Plasma ascorbate and vitamin E levels in Hong Kong Chinese

Plasma Vitamin E and the Risk of First Stroke in Hypertensive Patients: A Nested Case-Control Study

Background: The association between plasma vitamin E levels and first stroke risk in men and women remains unclear. Objective: We aimed to examine the prospective association between plasma vitamin E and first stroke, and evaluate the effect modifiers for the association, among hypertensive patients. Design: The study sample was drawn from the China Stroke Primary Prevention Trial (CSPPT), which randomized a total of 20,702 hypertensive patients to a double-blind, daily treatment with either 10 mg enalapril and 0.8 mg folic acid or 10 mg enalapril alone. This nested case-control study, including 618 first stroke cases and 618 controls matched for age, sex, treatment group, and study site, was conducted after the completion of the CSPPT. Results: The median follow-up duration was 4.5 years. Among men, a significantly higher risk of first stroke (adjusted OR, 1.67; 95%CI: 1.01, 2.77) was found for those with plasma vitamin E ≥7.1 μg/mL (≥quartile 1) compared with those with plasma vitamin E < 7.1 μg/mL. Subgroup analyses further showed that the association between vitamin E (≥7.1 vs. <7.1 μg/mL) and first stroke in men was significantly stronger in non-drinkers (adjusted OR, 2.64; 95%CI: 1.41, 4.96), compared to current drinkers (adjusted OR, 0.84; 95% CI: 0.43, 1.66, P-interaction = 0.008). However, there was no significant association between plasma vitamin E and first stroke in women (P-interaction between sex and plasma vitamin E = 0.048). Conclusions: Among Chinese hypertensive patients, there was a statistically significant positive association between baseline plasma vitamin E and the risk of first stroke in men, but not in women. Clinical Trial Registration: https://clinicaltrials.gov/ct2/show/NCT00794885, Identifier: NCT00794885.

Dietary Intake of Anti-Oxidant Vitamins A, C, and E Is Inversely Associated with Adverse Cardiovascular Outcomes in Chinese-A 22-Years Population-Based Prospective Study

Background: Conflicting and population-dependent findings have been reported from epidemiological studies on the associations of dietary intake of anti-oxidant vitamins with cardiovascular events. We investigated the prospective relationship between dietary intake of anti-oxidant vitamins and incident adverse cardiovascular outcomes amongst Hong Kong Chinese. Methods: In this prospective population-based study, baseline dietary intake of anti-oxidant vitamins (A, C, and E) were assessed using a food frequency questionnaire in 875 Chinese participants from the Hong Kong Cardiovascular Risk Factor Prevalence Study (CRISPS) in 1995–1996. The adjusted hazard ratio (HR) of incident adverse cardiovascular outcomes, defined as the first recorded diagnosis of cardiovascular deaths, non-fatal myocardial infarction or non-fatal stroke, and coronary or other arterial revascularizations, was calculated per unit intake of each vitamin using multivariable Cox regression. Results: Over a median follow-up of 22 years, 85 participants (9.7%) developed adverse cardiovascular outcomes. Dietary intakes of vitamin A, C, and E were independently and inversely associated with incident adverse cardiovascular outcomes (HR 0.68, 95%CI 0.53–0.88, p = 0.003 for vitamin A; HR 0.66, 95%CI 0.52–0.85, p = 0.001 for vitamin C; and HR 0.57, 95%CI 0.38–0.86, p = 0.017 for vitamin E) after adjustments for conventional cardiovascular risk factors at baseline. Conclusions: Dietary intakes of anti-oxidant vitamins A, C, and E reduced the risk of adverse cardiovascular outcomes in Hong Kong Chinese.

Association between vitamin C deficiency and dialysis modalities

AIM

  We designed a cross-sectional study to investigate plasma vitamin C level in patients who underwent maintenance haemodialysis (MHD) and continuous ambulatory peritoneal dialysis (CAPD) to explore whether there is a difference in vitamin C deficiency between MHD patients and CAPD patients.

