Relationship of vitamin C status to cholesterol and blood pressure

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.

Vitamin C nutriture in newly diagnosed diabetes

This study was performed to investigate the relationship between serum L-ascorbic acid, vitamin C intake, and diabetes in a nested case-control study. A cross-sectional survey of diet and health was conducted in 2,048 adults with an age of 30 y or older in Yonchon County, Korea. An oral glucose tolerance test was administered to all participants. One hundred cases of newly diagnosed diabetes were identified. Two healthy controls for each case matched with age, gender, drinking status, and smoking status were selected among the survey participants. L-Ascorbic acid levels were analyzed in fasting serum samples and one 24-h dietary recall was performed. Dietary vitamin C intake of persons with diabetes was 50.1±47.6 mg/d and that of controls was 55.1±41.1 mg/d. People with diabetes (22.3±16.8 µmol/L) have lower serum ascorbic acid levels than their controls (26.3±17.0 µmol/L) and the difference was significant by paired t-test (p<0.01). The association between diabetes and serum ascorbic acid level was still significant in non-smokers (24.2±17.8 µmol/L for the diabetes group and 29.5±16.7 µmol/L for the control group, p<0.01) but not in smokers (19.4±15.7 µmol/L for the diabetes group and 21.2±16.0 µmol/L for the control group). Our results suggest that diabetes and smoking interactively affect serum ascorbic acid levels. Since this population had poor nutritional status of vitamin C, further investigation of association between serum ascorbic acid level and diabetes and smoking by the level of vitamin C consumption is warranted.

A randomized factorial study of the effects of long-term garlic and micronutrient supplementation and of 2-wk antibiotic treatment for Helicobacter pylori infection on serum cholesterol and lipoproteins

BACKGROUND

Little is known about the long-term effects of garlic or micronutrient supplementation on total, HDL, and LDL cholesterol in disease-free persons.

OBJECTIVE

We aimed to assess the effects of long-term supplementation with garlic and micronutrients and of short-term amoxicillin and omeprazole treatment on serum total, HDL, and LDL cholesterol in a rural Chinese population.

DESIGN

We conducted a randomized, double-blind, placebo-controlled, 2 x 2 x 2 and 2 x 2 factorial study of precancerous gastric lesions in 3411 subjects in Linqu County, Shandong Province, China. Thirty-four subjects were randomly selected from each of 12 treatment strata. Sera were analyzed at 3.3 and 7.3 y to measure effects on total, HDL, and LDL cholesterol after 2-wk twice-daily treatment with 1 g amoxicillin and 20 mg omeprazole and supplementation throughout the study with 1) 2 capsules twice daily, each containing 200 mg aged garlic extract and 1 mg steam-distilled garlic oil, or 2) twice-daily micronutrient capsules containing 250 mg vitamin C, 100 IU vitamin E, and 37.5 mg selenium.

RESULTS

Regressions adjusted for covariates indicated increases of 0.22 mmol total cholesterol/L (P = 0.01) and 0.19 mmol LDL/L (P = 0.02) after 7.3 y of micronutrient supplementation, but no effect of garlic supplementation or short-term amoxicillin and omeprazole treatment.

CONCLUSIONS

In this rural Chinese population with low meat intake and moderate cholesterol concentrations, long-term garlic supplementation had no effect on lipid profiles, whereas micronutrient supplementation was associated with small but significant increases in total and LDL-cholesterol concentrations at 7.3 y.

Alterations of the lipid profile after 7.5 years of low-dose antioxidant supplementation in the SU.VI.MAX study

