American Journal of Clinical Nutrition Dietary supplements

Effects of vitamins C and E and {beta}-carotene on the risk of type 2 diabetes in women at high risk of cardiovascular disease: a randomized controlled trial [Dietary supplements]

Song, Y., Cook, N. R, Albert, C. M, Van Denburgh, M., Manson, J. E — Mon, 20 Jul 2009 10:02:05 PDT

Background: Vitamin C, vitamin E, and β-carotene are major antioxidants and as such may protect against the development of type 2 diabetes via reduction of oxidative stress.

Objective: The purpose of this study was to investigate the long-term effects of supplementation with vitamin C, vitamin E, and β-carotene for primary prevention of type 2 diabetes.

Design: In the Women's Antioxidant Cardiovascular Study, a randomized trial that occurred between 1995 and 2005, 8171 female health professionals aged ≥40 y with either a history of cardiovascular disease (CVD) or ≥3 CVD risk factors were randomly assigned to receive vitamin C (ascorbic acid, 500 mg every day), vitamin E (RRR--tocopherol acetate, 600 IU every other day), β-carotene (50 mg every other day), or their respective placebos.

Results: During a median follow-up of 9.2 y, a total of 895 incident cases occurred among 6574 women who were free of diabetes at baseline. There was a trend toward a modest reduction in diabetes risk in women assigned to receive vitamin C compared with those assigned to receive placebo [relative risk (RR): 0.89; 95% CI: 0.78, 1.02; P = 0.09], whereas a trend for a slight elevation in diabetes risk was observed for vitamin E treatment (RR: 1.13; 95% CI: 0.99, 1.29; P = 0.07). However, neither of these effects reached statistical significance. No significant effect was observed for β-carotene treatment (RR: 0.97; 95% CI: 0.85, 1.11; P = 0.68).

Conclusion: Our randomized trial data showed no significant overall effects of vitamin C, vitamin E, and β-carotene on risk of developing type 2 diabetes in women at high risk of CVD. This trial was registered at clinicaltrials.gov as NCT00000541.

Dietary supplementation with n-3 polyunsaturated fatty acids in early childhood: effects on blood pressure and arterial structure and function at age 8 y [Dietary supplements]

Mon, 20 Jul 2009 10:02:05 PDT

Background: n–3 Fatty acid supplementation in adults results in cardiovascular benefits. However, the cardiovascular effects of n–3 supplementation in early childhood are unknown.

Objective: The objective was to evaluate blood pressure (BP) and arterial structure and function in 8-y-old children who had participated in a randomized controlled trial of dietary n–3 and n–6 modification over the first 5 y of life.

Design: The children (n = 616; 49% girls) were randomly assigned antenatally to active (n = 312; increase in n–3 intake and decrease in n–6 intake) or control (n = 304) diet interventions implemented from the time of weaning or introduction of solids until 5 y of age. At age 8.0 ± 0.1 y, BP, carotid intima-media thickness, carotid artery distensibility, augmentation index, and brachial pulse wave velocity were measured in 405 of these children. Venous blood was collected for measurement of plasma fatty acids, lipoproteins, high-sensitivity C-reactive protein, and asymmetric dimethylarginine. Plasma fatty acid concentrations were also assessed during the intervention.

Results: Plasma concentrations of n–3 fatty acids were higher and of n–6 were lower in the active than in the control diet group at 18 mo and 3 and 5 y (P < 0.0001). Concentrations of n–3 and n–6 fatty acids were similar at 8 y. At 8 y of age, no significant differences were found in BP, carotid intima-media thickness, carotid artery distensibility, augmentation index, asymmetric dimethylarginine, high-sensitivity C-reactive protein, or lipoproteins between diet groups.

Conclusion: A dietary supplement intervention to increase n–3 and decrease n–6 intakes from infancy until 5 y does not result in significant improvements in arterial structure and function at age 8 y. This trial was registered at the Australian Clinical Trials Registry as ACTRN012605000042640.

Poor vitamin C status is associated with increased carotid intima-media thickness, decreased microvascular function, and delayed myocardial repolarization in young patients with type 1 diabetes [Dietary supplements]

Odermarsky, M., Lykkesfeldt, J., Liuba, P. — Mon, 20 Jul 2009 10:02:05 PDT

Background: Vascular endothelial dysfunction, accelerated thickening of arterial intima, and changes in ventricular repolarization contribute to increased cardiovascular morbidity in type 1 diabetes (T1D). Although vitamin C has important antioxidant functions and increased oxidative stress is a central mechanism of cardiovascular dysfunction in T1D, the relation between vitamin C and the cardiovascular system in young diabetic patients has not been investigated.

Objective: In a cohort of young patients with T1D, we investigated the relation of plasma concentrations of vitamin C with indexes of vascular function and structure and duration of the QT interval corrected for heart rate (QT_c).

Design: Carotid artery intima-media thickness, cutaneous microvascular function, and duration of the QT_c interval were measured in 59 patients (mean age: 17 y; range: 10–22 y) with T1D (diabetes duration: 3–20 y). Plasma vitamin C was analyzed by HPLC with coulometric detection.

Results: Carotid artery intima-media thickness and duration of the QT_c interval were higher in patients in the lowest tertile of vitamin C than in those in the highest tertile (P < 0.05 for both). The cutaneous microvascular response to acetylcholine was lower (P = 0.003) in the lowest tertile group than in the highest tertile group, but the response to sodium nitroprusside was not significantly different between these 2 groups. All differences remained significant after adjustment for age, sex, diabetes duration, body mass index, and glycated hemoglobin.

Conclusions: In this relatively small-scale cross-sectional study of young patients with T1D, lower plasma concentrations of vitamin C seem to be associated with adverse changes in the microcirculation, peripheral arteries, and ventricular repolarization. Large-scale prospective studies are needed to confirm these results and to clarify the underlying mechanisms.