The response of gamma vitamin E to varying dosages of alpha vitamin E plus vitamin C

Abstract

Vitamin E has been studied extensively in the prevention of atherosclerosis. Cross-sectional population studies as well as randomized controlled intervention trials have demonstrated conflicting results. A recent meta-analysis of these trials has emphasized the ineffectiveness of vitamin E in atherosclerosis prevention, with a possibility of harm at higher dosages. However, vitamin E has several isomers, with the alpha form being available via dietary supplements and the gamma form being available via dietary foodstuffs. The gamma form of vitamin E demonstrates several superior properties (such as trapping reactive nitrogen species and detoxifying nitrogen dioxide) compared with alpha vitamin E. All clinical trials have used the alpha isomer, with little concern that this isomer of vitamin E may actually suppress the gamma isomer of vitamin E. We undertook a dose-response study in volunteers with type 2 diabetes mellitus to include all the dosages of alpha vitamin E that have been used in cardiovascular prevention trials to determine the effect of alpha vitamin E on gamma vitamin E. We also assessed the effect of alpha vitamin E on several traditional markers of atherosclerotic risk. We added vitamin C to the vitamin E because several clinical trials included this vitamin to enhance the antioxidant effects of alpha vitamin E. Volunteers received, in randomized order for a 2-week period, one of the following vitamin dosage arms: (1) no vitamins, (2) low-dose supplemental vitamins E plus C, (3) medium-dose supplemental vitamins E plus C, and (4) high-dose supplemental vitamins E plus C. Blood levels of both alpha and gamma vitamin E were measured as well as surrogate markers of oxidative stress, hypercoagulation, and inflammation during a high-fat atherogenic meal (to increase the ambient oxidative stress level during the study). The results demonstrate that alpha vitamin E levels increased in proportion to the dose administered. However, at every dose of alpha vitamin E, gamma vitamin E concentration was significantly suppressed. No beneficial changes in surrogate markers of atherosclerosis were observed, consistent with the negative results of prospective clinical trials using alpha vitamin E. Our results suggest that all prospective cardiovascular clinical trials that used vitamin E supplementation actually suppressed the beneficial antioxidant gamma isomer of vitamin E. No beneficial effects on several potential cardiovascular risk factors were observed, even when the vitamin E was supplemented with vitamin C. If a standardized preparation of gamma vitamin E (without the alpha isomer) becomes available, the effects of gamma vitamin E on atherosclerotic risk will warrant additional studies.

Trial registration: ClinicalTrials.gov NCT00362518.

Figure 1. Vitamin Levels

Lipid standardized plasma alpha vitamin E (A) and gamma vitamin E (B) excursions during the no vitamin arm (black square), low dose vitamin arm (black circle), medium dose vitamin arm (open triangle), and high dose vitamin arm (open diamond). All x-axis values (including the −0.25 hr value) were obtained following breakfast and should be interpreted as relative to the lunch meal. The range for the standard error of the mean (SEM) for lipid standardized alpha vitamin E at all data points was: no vitamin arm= 2.7–3.3, low dose vitamin arm= 3.8–4.6, medium dose vitamin arm= 6.0–7.3, and high dose vitamin arm= 5.7–7.2. The range for the SEM for lipid standardized gamma vitamin E at all data points was: no vitamin arm= 0.9–1.1, low dose vitamin arm= 0.2–0.5, medium dose vitamin arm= 0.2–0.3, and high dose vitamin arm= 0.2–0.3. At all doses of vitamin E supplementation, gamma vitamin E was significantly suppressed by alpha vitamin E, p<0.01.