Antioxidant micronutrients have been reported to be associated with an improvement in the blood profile, but the results are not consistent. The aim of the present study was to assess the effects of antioxidant supplementation on changes in the serum lipid profile of adult participants in the SU.VI.MAX study. French adults (n = 12,741: 7,713 females aged 35-60 yr, and 5,028 males aged 45-60 yr) received daily antioxidant supplementation (120 mg vitamin C, 30 mg vitamin E, 6 mg beta-carotene, 100 microg selenium, and 20 mg zinc) or a matching placebo. Median follow-up time was 7.5 yr. After 7.5 yr, no effect of supplementation on total cholesterol was observed in men or women after adjusting for baseline total cholesterol levels and lipid-lowering medications. The prevalence of hypercholesterolemia (> or =6.5 mmol/L) showed a trend toward being higher in women who received supplements compared with those who received the placebo (P= 0.06). In both sexes, the group receiving supplements exhibited higher mean serum TG concentrations than did the placebo group (P= 0.06 in men; P= 0.05 in women). The prevalence of hypertriglyceridemia (> or =2.3 mmol/L) was also significantly higher in men who received supplements (P= 0.03), but not in women. Our results suggest than long-term daily supplementation with low doses of beta-carotene, vitamins C and E, selenium, and zinc does not result in an improved lipid profile and could even adversely affect some blood lipids, possibly with a higher risk of hyperlipidemia in women.

Age-related macular degeneration and nutritional supplementation: a review of randomised controlled trials

Age-related macular degeneration (AMD) is the leading cause of severe vision loss in the developed world. The lack of effective treatment modalities, coupled with evidence supporting an oxidative pathogenesis, has increased interest in the potential preventative role of nutritional supplementation. This article reviews seven randomised controlled trials (RCTs) that have investigated the role of nutritional supplementation in AMD. Three of these trials reported a positive effect of nutritional supplementation on AMD; the Age-related eye study (AREDS), the Lutein Antioxidant Supplementation Trial (LAST), and the oral zinc trial by Newsome et al. (1988). However, the oral zinc trial by Newsome et al. (1988) was unlikely to detect any difference between treatments smaller than 72%, and the AREDS results were based on a subgroup of their study population. Lutein was considered for the AREDS formulation, but was not commercially available at that time. The findings of the LAST support a possible therapeutic role of lutein in AMD.

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.

Cardiovascular disease risk factors are lower in African-American vegans compared to lacto-ovo-vegetarians

OBJECTIVE

This study was undertaken to determine if African-American strict vegetarians (vegans) exhibit lower blood pressure (BP) and a more favorable serum lipid profile than their lacto-ovo vegetarian (LOV) counterparts, and if plasma ascorbic acid (AA) concentrations could explain any group differences in these cardiovascular disease (CVD) risk factors.

METHODS

Habitual dietary intake, anthropometric characteristics, blood pressure, and blood lipids and ascorbic acid concentrations were determined in African-American study participants (male vegans, n = 14, age = 45.6 years; male LOV, n = 49, age = 49.8; female vegans, n = 31, age = 51.1, female LOV, n = 94, age = 52.1) recruited from Seventh-Day Adventist Churches in several cities in the northeastern United States.

RESULTS

Body mass index (BMI) was significantly lower in the vegans (24.7 +/- 1.9 kg/m2) compared to LOV (26.4 +/- 0.45 kg/m2). There were no diet or gender differences in BP. Serum total cholesterol (3.75 +/- 0.12 vs. 4.51 +/- 0.10 mmol/L), LDL-cholesterol (2.06 +/- 0.13 vs. 2.65 +/- 0.09 mmol/l), and triglycerides (0.94 +/- 0.07 vs. 1.17 +/- 0.04 mmol/L) were significantly (p < 0.05) lower in vegans compared to LOV, but there were no dietary group differences in HDL-C. The ratio of total to HDL-cholesterol was significantly lower in vegans than in LOV (3.0 +/- 0.13 vs. 3.7 +/- 0.13). There were no dietary group differences in plasma AA concentrations. However, in the entire sample, plasma AA was inversely associated with BP (SBP: r = -0.46, p < 0.001, DBP: r = -0.32, p < 0.001), but unrelated to the serum lipid concentrations.

CONCLUSION

African-American vegans exhibit a more favorable serum lipid profile than lacto-ovo-vegatarians and plasma AA is inversely related to BP in African-American vegetarians but does not explain any of the differences in CVD risk factors between vegans and lacto-ovo vegetarians.

Does vitamin C reduce blood pressure? Results of a large study of people aged 65 or older

OBJECTIVE

To characterize relationships among blood pressure, pulse rate, vitamin C status and other protective and risk factors for older British people, from a national survey.

