Plasma and dietary vitamin E in relation to insulin secretion and sensitivity.
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.
Costacou
T
T
Department of Epidemiology, University of Pittsburgh, Pittsburgh, PA 15213, USA. costacout@edc.pitt.edu
Ma
B
B
King
I B
IB
Mayer-Davis
E J
EJ
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*
D001786:Blood Glucose; D007328:Insulin; D014810:Vitamin E; D024502:alpha-Tocopherol