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Cardiovascular diseases (CVD) cause about 1/3 of global deaths. Therefore, new strategies for the prevention and treatment of cardiovascular events are highly sought-after. Vitamin E is known for significant antioxidative and anti-inflammatory properties, and has been studied in the prevention of CVD, supported by findings that vitamin E deficiency is associated with increased risk of cardiovascular events. However, randomized controlled trials in humans reveal conflicting and ultimately disappointing results regarding the reduction of cardiovascular events with vitamin E supplementation. As we discuss in detail, this outcome is strongly affected by study design, cohort selection, co-morbidities, genetic variations, age, and gender. For effective chronic primary and secondary prevention by vitamin E, oxidative and inflammatory status might not have been sufficiently antagonized. In contrast, acute administration of vitamin E may be more translatable into positive clinical outcomes. In patients with myocardial infarction (MI), which is associated with severe oxidative and inflammatory reactions, decreased plasma levels of vitamin E have been found. The offsetting of this acute vitamin E deficiency via short-term treatment in MI has shown promising results, and, thus, acute medication, rather than chronic supplementation, with vitamin E might revitalize vitamin E therapy and even provide positive clinical outcomes.
Cardiovascular diseases (CVD) such as atherosclerosis are a major cause of mortality and morbidity worldwide. Vitamin E is a very potent antioxidant, and shows anti-inflammatory properties . Therefore, vitamin E, particularly the α-tocopherol (α-TOH) form, has been suggested as a promising candidate in the prevention of CVD. However, enthusiastic research on vitamin E in large clinical trials has only resulted in controversial and mostly discouraging outcomes, and ultimately has not provided evidence for overall beneficial effects of vitamin E in CVD, with a few exceptions, as discussed below. The aim of the present review is to critically summarize the data available on vitamin E supplementation in CVD in general and systematically investigate potential reasons for the observed conflicting results, and we also provide a perspective on what we have learned from the past trials for future trials. We ultimately redirect the focus from chronic vitamin E supplementation to short-term vitamin E medication in acute clinical settings caused by high inflammatory and oxidative stress, such as MI.
The association between vitamin E and risk factors for cardiovascular events will be discussed in detail in the review “Cardiovascular and Metabolic Protection by Vitamin E: A Matter of Treatment Strategy?” by Melanie Ziegler, Maria Wallert, Stefan Lorkowski and Karlheinz Peter and is summarized in Table 1.
Table 1. Vitamin E and Risk Factors for Cardiovascular Events.
An early study by Gey et al. [46] found a strong inverse association between plasma vitamin E level and mortality of ischemic heart disease. Furthermore, the risk of angina pectoris was inversely associated with the plasma concentration of vitamin E in a case-controlled population study of 110 cases of angina, even after adjustment for age, smoking habit, blood pressure, lipids, and relative weight [47].
Recently, Huang et al. reported in a long-term prospective cohort study, including biochemical analysis of 29,092 participants, that higher baseline serum α-TOH was associated with lower risk of overall mortality and mortality from all major causes. This study supports the long-term health benefits of higher serum α-TOH for overall and disease-specific mortality such as CVD [48]. Several observational studies [49][50][51][52][53][54][55][56] have consistently shown that vitamin E supplementation and/or high vitamin E intake is associated with a decreased risk of CVD. To our knowledge, only one Mendelian randomization study in China showed that high vitamin E levels were associated with an increased risk of CVD [57]. Despite this study, the overall consistency in the other studies has led many to suggest that vitamin E supplements may reduce the risk of CVD and several interventional trials have begun to study the cardioprotective effect of vitamin E.
Most studies have focused on vitamin E and the risk of CVD in general, while only a few have looked at the risk of major single causes of CVD like MI. A recent study from China stated that high vitamin E levels could increase the risk of MI [57]. A prospective study by Hak et al. [58] also reported that men without a history of CVD and with higher plasma vitamin E tended to have an increased MI risk. Hense and colleagues [59] found no association between serum vitamin E concentration and MI risk in their study population; however, they suggested that this might have been due to the high average levels of vitamin E in their study population.
A high plasma level may not be associated with a lower risk of MI; nevertheless, an interesting observation is a decrease in vitamin E plasma level in MI patients [60]. Within the first 48 h after MI, the plasma level of vitamin E declines significantly by 26% [61], and remains low until the third day after the start of the catabolic response [62]. Following an infarct, Sood et al. [63] showed that reperfusion was associated with excessive oxidative stress and increased consumption of this antioxidant not only in the ischemic but also in the reperfused myocardium. Vitamin E can be suggested as a valid marker for reperfusion and supplementation of vitamin E could be a therapeutic option for antioxidative protection of the myocardium in the acute setting.
Overall, numerous observational studies have consistently reported that high vitamin E intake or supplementation is associated with a decreased risk of CVD and overall mortality. However, no interventional trials in humans has shown, so far, the benefit of a supplementation of vitamin E to prevent any cardiovascular event. In contrast, promising preclinical data [64], the decrease in vitamin E plasma level within the first 48 h after MI and the high demand for vitamin E during reperfusion justify further investigations of a short-term vitamin E supplementation in patients presenting with acute MI.