DESIGN

A cross-sectional analysis of survey data.

SETTING

A population study, representative of mainland Britain.

SUBJECTS

Among 914 people of both sexes living in the community, 373 were taking blood-pressure-lowering drugs and were therefore excluded from the analyses.

INTERVENTIONS

Completion of an interview on health, lifestyle and dietary habits, recording of a 4-day dietary record, anthropometry and taking of a blood sample to determine haematological and biochemical status.

MAIN OUTCOME MEASURES

Systolic and diastolic blood pressures, pulse rate, indices of micronutrient status including plasma ascorbate concentration, nutrient intake and haematology.

RESULTS

Plasma ascorbate concentration was inversely correlated to systolic and diastolic blood pressures and pulse rate. Other covariates of blood pressure included age, sex, domicile, plasma retinol, fibrinogen and gamma-tocopherol concentrations, erythrocyte count, prothrombin time and urine sodium: creatinine ratio. Covariates of pulse rate included sex, domicile, plasma fibrinogen and platelet count. Blood pressure was also correlated to intake of vitamin C.

CONCLUSIONS

Plasma ascorbate concentration and intake of vitamin C are covariates of blood pressure in older people living in Britain. New intervention studies are now needed, to test for possible causalities.

Vitamin C intake and cardiovascular disease risk factors in persons with non-insulin-dependent diabetes mellitus. From the Insulin Resistance Atherosclerosis Study and the San Luis Valley Diabetes Study

BACKGROUND

Persons with non-insulin-dependent diabetes mellitus (NIDDM) are at increased risk for cardiovascular disease, partly due to concomitant worsening of traditional risk factors including dyslipidemia and hypertension. Based on evidence from small, controlled clinical trials, we hypothesized that increased intake of vitamin C would be associated with improved cardiovascular disease (CVD) risk factor status among community-dwelling persons with NIDDM.

METHODS

In separate but parallel statistical analyses, hypotheses were evaluated among persons with NIDDM confirmed by WHO criteria from the Insulin Resistance Atherosclerosis Study (IRAS, n = 520) and from the San Luis Valley Diabetes Study (SLVDS, n = 422). For IRAS, diet and vitamin supplement use was assessed by food frequency interview and for SLVDS, by 24-hr dietary recall interview.

RESULTS

Mean vitamin C intake (mg/day) was 275 for IRAS and 133 for SLVDS, including supplements. In cross-sectional regression models from each data set, vitamin C intake was not associated with systolic or diastolic blood pressure nor with HDL-C, LDL-C, or triglycerides (P values > 0.10; adjusted for calories, demographic and lifestyle variables, obesity, diabetes duration, and medications). In prospective analyses including 285 SLVDS participants, baseline vitamin C intake was not related to any of these CVD risk factors measured an average of 4 years later nor to change in CVD risk factor status during the follow-up period.

CONCLUSIONS

We conclude that, across a wide range of intake, vitamin C does not appear to be associated with improved CVD risk factor status among community-dwelling persons with diabetes.

Lipid peroxidation: a review of causes, consequences, measurement and dietary influences

In this review the process of lipid peroxidation and the atherogenicity of peroxidied lipids are discussed. Recent findings with regard to the effect of selected dietary factors on susceptibility of lipids to oxidative stress and on antioxidant defences are analysed with particular reference to their potential use in the prevention and treatment of atherogenesis and, by extension, coronary heart disease. Laboratory methods of assessing antioxidant defences, lipid peroxidation and the effects of lipid peroxidation are also reviewed and discussed with particular reference to their ability to assess in vivo oxidative stress and lipid peroxidation status. A range of oxidative stress indices are presented and their limitations discussed, but the main focus is on the most commonly used laboratory test for lipid peroxidation, the thiobarbituric acid reacting substances (TBARS) test. Finally, the influence of selected dietary factors on measured peroxidation status is discussed, with particular reference to the antioxidant vitamins C (ascorbic acid) and E (alpha tocopherol) and the type of fatty acids (mono- and poly-unsaturated) in the diet.

An automated, specific, spectrophotometric method for measuring ascorbic acid in plasma (EFTSA)

OBJECTIVE

To evaluate an automated enzyme linked, ferric-tripyridyltriazine spectrophotometric assay (EFTSA) for plasma ascorbic acid.

