Tocopherols plasma concentration

OCAs, therefore, may lower a-tocopherol plasma concentrations in rats receiving supplements of a-tocopherol in their diet, but an effect on human a-tocopherol metabolism has not been demonstrated. 

It is well known that excessive intake of P-carotene may lead to carotenodermia (yellow skin), and it is undoubtedly the case that some carotenoid is directly lost via the skin or through photo-oxidation in the skin. As far as is known the carotenoids are not cytotoxic or genotoxic even at concentrations up to 10 times the normal plasma concentration which may cause carotenodermia. However, they are associated with amenorrhoea in girls who may be consuming bizarre diets and, in long-term supplementation studies, with an increase in lung cancer (The Alpha-tocopherol, Beta-carotene Cancer Prevention Study Group, 1994). 

Azeredo, V. B. and N. M. Trugo (2008). Retinol, carotenoids, and tocopherols in the milk of lactating adolescents and relationships with plasma concentrations. Nutrition 24(2) 133-139. 

For vitamin C, plasma concentration was always about 40 gmol/liter and not significantly different between study days. There was, however, a significant difference between day 0 and day 10, respectively, versus day 20 in the plasma concentration for ot-tocopherol. 

The contribution of lipophilic antioxidants is small. Escobar et al. (E5) found that the TAC of lipophilic antoxidants in blood plasma was 16.5 1.5 pM and corresponded almost exclusively to a-tocopherol the concentration of this compound in the blood plasma, analyzed independently, was 17.6 0.3 pM. Popov and Lewin (PI9) found TAC of lipid-soluble antioxidants in blood plasma to be 28.0 8.1 /u.M, a value comparable with the concentration of a-tocopherol (20.5 6.6 /U.M). These (and other) results confirm that a-tocopherol is the main lipid-soluble antioxidant of blood plasma (II) and indicates that the contribution of the lipid-soluble antioxidants to TAC of blood plasma is in fact negligible, taking into account that TAC of human blood plasma is of the order of 1 mM (see later). The contribution of ascorbic acid is also low. This situation may differ considerably in other biological fluids and tissue homogenates. In seminal plasma, the concentration ratio of ascorbate to urate is about 1 (G3). Ascorbate and urate contribute 29% of the fast TRAP of human seminal plasma the share of proteins and polyphenolic compounds is 57%, whereas tyrosine contributes 15% of the slow TRAP (R14) (Table 7). Ascorbate and uric acid account for about half of TAC of human tears (K3). TAC of urine is determined mainly by urate and proteins (K5). 

In case LDL oxidation is considered as an important risk factor, the dosage of vitamin E may be important to determine a clinical effect. However, with respect to inhibition of protein kinase-C and the release of proinflammatory cytokines the intracellular transfer of RRRT (natural vitamin E) by the tocopherol-associated protein may be a crucial point. Consequently, natural vitamin E is considered more effective than the synthetic one. Since the activity on LDL oxidation was pointed out as important for the prevention of cardiovascular disease, most of the long-term trials with vitamin E were conducted at dosages >200 mg/day (about 200 lU/d). In a recent meta-analysis the association of plasma levels and mortality was studied in 1168 elderly European men and women (25). No association was found between the plasma concentration and all-cause or cause-specific mortality. 

The most commonly used index of vitamin E nutritional status is the plasma concentration of a-tocopherol because it is transported in plasma lipoproteins, it is best expressed per mole of cholesterol or per milligram of total plasma lipids (Horwitt et al., 1972 Winbauer et al., 1999). The reference range is... 

Based on the plasma concentration of a-tocopherol to prevent significant hemolysis in vitro (14 to 16 /xmol per L), the U.S./Canadian estimated average requirement is 12 mg per day, giving a Recommended Dietary Amount (RDA) of 15 mg per day (Institute of Medicine, 2000) - a 50% increase on the previous RDA (National Research Council, 1989). This increase arose partly as a result of considering only the 2R isomers in dietary intake (Section 4.1). Average intakes are of the order of 8 to 12 mg of a -tocopherol equivalent per day it would be difficult meet this reference intake without significant changes in diet or use of supplements. 

Gey (1995) has shown that there is an inverse relationship between plasma a-tocopherol and risk of ischemic heart disease over a range of 2.5 to 4.0 mmol per mol of cholesterol, and has suggested an optimum or desirable plasma concentration > 4 mmol of a-tocopherol per mol of cholesterol (>3.4 /rmol... 

A concern has been raised that phytosterol doses that are effective for cholesterol reduction may impair the absorption and lower blood concentrations of fat-soluble vitamins and antioxidants. A number of studies showed that phytosterols had no effect on plasma concentrations of vitamin D, retinol, or plasma-lipid-standardized alpha-tocopherol. Moreover, the reports of the effect of phytosterols on concentrations of blood carotenoids (lutein, lycopene, and alpha-carotene) are controversial. There seems to be general agreement that phytosterol doses >1 g/d significantly decrease LDL-C standardized beta-carotene concentrations however, it remains to be determined whether a reported 15-20% reduction in beta-carotene due to phytosterol supplementation is associated with adverse health effects. Noakes et al. found that consumption of one or more carotenoid-rich vegetable or fruit servings a day was sufficient to prevent lowering of plasma carotenoid concentrations in 46 subjects with hypercholesterolemia treated with 2.3 g of either sterol or stanol esters. 

Wang Y, Ichiba M, Oishi H, lyadomi M, Shono N, Tomokuni K. Relationship between plasma concentrations of beta-carotene and alpha-tocopherol and life-style factors and levels of DNA adducts in lymphocytes. Nutr Cancer 1997 27 69-73. 

If the prevention of oxidative DNA damage plays an important role in the cancer chemopreventive effects of dietary antioxidants, then one would expect to see an inverse relationship between antioxidant intake and biomarkers of oxidative DNA damage. Lymphocyte ascorbate concentrations were inversely associated with lymphocyte 8-oxodG concentrations in 105 men and women (r=-0.28)." However, plasma concentrations of a-tocopherol and carotenoids were positively correlated with lymphocyte concentrations of 8-oxodG in a study of 52 healthy women (r=0.29 to... 

Vitamin E In man a-tocopherol is the major form of vitamin E activity found in plasma and cells with fl- and y-tocopherol being minor components all of which are bound to lipoproteins. With a plasma concentration of 5-15 mg 1 a-tocopherol has the highest plasma concentration of any of the fat soluble vitamins. For the separation of the tocopherols, reversed-phase HPLC can be used. Though the molar... 

Y Gobel, C Schaffer, B Koletzko. Simultaneous determination of low plasma concentrations of retinol and tocopherols in preterm infants hy a high-performance hquid chromatographic micromethod. J Chromatogr 688 57-62, 1997. 

In 14 healthy adult male patients, the baseline plasma concentration of a-tocopherol before receiving oral vitamin E supplements was 23 amoPL (10.1 j,g/L), corroborating the study previously discussed. After receiving 1200 lU (800 mg) of RRR -a-tocopherol for 14 days [95], an average plasma concentration was 76 xmol/L (33.5 pg/L). In another study measuring the plasma and tissue levels of a-tocopherol as a result of continuous daily oral supplementation of vitamin E, it was shown that a maximum plateau of plasma concentration was reached at 4-5 days [96]. 

---