title: Plasma and dietary vitamin E in relation to insulin secretion and sensitivity.
abstract: OBJECTIVE
  In the Insulin Resistance and Atherosclerosis Study (IRAS), we have previously shown a protective effect of plasma alpha-tocopherol concentration against diabetes incidence among persons not taking vitamin E supplements. The biologic mechanism for such a protective effect could involve improvement in either insulin sensitivity (S(I)), insulin secretion or both. Thus, we examined vitamin E in relation to insulin secretion and S(I) among persons not taking vitamin E supplements.
  
  
  METHODS
  This analysis included 457 adults aged 40-69 years without a previous diabetes diagnosis or vitamin E supplement use at baseline and seen at the 5-year follow-up examination. Baseline nutrient intake was estimated from a validated 1-year food frequency questionnaire; plasma levels of alpha-tocopherol were also assessed. At follow up, a frequently sampled intravenous glucose tolerance test determined S(I), acute insulin response to glucose (AIR), and the disposition index (DI) was calculated as the sum of the log-transformed AIR and S(I) to reflect pancreatic compensation for insulin resistance.
  
  
  RESULTS
  In multivariable regression analyses, no relationship was observed for vitamin E intake and either S(I), AIR or DI. However, plasma alpha-tocopherol concentration was positively associated with log-transformed S(I) (beta= 0.27 +/- 0.09, p < 0.01) and DI (beta= 0.41 +/- 0.14, p < 0.01), but not with log-transformed AIR.
  
  
  CONCLUSIONS
  Plasma concentration of alpha-tocopherol may improve S(I) and pancreatic compensation for insulin resistance, although it does not seem to be related to acute insulin response.
authors.affiliation: Department of Epidemiology, University of Pittsburgh, Pittsburgh, PA 15213, USA. costacout@edc.pitt.edu
authors.forename: T
authors.initials: T
authors.lastname: Costacou
authors.forename: B
authors.initials: B
authors.lastname: Ma
authors.forename: I B
authors.initials: IB
authors.lastname: King
authors.forename: E J
authors.initials: EJ
authors.lastname: Mayer-Davis
mesh_terms: D000328:Adult; D000368:Aged; D001786:Blood Glucose / Q000378:metabolism*; D019587:Dietary Supplements; D005260:Female; D005951:Glucose Tolerance Test; D006801:Humans; D007328:Insulin / Q000097:blood / Q000378:metabolism*; D007333:Insulin Resistance / Q000502:physiology*; D000078790:Insulin Secretion; D008297:Male; D008875:Middle Aged; D014810:Vitamin E / Q000502:physiology; D024502:alpha-Tocopherol / Q000097:blood*
chemical_list: D001786:Blood Glucose; D007328:Insulin; D014810:Vitamin E; D024502:alpha-Tocopherol