DESIGN AND METHODS

Using aqueous ascorbic acid solutions and plasma containing native and/or added ascorbic acid, the following were assessed: reaction kinetics, dose response relationships, recovery of added ascorbic acid, specificity, precision.

RESULTS

Performing the test on a Cobas Fara centrifugal analyser, the test is linear at least to 400 micromol/L; within-run CVs at 20, 50, 140, and 300 micromol/L ascorbic acid, in both pure aqueous solutions and in plasma, were <5.5%; 99-105% of added ascorbic acid (from 30-130 micromol/L) was recovered. The reaction of ascorbic acid is virtually instantaneous; other native antioxidants do not appear to interfere, and there is no interference by dehydroascorbic acid when readings are taken within a 15-60-s reaction time window.

CONCLUSION

EFTSA appears suitable for the routine measurement of ascorbic acid in plasma.

Plasma ascorbic acid concentrations are related to cardiovascular risk factors in African-Americans

This study was undertaken to examine relationships among blood pressure, blood lipids, and plasma concentrations of ascorbic acid and malondialdehyde (MDA) equivalents (indicative of lipid peroxidation) in adult African-Americans. Subjects (n = 172, mean age = 48.0 y) were recruited from among the memberships of several Seventh-Day Adventist Churches. Plasma ascorbic acid and MDA equivalents were inversely correlated (r = -0.44, P < 0.0001). There were significant inverse correlations between plasma ascorbic acid levels and both systolic (r = -0.39, P < 0.0001) and diastolic blood pressure (r = -0.25, P < 0.03), and between plasma ascorbic acid and serum total cholesterol (r = -0.25, P < 0.03), LDL-cholesterol (LDL-C) (r = -0.33, P < 0.004), and the ratio of LDL-cholesterol to HDL-cholesterol (LDL-C/HDL-C) (r = -0.32, P < 0.004). Serum HDL-cholesterol was positively related to plasma ascorbic acid (r = 0.22, P < 0.05). The correlations for MDA equivalents and the blood pressure and blood lipid variables were of similar magnitude to those of plasma ascorbic acid, but were in the opposite direction. Multiple regression analysis revealed ascorbic acid to be a significant independent contributor to the prediction of blood pressure and LDL-C concentration. These data suggest that plasma concentrations of ascorbic acid and MDA equivalents are related to several cardiovascular risk indicators in black Americans.

The health effects of vitamin C supplementation: a review

A comprehensive review of the literature indicates that populations with long-term consumption of higher than RDA levels of vitamin C (> or = 60 mg/day) from foods and/or supplements have reduced risks of cancer at several sites, cardiovascular disease, and cataracts. The safety of higher than RDA intakes of vitamin C is confirmed in eight placebo-controlled, double-blind studies and six non-placebo clinical trials in which up to 10,000 mg of vitamin C was consumed daily for up to 3 years. There are no clinical data which suggest that vitamin C's enhancement of non-heme iron absorption in individuals with low iron status could be a critical factor in the possible increased risk of heterozygous hemochromatosis-related cardiovascular disease. In fact, the cumulative data do not confirm that iron status is related to risk of cardiovascular disease. Moreover, higher than RDA intakes of vitamin C have been associated with several indices of lowered cardiovascular disease risk including increases in HDL, and decreases in LDL oxidation, blood pressure and cardiovascular mortality.

Effect of vitamin C supplementation on lipoprotein cholesterol, apolipoprotein, and triglyceride concentrations