METHODS

  This investigation included 382 dialysis patients without vitamin C supplement before the study. Demographic characteristics, laboratory tests, ascorbic acid and total plasma vitamin C level were measured. A linear regression model was built to explore the association between vitamin C deficiency and dialysis modalities after adjusting for age, dialysis vintage, gender, Charlson index, modality of dialysis and hsCRP.

RESULTS

  The range of plasma vitamin C level was from 0.48 µg/mL to 31.16 µg/mL. 35.9% (n = 137) patients had severe vitamin C deficiency (<2 µg/mL). Plasma vitamin C level was inversely associated with age and dialysis vintage. After age and dialysis vintage were adjusted, vitamin C deficiency was associated with MHD. R square for model fitting was relatively low, which implied that there were other vitamin C influencing factors not included in the model.

CONCLUSIONS

  Vitamin C deficiency is common in dialysis patients, especially in patients treated with MHD.

Serum vitamin C and the prevalence of vitamin C deficiency in the United States: 2003-2004 National Health and Nutrition Examination Survey (NHANES)

BACKGROUND

Vitamin C (ascorbic acid) may be the most important water-soluble antioxidant in human plasma. In the third National Health and Nutrition Examination Survey (NHANES III, 1988-1994), approximately 13% of the US population was vitamin C deficient (serum concentrations <11.4 micromol/L).

OBJECTIVE

The aim was to determine the most current distribution of serum vitamin C concentrations in the United States and the prevalence of deficiency in selected subgroups.

DESIGN

Serum concentrations of total vitamin C were measured in 7277 noninstitutionalized civilians aged > or =6 y during the cross-sectional, nationally representative NHANES 2003-2004. The prevalence of deficiency was compared with results from NHANES III.

RESULTS

The overall age-adjusted mean from the square-root transformed (SM) concentration was 51.4 micromol/L (95% CI: 48.4, 54.6). The highest concentrations were found in children and older persons. Within each race-ethnic group, women had higher concentrations than did men (P < 0.05). Mean concentrations of adult smokers were one-third lower than those of nonsmokers (SM: 35.2 compared with 50.7 micromol/L and 38.6 compared with 58.0 micromol/L in men and women, respectively). The overall prevalence (+/-SE) of age-adjusted vitamin C deficiency was 7.1 +/- 0.9%. Mean vitamin C concentrations increased (P < 0.05) and the prevalence of vitamin C deficiency decreased (P < 0.01) with increasing socioeconomic status. Recent vitamin C supplement use or adequate dietary intake decreased the risk of vitamin C deficiency (P < 0.05).

CONCLUSIONS

In NHANES 2003-2004, vitamin C status improved, and the prevalence of vitamin C deficiency was significantly lower than that during NHANES III, but smokers and low-income persons were among those at increased risk of deficiency.

A study of the effect of oral glucose loading on plasma oxidant:antioxidant balance in normal subjects

BACKGROUND

Antioxidant defence has been reported to decrease, and oxidative stress to increase, after oral glucose loading in both normal and diabetic subjects. If confirmed in normal subjects, glucose-induced antioxidant depletion has important implications for health in relation to the modern, sugar-rich diet.

AIM OF THE STUDY

To investigate changes in plasma biomarkers of oxidant:antioxidant balance in non-diabetic subjects following oral glucose loading. Baseline inter-relationships between biomarkers of glycaemic control, oxidant:antioxidant balance and inflammation were also explored.

METHODS

A single-blinded, placebo-controlled, crossover intervention trial involving 10 healthy, consenting subjects. Venous blood was collected after ingestion of 75 g glucose in 300 mL water, or of water alone. Blood was collected at 0 time (fasting) and 30, 60, 90, 120 min post-ingestion. Within 2 weeks the procedure was repeated with volunteers crossed-over onto the other treatment. Plasma total antioxidant capacity (as the FRAP value), ascorbic acid, alpha-tocopherol, uric acid, malondialdehyde (MDA), allantoin and high sensitivity C-reactive protein (hsCRP), glucose and insulin, were measured in all samples. Paired results post-glucose and post-water at each time interval were compared using the Wilcoxon matched-pairs signed-ranks test.

