Vitamin E in cranes: reference ranges and nutrient interactions.

Fat soluble vitamins E and A (quantified as alpha-tocopherol and all-trans retinol, respectively) were measured in plasma samples from 274 captive cranes from four institutions and five free-ranging birds. Ages ranged from 4 mo to 80 yr, and all 15 crane species were represented. Captive cranes had a mean +/- standard error (SE) of 6.57 +/- 0.82 micrograms/ml alpha-tocopherol; migrating greater sandhill cranes (Grus canadenis tabida) had a plasma concentration of 3.71 +/- 0.22 micrograms/ml. Sex and age differences were not significant, but crane species that evolved in temperate habitats had higher circulating levels of alpha-tocopherol than tropical or subtropical species. Mean +/- SE retinol values were 0.69 +/- 0.05 micrograms/ml in captive cranes, and 0.66 +/- 0.08 micrograms/ml in free-ranging cranes; values did not differ significantly by sex, age, or species. Dietary vitamin E concentrations were significantly correlated with plasma alpha-tocopherol levels in a logarithmic relationship. Dietary selenium at 0.5 mg/kg was associated with decreased circulating alpha-tocopherol concentrations.