Insulin sensitivity and intake of vitamins E and C in African American, Hispanic, and non-Hispanic white men and women: the Insulin Resistance and Atherosclerosis Study (IRAS)

Abstract

Elevated fasting insulin concentrations and insulin resistance have been associated with non-insulin-dependent diabetes mellitus (NIDDM), obesity, atherosclerosis, and hypertension. Vitamin E supplementation in persons with and without NIDDM may be related to greater insulin sensitivity (SI). The cross-sectional associations of the intake of vitamins E and C with SI and insulin concentrations were evaluated among African American, Hispanic, and non-Hispanic white men and women with a wide spectrum of glucose tolerance included in the Insulin Resistance and Atherosclerosis Study (IRAS) (n = 1151). Insulin sensitivity was measured by minimal model analysis of a 12-sample, insulin-modified, frequently sampled intravenous glucose tolerance test. Nutrient intake (including vitamin supplement use) was assessed with a food-frequency questionnaire modified to include foods consumed by the three ethnic groups. Linear-regression models were used, including rank of SI and the log of fasting insulin as the outcome variables. Pearson correlation coefficients for vitamins E and C in relation to rank SI were r = 0.07 (P = 0.01) and r = 0.07 (P = 0.02), respectively. After adjustment for total energy and BMI these associations were no longer statistically significant and did not differ between ethnic groups. Results were similar when vitamins E and C were combined in categories of low and high antioxidant intake. Models replicated with log of fasting insulin as the outcome variable also did not produce significant associations with vitamins E or C. Thus, these cross-sectional analyses do not support the hypothesis of improved SI with increased intake of vitamins E and C.

The Metabolic Syndrome and Antioxidant Concentrations

“…Increased free radical production has been shown to correlate inversely with insulin action (43). Although several studies have shown inverse associations between measures of insulin resistance and antioxidant concentrations (44) and improvements in insulin action with antioxidant supplementation (45), not all studies have shown such associations (46). Of note is that people with the metabolic syndrome have a high prevalence of insulin resistance, which is associated with an increased risk of developing diabetes.…”

Food consumption and the incidence of type II diabetes mellitus

“…In several epidemiological studies, intakes or serum levels of vitamin C, vitamin E, or carotenoids have been inversely associated with diabetes (Chatterjee & Banerjee, 1979;Sinclair et al, 1994;Feskens et al, 1995;Salonen et al, 1995;Abahusain et al, 1999;Ford et al, 1999;Knekt et al, 1999;Will et al, 1999;Polidori et al, 2000;Montonen et al, 2004b). However, the findings on the relation between antioxidants and glucose metabolism are not consistent (Sanchez-Lugo et al, 1997;Reunanen et al, 1998;Liu et al, 1999). Moreover, flavonoids may provide protection against chronic diseases by their free radical scavenging properties.…”

Dietary Antioxidant Intake and Risk of Type 2 Diabetes

“…Two crosssectional studies have failed to show a relation between ␤-carotene and glycated hemoglobin (29,30). Analyses from the Insulin Resistance and Atherosclerosis Study did not show a significant association between insulin sensitivity and intakes of vitamin E and C (33). In clinical experiments, pharmacological doses of vitamin E have improved the insulinmediated glucose uptake (34,35).…”