC-A in PC12 cells. The results showed that both DTT and vitamin C increased cGMP levels in PC12 cells, whereas vitamin E had no effect. DTT and vitamin C inhibited membrane-bound guanylate cyclase activity stimulated by ANF in PC12 cells. In contrast, DTT and vitamin C had no effect on soluble guanylate cyclase activity stimulated by substance P. Furthermore, NO synthase inhibitors L-NAME and aminoguanidine did not affect DTT- and vitamin C-stimulated guanylate cyclase activity. The results indicate that DTT and vitamin C, but not vitamin E, activate membrane-bound guanylate cyclase GC-A in PC12 cells.

Dietary vitamin C supplementation lowers blood pressure in spontaneously hypertensive rats

In spontaneously hypertensive rats (SHRs) excess endogenous aldehydes bind sulfhydryl groups of membrane proteins, altering membrane Ca2+ channels and increasing cytosolic free calcium and blood pressure. The thiol compound, N-acetyl cysteine, normalizes elevated blood pressure in SHRs by binding excess endogenous aldehydes. Vitamin C can increase tissue cysteine and glutathione levels. The aim of the present study was to investigate whether a dietary supplementation of vitamin C can lower tissue aldehydes and blood pressure and normalize associated biochemical and histopathological changes in SHRs. Starting at 12 weeks of age, animals were divided into 3 groups of 6 animals each. Animals in the WKY-control group and SHR-control group were given a normal diet and the SHR-vitamin C group a diet supplemented with vitamin C (1000 mg/kg feed) for the next 9 weeks. After nine weeks, systolic blood pressure, platelet [Ca2+]i, plasma insulin and liver, kidney and aortic aldehyde conjugates were significantly higher in SHR controls as compared to WKY controls and the SHR-vitamin C group. SHR-controls also showed smooth muscle cell hyperplasia in the small arteries and arterioles of the kidneys. Dietary vitamin C supplementation in SHRs lowered the systolic blood pressure, tissue aldehyde conjugates and attenuated adverse renal vascular changes.

Vitamin E and C in preeclampsia

Vascular endothelial damage has been implicated in the pathophysiology of preeclampsia. Lipid peroxidation may be involved in the process and essential nutrients that can scavenge free radicals, such as vitamin E and C, operate in concert. Antioxidant vitamins E and C were estimated in 30 preeclamptic and 30 normotensive pregnant women. Significantly lowered levels of vitamins E and C were observed in preeclamptic women as compared to controls (P<0.001 and P<0.05 respectively). In patients with preeclampsia antioxidant nutrients may be utilized to a greater extent to counteract free radical-mediated cell disturbances, resulting in a reduction in serum antioxidant levels.

Effect of vitamin C on ambulatory blood pressure and plasma lipids in older persons

OBJECTIVES

To determine the effect of oral vitamin C supplements on ambulatory blood pressure and plasma lipids.

DESIGN

A 6-month double-blind randomized placebo-controlled cross-over study with a 1 -week washout between cross-over periods.

METHODS

Vitamin C 500 mg daily or matching placebo was given to 40 men and women aged between 60 and 80 years for 3 months each in a cross-over fashion. Clinic and 24-h ambulatory blood pressure, plasma ascorbate and lipids were measured at baseline and at the end of each cross-over phase.

RESULTS

Clinic blood pressure did not change between placebo and vitamin C phases. Daytime ambulatory blood pressure showed a small but significant fall in systolic blood pressure (2.0 +/- 5.2 mmHg; 95% confidence interval 0-3.9 mmHg) but not in diastolic blood pressure. Regression analysis showed that with increasing baseline daytime blood pressure the fall in blood pressure with vitamin C supplementation increased. Regression analysis of the change in high-density lipoprotein (HDL) cholesterol showed a significant effect of sex on the change in HDL cholesterol. In women, but not men, HDL cholesterol increased significantly by 0.08 +/- 0.11 mmol/l, P=0.007. There was no change in low-density lipoprotein cholesterol between treatment periods.

CONCLUSION

In older adults high intakes of ascorbic acid have modest effects on lowering high systolic blood pressure, which could contribute to the reported association between higher vitamin C intake and lower risk of cardiovascular disease and stroke.

Effects of vitamin E and glutathione on glucose metabolism: role of magnesium

Vitamin E is an antioxidant that has been demonstrated to improve insulin action. Glutathione, another natural antioxidant, may also be important in blood pressure and glucose homeostasis, consistent with the involvement of free radicals in both essential hypertension and diabetes mellitus. Our group has recently suggested that the effects of reduced glutathione on glucose metabolism may be mediated, at least in part, by intracellular magnesium levels (Mg([i])). Recent evidence suggests that vitamin E enhances glutathione levels and may play a protective role in magnesium deficiency-induced cardiac lesions. To directly investigate the effects of vitamin E supplementation on insulin sensitivity in hypertension, in relation to the effects on circulating levels of reduced (GSH) and oxidized (GSSG) glutathione and on Mg([i]), we performed a 4-week, double-blind, randomized study of vitamin E administration (600 mg/d) versus placebo in 24 hypertensive patients and measured whole-body glucose disposal (WBGD) by euglycemic glucose clamp, GSH/GSSG ratios, and Mg([i]) before and after intervention. The relationships among WBGD, GSH/GSSG, and Mg([i]) in both groups were evaluated. In hypertensive subjects, vitamin E administration significantly increased WBGD (25.56+/-0.61 to 31.75+/-0.53 micromol/kg of fat-free mass per minute; P<0.01), GSH/GSSG ratio (1.10+/-0.07 to 1.65+/-0.11; P<0.01), and Mg([i]) (1.71+/-0.042 to 1.99+/-0.049 mmol/L; P<0.01). In basal conditions, WBGD was significantly related to both GSH/GSSG ratios (r=0.58, P=0.047) and Mg([i]) (r=0.78, P=0.003). These data show a clinical link between vitamin E administration, cellular magnesium, GSH/GSSG ratio, and tissue glucose metabolism. Further studies are needed to explore the cellular mechanism(s) of this association.

Toward a new recommended dietary allowance for vitamin C based on antioxidant and health effects in humans

The current recommended dietary allowance (RDA) for vitamin C for adult nonsmoking men and women is 60 mg/d, which is based on a mean requirement of 46 mg/d to prevent the deficiency disease scurvy. However, recent scientific evidence indicates that an increased intake of vitamin C is associated with a reduced risk of chronic diseases such as cancer, cardiovascular disease, and cataract, probably through antioxidant mechanisms. It is likely that the amount of vitamin C required to prevent scurvy is not sufficient to optimally protect against these diseases. Because the RDA is defined as "the average daily dietary intake level that is sufficient to meet the nutrient requirement of nearly all healthy individuals in a group," it is appropriate to reevaluate the RDA for vitamin C. Therefore, we reviewed the biochemical, clinical, and epidemiologic evidence to date for a role of vitamin C in chronic disease prevention. The totality of the reviewed data suggests that an intake of 90-100 mg vitamin C/d is required for optimum reduction of chronic disease risk in nonsmoking men and women. This amount is about twice the amount on which the current RDA for vitamin C is based, suggesting a new RDA of 120 mg vitamin C/d.