RESULTS

Normal glucose tolerance was observed in all subjects, although, as expected, plasma glucose and insulin increased significantly (p < 0.05, n = 10) after glucose loading. Post-glucose responses in plasma FRAP and the individual antioxidants tested were not significantly different to the responses seen post-water, although both FRAP and alpha-tocopherol decreased slightly. Neither were post-glucose changes in plasma MDA and allantoin, putative biomarkers of oxidative stress, significantly different to those after intake of water alone. Plasma FRAP and alpha-tocopherol also decreased slightly, but not significantly, after intake of water. A significant direct correlation (r = 0.867, p < 0.001, n = 10) was found between fasting allantoin and (log transformed) hsCRP concentrations.

CONCLUSIONS

These new data from a controlled intervention trial indicate that acute, transient increases in plasma glucose following oral intake of a large glucose load do not, as previously reported, cause a significant decrease in plasma antioxidants or increase oxidative stress in non-diabetic subjects. This is reassuring given the large quantities of sugar ingested by children and adolescents. However, a small decrease in plasma antioxidant capacity was seen after ingestion of water and of glucose, and it is possible that intake of glucose without concomitant intake of antioxidants in susceptible individuals may cause oxidative stress. Further work is needed in relation to diabetic subjects and a possible glucose threshold for this. The finding of a direct relationship between allantoin, a biomarker of oxidative stress, and hsCRP, a marker of inflammation and CHD predictor, in healthy subjects is interesting and indicates a link between sub-clinical inflammation and oxidative stress.

Vitamin E supplementation improves cell-mediated immunity and oxidative stress of Asian men and women

Vitamin E is an efficient antioxidant and a modulator of the immune system. Although racial differences in both baseline vitamin E level and immunologic subsets are known, no reliable data exist for the Asian population. Furthermore, the extent of the effect of alpha-tocopherol in protecting lymphocyte cells against oxidative stress and its association with cell-mediated immunity have not been elucidated. This study was undertaken to investigate the immunologic and antioxidant effects of vitamin E in healthy ethnic Chinese men and women. Volunteers < 35 y old (n = 26) were supplemented with 233 mg/d dl-alpha-tocopherol for 28 d. The in vitro proliferative response to phytohemagglutinin (PHA) or lipopolysaccharide (LPS) of T-lymphocytes was determined in the study group before and after vitamin E supplementation. Cell-mediated immunity subsets and hydrogen peroxide production in T-lymphocytes were investigated by flow cytometry. The oxidant-antioxidant balance in plasma and urine was studied by spectrophotometric and gas chromatography-mass selective detection methods. The antioxidant properties of vitamin E were established (P: < 0.01) by the elevation of plasma vitamin E, together with depression in both plasma malondialdehyde and urinary DNA adduct 8-hydroxy-2'-deoxyguanosine after supplementation. Our data suggest a specific requirement for vitamin E in total-T and T-helper cell proliferation. We present the first evidence of the beneficial effects of supplemental vitamin E in healthy Chinese individuals on cell-mediated immunity and oxidative stress.

Vitamin C: prospective functional markers for defining optimal nutritional status

Most species of plants and animals synthesize ascorbic acid, but human subjects cannot, making vitamin C an essential component of our diet. Relationships between vitamin C intake and status, and between status and health are not yet clear. There is evidence, however, that higher intake of vitamin C is associated with lower risk of disease, supporting the concept that optimal intake is needed for optimal vitamin C status, and that both factors are required for optimal health. Vitamin C has low toxicity in healthy subjects, but a clear definition of optimal status and the dietary intake required to meet and maintain this status is needed before a change in the current recommended intake can be considered. Available evidence suggests that intake of 200 mg vitamin C/d saturates tissues and maintains fasting plasma levels above the proposed threshold (50 mumol/l) for minimum risk of CHD. However, the issue of whether or not these levels produce 'optimal vitamin C status' awaits the clear and accepted definition of the term. This definition in turn awaits the development of reliable functional markers capable of assessing the effects of varying levels of vitamin C nutriture. In the present paper the relationship between intake and body stores of vitamin C and the role of vitamin C in human health are reviewed briefly. The requirements of a reliable functional marker of human vitamin C status are defined, three classes of functional markers (molecular, biochemical and physiological) are described, and possible candidate markers are examined.