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Title: Alpha-tocopherol disappearance rates from plasma depend on lipid concentrations: Studies using deuterium labeled collard greens in younger and older adults

Author
item TRABER, MARET - Oregon State University
item LEONARD, SCOTT - Oregon State University
item BOBE, GERD - Oregon State University
item FU, XUEYAN - Jean Mayer Human Nutrition Research Center On Aging At Tufts University
item SALTZMAN, EDWARD - Jean Mayer Human Nutrition Research Center On Aging At Tufts University
item Grusak, Michael
item BOOTH, SARAH - Jean Mayer Human Nutrition Research Center On Aging At Tufts University

Submitted to: The American Journal of Clinical Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/23/2015
Publication Date: 4/1/2015
Citation: Traber, M.G., Leonard, S.W., Bobe, G., Fu, X., Saltzman, E., Grusak, M.A., Booth, S.L. 2015. Alpha-tocopherol disappearance rates from plasma depend on lipid concentrations: Studies using deuterium labeled collard greens in younger and older adults. American Journal of Clinical Nutrition. 101(4):752-759.

Interpretive Summary: Vitamin E, in the form of alpha-tocopherol, is an essential nutrient that is found as a constituent of certain foods. Little is known about how well it is absorbed from different foods, or whether a person's age will influence this process. To evaluate the absorption of alpha-tocopherol from food, we grew collard green plants in a special form of water that allowed us to safely tag (or mark) the alpha-tocopherol produced in the collard green leaves. Groups of younger (average age of 32 years) and older (average age of 67 years) men and women were fed a test breakfast that included the specially grown collard greens. Blood samples were collected from the subjects at various time points over the course of a few days, following the consumption of the test meal. Tagged (collard green) and untagged (derived from other food) alpha-tocopherol levels were measured in the liquid fraction of each blood sample. No differences were found between age groups or sexes for the rate of appearance or disappearance of the tagged alpha-tocopherol in blood, or for the estimated amount of tagged alpha-tocopherol that was absorbed. The results did show that alpha-tocopherol concentrations were higher in older adults than in younger adults and that these levels were correlated with the concentration of blood lipids. Interestingly, untagged alpha-tocopherol remained in circulation longer in subjects with higher blood lipid levels, but the amount of alpha-tocopherol absorbed was not dependent on these lipid levels. These data suggest that circulating levels of alpha-tocopherol are more dependent on mechanisms that control circulating lipids, rather than on mechanisms related to its absorption and initial transfer into blood. These findings have important public health consequences, because they demonstrate that one's vitamin E status cannot be assessed by only measuring blood alpha-tocopherol concentrations.

Technical Abstract: Little is known about alpha-tocopherol's bioavailability as a constituent of food or its dependence on a subject's age. To evaluate the alpha-tocopherol bioavailability from food, we used collard greens grown in deuterated water (2H collard greens) as a source of deuterium-labeled (2H) alpha-tocopherol consumed by younger and older adults in a post hoc analysis of a vitamin K study. Younger (mean +/- SD age: 32 +/- 7 y; n = 12 women and 9 men) and older (aged 67 +/- 8 y; n = 8 women and 12 men) adults consumed a test breakfast that included 120 g 2H collard greens (1.2 +/- 0.1 mg 2H-alpha-tocopherol). Plasma unlabeled alpha-tocopherol and 2H-alpha-tocopherol were measured by using liquid chromatography-mass spectrometry from fasting (>12 h) blood samples drawn before breakfast (0 h) and at 24, 48, and 72 h and from postprandial samples collected at 4, 5, 6, 7, 9, 12, and 16 h. Times (12.6 +/- 2.5 h) of maximum plasma 2H-alpha-tocopherol concentrations (0.82% +/- 0.59% total alpha-tocopherol), fractional disappearance rates (0.63 +/- 0.26 pools/d), half-lives (30 +/- 11 h), and the minimum estimated 2H-alpha-tocopherol absorbed (24% +/- 16%) did not vary between age groups or sexes (n = 41). Unlabeled alpha-tocopherol concentrations were higher in older adults (26.4 +/- 8.6 mmol/L) than in younger adults (19.3 +/- 4.2 mmol/L; P = 0.0019) and correlated with serum lipids (r = 0.4938, P = 0.0012). In addition, 2H-alpha-tocopherol half-lives were correlated with lipids (r = 0.4361, P = 0.0044). Paradoxically, alpha-tocopherol remained in circulation longer in participants with higher serum lipids, but the 2H-alpha-tocopherol absorbed was not dependent on the plasma lipid status. Neither variable was dependent on age. These data suggest that plasma alpha-tocopherol concentrations are more dependent on mechanisms that control circulating lipids rather than those related to its absorption and initial incorporation into plasma.