Plasma ascorbic acid (AA) frequently is positively correlated with high-density-lipoprotein (HDL) cholesterol and inversely related to total cholesterol concentration. To determine if vitamin C intake can alter cholesterol concentration, we examined the effect of vitamin C supplementation (1 g/d) on lipoprotein cholesterol and triglyceride levels in 138 subjects, aged 20 to 65 years, who completed an 8-month randomized, double-blinded, placebo-controlled trial. Individuals with higher levels of plasma AA (> 80 mumol/L for men and > 90 mumol/L for women), HDL cholesterol (> 1.4 mmol/L for men and > 1.7 mmol/L for women), and total cholesterol (> 6.7 mmol/L) were excluded from this trial. We observed no overall effect of supplementation on plasma concentrations of HDL, LDL, or total cholesterol, apolipoprotein (apo) B, or triglyceride. We did observe a marginally significant (P < 0.10) increase of 1.9 mumol/L (5.3 mg/dL) in apo A-I concentration with supplementation and a significant (P < 0.05) difference of 0.10 mmol/L (3.8 mg/dL) in HDL cholesterol concentration between vitamin C and placebo treatment in a nonrandomized subgroup of individuals (n = 43) and a baseline plasma AA level less than 55 mumol/L. Although the apo A-I concentration increase was only marginally significant with supplementation, change in plasma AA concentration was significantly (P < 0.05) correlated with change in apo A-I concentration in the entire sample. The overall results of this trial were negative, but our data do not allow us to rule out the possibility that vitamin C supplementation might increase HDL cholesterol or apo A-I concentrations among individuals with lower plasma AA levels.

Ascorbic acid supplementation prevents hyperlipidemia and improves myocardial performance in streptozotocin-diabetic rats

The present study investigated the effects of ascorbic acid (AA) supplementation on the cardiac performance and the plasma levels of glucose, insulin, triglycerides, cholesterol and free fatty acid in diabetic and non-diabetic rats. Diabetes was induced by intravenous injection of streptozotocin (STZ) 55 mg/kg. AA was given in drinking water in concentrations of 1 g/l or 2 g/l for 8 weeks after STZ injection. Myocardial performance was determined using the isolated perfused working heart preparations. Following AA supplementation, there were no significant changes in any of the parameters measured in non-diabetic rats; however, the occurrence of polydipsia, hyperphagia, hyperlipidemia and myocardial dysfunction in STZ-diabetic rats was significantly alleviated in a dose-dependent manner. Nevertheless, the decreased body weight gain, hypoinsulinemia and hyperglycemia in diabetic animals were not affected. The data show that AA supplementation in STZ-diabetic rats improves both hyperlipidemia and cardiac function. However, the mechanisms of these effects and the correlation between these improvements are not clear.

The role of ascorbate in antioxidant protection of biomembranes: interaction with vitamin E and coenzyme Q

One of the vital roles of ascorbic acid (vitamin C) is to act as an antioxidant to protect cellular components from free radical damage. Ascorbic acid has been shown to scavenge free radicals directly in the aqueous phases of cells and the circulatory system. Ascorbic acid has also been proven to protect membrane and other hydrophobic compartments from such damage by regenerating the antioxidant form of vitamin E. In addition, reduced coenzyme Q, also a resident of hydrophobic compartments, interacts with vitamin E to regenerate its antioxidant form. The mechanism of vitamin C antioxidant function, the myriad of pathologies resulting from its clinical deficiency, and the many health benefits it provides, are reviewed.

Vitamin C (ascorbic acid): new roles, new requirements?

There is an enormous amount of literature on vitamin C intake and health in animals, cell cultures, and humans. Beyond its function in collagen formation, ascorbic acid is known to increase absorption of inorganic iron, to have essential roles in the metabolism of folic acid and of some amino acids and hormones, and to act as an antioxidant. In recent years, research has increasingly focused on this latter function, stimulated by suggestions that "oxidative stress" may be a causal factor in the etiology of such diverse and important disorders of aging as cancer, cardiovascular disease, and cataract formation. The present evidence is strong enough to have convinced nutritionists that daily vitamin C intake should be many times higher than the amount needed to protect against scurvy, and this is reflected in the present Recommended Dietary Allowances. Suggestions that the recommended levels should be higher still are largely based on extrapolations from results of animal and tissue culture studies. How much ascorbic acid is necessary to achieve in humans the effects seen in animal studies is not clear. In general, the limited human studies have not been persuasive. The data are incomplete, and many of the studies have serious flaws. There are no toxicity studies of the type done for new compounds being considered for approval as therapy for major disease conditions. Intervention studies will be difficult, but are essential, and methods for tissue saturation measurement must be defined before new recommendations for the public are designed.