Plasma and Dietary Vitamin E in Relation to Incidence of Type 2 Diabetes The Insulin Resistance and Atherosclerosis Study (IRAS) ELIZABETH J. MAYER-DAVIS, PHD 1 TINA COSTACOU, PHD 1 IRENA KING, PHD 2 DANIEL J. ZACCARO, MS 3 RONNY A. BELL, PHD 3 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 Organi- zation (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 -tocopherol was measured. Analyses were conducted separately for individ- uals who did (n = 318) and did not (n = 577) use vitamin E supplements. RESULTS — Among supplement nonusers, reported mean intake of vitamin E (mg -toco- pherol equivalents [-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], respec- tively, 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 -TE) compared with the lowest level (1– 4 -TE). However, results for plasma concentration of -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 ob- served for either reported intake of vitamin E or plasma concentration of -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. Diabetes Care 25:2172–2177, 2002 I n 2000, the prevalence of diagnosed diabetes in the U.S. was estimated at 7.3% (1), an alarming 49% increase from 1990 (2). The economic cost result- ing from the numerous and severe com- plications of diabetes, which in 1997 was estimated at $98 billion (3), as well as the social burden associated with diabetes, have motivated the pursuit of prevention methods. Approaches for primary pre- vention of type 2 diabetes through life- style modifications that include weight management, diet, and physical activity have recently been reviewed (4). The potential for antioxidant nutri- ents, particularly vitamin E, to prevent chronic diseases, including diabetes (5), remains uncertain. Results from a 4-year cohort study showed a 22% increment in diabetes risk per 1-mol/l decrement in plasma -tocopherol levels (P = 0.0004) (6). Of interest, the vast majority of par- ticipants (932 subjects, 98.7%) did not use supplements of vitamin E. A similar study produced quantitatively similar re- sults; however, statistical significance was not achieved (7). It has been suggested that vitamin E improves insulin sensi- tivity, although studies generally have focused on the potential effect of supple- mental vitamin E on insulin sensitivity and results have been equivocal (8 –11). Therefore, we undertook this study to ex- aminethepotentialeffectofplasma -toco- pherol concentration and intake of vitamin E from foods and supplements on the development of type 2 diabetes in a large cohort of men and women who were observed in a 5-year prospective study. To clarify the range of exposure within which a beneficial effect of vitamin E may exist, we examined the data separately be- tween individuals who did and those who did not report regular use of vitamin sup- plementation. RESEARCH DESIGN AND METHODS Study design The design and methods of the Insulin Resistance and Atherosclerosis Study (IRAS) have been previously described in detail (12). Briefly, IRAS is a longitudinal, multicenter study of the relationships among insulin, insulin resistance, cardio- vascular disease, and its risk factors in in- dividuals with a broad range of glucose tolerance. The baseline examination for IRAS (exam 1) was conducted from Octo- ber 1992 to April 1994. A total of 1,625 ●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●● From the 1 Department of Epidemiology and Biostatistics, Norman J. Arnold School of Public Health, University of South Carolina, Columbia, South Carolina; the 2 PHS Core Laboratory, Fred Hutchinson Cancer Research Center, Seattle, Washington; and the 3 Department of Public Health Sciences, Wake Forest University School of Medicine, Winston-Salem, North Carolina. Address correspondence and reprint requests to Elizabeth J. Mayer-Davis, PhD, Department of Epidemi- ology and Biostatistics, Norman J. Arnold School of Public Health, University of South Carolina, Columbia, SC 29208. E-mail: mayer@gmw.sc.edu. Received for publication 27 June 2002 and accepted in revised form 13 September 2002. Abbreviations: -TE, -tocopherol equivalents; FFQ, food frequency questionnaire; IGT, impaired glucose tolerance; IRAS, Insulin Resistance and Atherosclerosis Study; OR, odds ratio. A table elsewhere in this issue shows conventional and Syste `me International (SI) units and conversion factors for many substances. Clinical Care/Education/Nutrition O R I G I N A L A R T I C L E 2172 DIABETES CARE, VOLUME 25, NUMBER 12, DECEMBER 2002 Downloaded from http://diabetesjournals.org/care/article-pdf/25/12/2172/646486/dc1202002172.pdf by guest on 17 July 2022