Vitamin E inadequacy in humans: causes and consequences

Abstract

It is estimated that >90% of Americans do not consume sufficient dietary vitamin E, as α-tocopherol, to meet estimated average requirements. What are the adverse consequences of inadequate dietary α-tocopherol intakes? This review discusses health aspects where inadequate vitamin E status is detrimental and additional vitamin E has reversed the symptoms. In general, plasma α-tocopherol concentrations <12 μmol/L are associated with increased infection, anemia, stunting of growth, and poor outcomes during pregnancy for both the infant and the mother. When low dietary amounts of α-tocopherol are consumed, tissue α-tocopherol needs exceed amounts available, leading to increased damage to target tissues. Seemingly, adequacy of human vitamin E status cannot be assessed from circulating α-tocopherol concentrations, but inadequacy can be determined from “low” values. Circulating α-tocopherol concentrations are very difficult to interpret because, as a person ages, plasma lipid concentrations also increase and these elevations in lipids increase the plasma carriers for α-tocopherol, leading to higher circulating α-tocopherol concentrations. However, abnormal lipoprotein metabolism does not necessarily increase α-tocopherol delivery to tissues. Additional biomarkers of inadequate vitamin E status are needed. Urinary excretion of the vitamin E metabolite α-carboxy-ethyl-hydroxychromanol may fulfill this biomarker role, but it has not been widely studied with regard to vitamin E status in humans or with regard to health benefits. This review evaluated the information available on the adverse consequences of inadequate α-tocopherol status and provides suggestions for avenues for research.

FIGURE 1

Plasma α-tocopherol concentrations are shown from various reports of children with potentially low vitamin E status. The bars and error bars indicate overall means ± SDs of all data points, and the individual data points represent mean or median values from specific research reports. Plasma α-tocopherol concentrations fell into 3 categories: deficient (<9 μmol/L), marginal (9–12 μmol/L), and adequate (>12 μmol/L). References for these reports are as follows: deficient (, –, –138), marginal (, –143), adequate (–, –, –146).

FIGURE 2

Hypothetical relation between dietary α-tocopherol intakes, plasma α-tocopherol concentrations, and urinary excretion of α-carboxy-ethyl-hydroxychromanol (α-CEHC). These hypothetical relations were based on data from published reports (11, 45, 61) with the assumption that as dietary α-tocopherol intakes increase, plasma α-tocopherol concentrations (solid line, left y-axis) reach a plateau. This nexus is the point at which the urinary α-CEHC excretion (dashed line, right y-axis) begins an exponential increase.