Abstract 14988: Low Beta-Carotene Levels are Associated with Elevated Insulin and Insulin Resistance in Healthy African American Men and Women

Abstract

Introduction: Lower levels of beta-carotene are associated with increased risk of Type 2 diabetes, glucose intolerance and insulin resistance. Given the higher prevalence of Type 2 diabetes and poor conversion of beta-carotene to retinol in African Americans (AA), it was hypothesized that, relative to Caucasians, AA would exhibit lower beta-carotene levels and lower beta-carotene levels would be associated with insulin resistance in AA. .

Methods: Data were collected on 177 non-smoking, healthy adult men and women (18-65 yrs, 48% women, 33% African American). Fasting blood samples were collected for assessment of beta-carotene, insulin and glucose. Blood samples for premenopausal women were collected during the follicular phase. The Homeostatic model assessment (HOMA) was used to calculate insulin resistance (IR). Multivariate models with age, body mass index, vitamin supplement use, exercise, alcohol intake, education, and total cholesterol as covariates were used to test the interaction between log-transformed beta-carotene and ethnicity. Outcome variables included fasting insulin and glucose and log-transformed HOMA.

Results: Average level of beta-carotene was 21.5 mg/dl. Consistent with previous studies, significantly higher beta-carotene levels were observed in women (p = .008), Caucasians (p = .02) and vitamin supplement users (p < .001). Use of vitamin supplements did not differ by race or gender. Results of multivariate analysis revealed a significant Ethnicity by beta-carotene interaction for HOMA-IR (p = .037) and fasting insulin (p < .001) but not glucose. Among Caucasians, beta-carotene was not associated with HOMA-IR and fasting insulin. In contrast, for African Americans, lower beta-carotene levels were associated with greater HOMA-IR (beta = -0.91, p < .001) and higher fasting insulin (beta = -5.14, p < .001).

Discussion: Independent of potential confounding factors, African Americans exhibited lower beta-carotene levels that were associated with insulin resistance and higher fasting insulin levels, factors associated with increased risk of Type 2 diabetes. These observations may reflect ethnic differences in dietary intake and genetic influences on beta-carotene conversion to retinol in AA.