Figure 2. Cardiovascular Risk and Oxidative Stress Markers

Plasma oxidized LDL (A), erythrocyte glutathione peroxidase activity (B), and plasma MDA (C) excursions during the no vitamin arm (black square), low dose vitamin arm (black circle), medium dose vitamin arm (open triangle), and high dose vitamin arm (open diamond). The range for the standard error of the mean (SEM) for oxidized LDL at all data points was: no vitamin arm = 4.3–5.4, low dose vitamin arm = 4.1–5.1, medium dose vitamin arm = 4.5–5.9, and high dose vitamin arm = 3.2–3.6. The range for the SEM for erythrocyte glutathione peroxidase activity at all data points was: no vitamin arm = 10.4–12.6, low dose vitamin arm = 8.5–12.3, medium dose vitamin arm = 10.0–12.1, and high dose vitamin arm = 9.3–12.9. The range for the SEM for plasma MDA at all data points was: no vitamin arm = 0.026–0.112, low dose vitamin arm = 0.037–0.331, medium dose vitamin arm = 0.040–0.098, and high dose vitamin arm = 0.032–0.166. For each of the markers of oxidative stress, no significant difference was observed between the different dosages of vitamin E supplementation, p>0.05.

Figure 3. Inflammation Markers

Plasma hsCRP (A), adiponectin (B), and hsIL-6 (C) excursions during the no vitamin arm (black square), low dose vitamin arm (black circle), medium dose vitamin arm (open triangle), and high dose vitamin arm (open diamond). The range for the standard error of the mean (SEM) for hsCRP at all data points was: no vitamin arm = 0.13–0.14, low dose vitamin arm = 0.11–0.13, medium dose vitamin arm = 0.10–0.11, and high dose vitamin arm = 0.14–0.17. The range for the SEM for adiponectin at all data points was: no vitamin arm = 1.4–1.5, low dose vitamin arm= 1.4–1.7, medium dose vitamin arm= 1.4–1.6, and high dose vitamin arm= 1.6–1.8. The range for the SEM for hsIL-6 at all data points was: no vitamin arm = 0.4–0.8, low dose vitamin arm = 0.3–0.4, medium dose vitamin arm = 0.2–0.6, and high dose vitamin arm = 0.2–0.5. For each of the markers of inflammation, no significant difference was observed between the different dosages of vitamin E supplementation, p>0.05.

Figure 4. Hypercoagulation Markers

Plasma PAI-1 (A) and fibrinogen (B) excursions during the no vitamin arm (black square), low dose vitamin arm (black circle), medium dose vitamin arm (open triangle), and high dose vitamin arm (open diamond). The range for the standard error of the mean (SEM) for PAI-1 at all data points was: no vitamin arm = 2.2–5.3, low dose vitamin arm = 2.1–4.9, medium dose vitamin arm = 2.7–5.7, and high dose vitamin arm = 2.7–4.3. The range for the SEM for fibrinogen at all data points was: no vitamin arm= 19–24, low dose vitamin arm= 12–19, medium dose vitamin arm = 13–19, and high dose vitamin arm = 18–24. For each of the markers of hypercoagulation, no significant difference was observed between the different dosages of vitamin E supplementation, p>0.05.

Figure 5. Metabolic Markers

Plasma glucose (A), insulin (B), C-peptide (C), and NEFA (D) excursions during the no vitamin arm (black square), low dose vitamin arm (black circle), medium dose vitamin arm (open triangle), and high dose vitamin arm (open diamond). The range for the standard error of the mean (SEM) for glucose at all data points was: no vitamin arm = 4–17, low dose vitamin arm = 5–21, medium dose vitamin arm = 5–21, and high dose vitamin arm = 5–17. The range for the SEM for insulin at all data points was: no vitamin arm = 8–26, low dose vitamin arm = 7–40, medium dose vitamin arm = 6–43, and high dose vitamin arm = 5–40. The range for the SEM for C-peptide at all data points was: no vitamin arm= 0.5–1.1, low dose vitamin arm= 0.5–1.2, medium dose vitamin arm= 0.6–1.1, and high dose vitamin arm= 0.5–1.0. The range for the SEM for NEFA at all data points was: no vitamin arm= 0.02–0.07, low dose vitamin arm = 0.02–0.07, medium dose vitamin arm = 0.03–0.05, and high dose vitamin arm = 0.04–0.06. Although there was no significant difference between the different dosages of vitamin E supplementation and the metabolic markers (p>0.05), the metabolic effects of the high fat are evident.