Molecules having vitamin E antioxidant activity include four tocopherols (α, β, δ, and γ) and four tocotrienols (α, β, δ, and γ). α-Tocopherol is the major lipid soluble antioxidant in vivo and protects against lipid peroxidation. α-CEHC is the major urinary metabolite of α-tocopherol following vitamin E supplementation. The concentration of α-CEHC in human serum is in the range of 5-10 pmol/ml but increases significantly up to 200 pmol/ml upon supplementation with RRR-α-tocopherol. About one-third of the α-CEHC circulating in the blood is present as a glucuronide conjugate. α-CEHC was only excreted when a threshold concentration of 7-9 &#181mol α-tocopherol/g total lipid in plasma was exceeded. Therefore, excretion of α-CEHC may be considered to be a marker of optimum vitamin E intake.