Plasma and Dietary Vitamin E in Relation to Incidence of Type 2 Diabetes

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Abstract
OBJECTIVE—To evaluate the association of vitamin E with incidence of type 2 diabetes and to do so separately among individuals who did and those who did not report regular use of vitamin supplementation. RESEARCH DESIGN AND METHODS—The Insulin Resistance Atherosclerosis Study (IRAS) included 895 nondiabetic adults at baseline (including 303 with impaired glucose tolerance [IGT]), 148 of whom developed type 2 diabetes according to World Health Organization (WHO) criteria during the 5-year follow-up. At baseline, dietary vitamin E was estimated by a validated food frequency interview, usual supplement use was confirmed by supplement label, and plasma α-tocopherol was measured. Analyses were conducted separately for individuals who did (n = 318) and did not (n = 577) use vitamin E supplements. RESULTS—Among supplement nonusers, reported mean intake of vitamin E (mg α-tocopherol equivalents [α-TE]) did not differ between those who remained nondiabetic (n = 490) and those who developed diabetes (n = 87) (10.5 ± 5.5 vs. 9.5 ± 4.8 [means ± SD], respectively, NS). After adjustment for demographic variables, obesity, physical activity, and other nutrients, the association remained nonsignificant (odds ratio [OR] 0.80, 95% CI 0.13–5.06) for the highest level of intake (≥20 mg α-TE) compared with the lowest level (1–4 α-TE). However, results for plasma concentration of α-tocopherol showed a significant protective effect both before and after adjustment for potential confounders (adjusted OR 0.12, 95% CI 0.02–0.68, for the highest quintile vs. the lowest quintile; overall test for trend, P < 0.01). Among individuals who reported habitual use of vitamin E supplements (at least once per month in the year before baseline; 259 remained nondiabetic and 59 developed diabetes), no protective effect was observed for either reported intake of vitamin E or plasma concentration of α-tocopherol CONCLUSIONS—A protective effect of vitamin E may exist within the range of intake available from food. This effect may go undetected within studies of high-dose supplement use, which appears to hold no additional protective benefit.