α-Tocopherol disappearance rates from plasma depend on lipid concentrations: studies using deuterium-labeled collard greens in younger and older adults
BACKGROUND: Little is known about α-tocopherol’s bioavailability
as a constituent of food or its dependence on a subject’s age.
OBJECTIVE: To evaluate the α-tocopherol bioavailability from food,
we used collard greens grown in deuterated water (²H collard
greens) as a source of deuterium-labeled (²H) α-tocopherol consumed
by younger and older adults in a post hoc analysis of a vitamin
K study.
DESIGN: 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-α-tocopherol). Plasma unlabeled α-tocopherol
and ²H-α-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.
RESULTS: Times (12.6 ± 2.5 h) of maximum plasma ²H-α-tocopherol
concentrations (0.82% ± 0.59% total α-tocopherol), fractional disappearance
rates (0.63 ± 0.26 pools/d), half-lives (30 ± 11 h), and
the minimum estimated ²H-α-tocopherol absorbed (24% ± 16%) did
not vary between age groups or sexes (n = 41). Unlabeled α-tocopherol
concentrations were higher in older adults (26.4 ± 8.6 μmol/L) than
in younger adults (19.3 ± 4.2 μmol/L; P = 0.0019) and correlated with
serum lipids (r = 0.4938, P = 0.0012). In addition, ²H-α-tocopherol
half-lives were correlated with lipids (r = 0.4361, P = 0.0044).
CONCLUSIONS: Paradoxically, α-tocopherol remained in circulation longer
in participants with higher serum lipids, but the ²H-α-tocopherol
absorbed was not dependent on the plasma lipid status. Neither
variable was dependent on age. These data suggest that plasma
α-tocopherol concentrations are more dependent on mechanisms that
control circulating lipids rather than those related to its absorption
and initial incorporation into plasma. This trial was registered at
clinicaltrials.gov as NCT0036232.Keywords: cholesterol, pharmacokinetics, age, bioavailability, vitamin E, triacylglyceride