College of Public Health and Human Sciences

BACKGROUND: Alterations in the insulin-like growth factor-I (IGF-I) system have been proposed as a metabolic link between nutritional factors and cancer risk. AIM OF THE STUDY: This study explored dietary determinants of circulating IGF-I and IGF binding protein-3 (IGFBP-3) levels among premenopausal women from different ethnic groups. METHODS: In a cross-sectional design, 258 women with a mean age of 43 +/- 2.7 years donated blood approximately 5 days after ovulation and completed a validated Food Frequency Questionnaire. The majority of the 97 Caucasian, 96 Asian, and 65 Mixed/Other subjects were born in the US. Serum concentrations of IGF-I and IGFBP-3 were measured by double-antibody ELISA. After creating quartiles for 13 food and 13 nutrient density variables, least-square means of IGF-I, IGFBP-3, and the IGF-I/IGFBP-3 ratio were calculated by quartile, while adjusting for age, ethnicity, body mass index, and year of laboratory analysis. RESULTS: Whereas body mass index and dietary intakes varied significantly by ethnicity, IGF-I, IGFBP-3, and their ratio were similar by group. As the only food, fish showed a suggestive inverse association with IGF-I and the IGF-I/ IGFBP-3 ratio. Dietary fiber and vitamin A were positively related to IGF-I (p = 0.004 and 0.03), zinc with IGFB-3 (p = 0.0008), and iron with the IGF-I/IGFBP-3 ratio (p = 0.048), but the differences between the bottom and top quartile were less than 10%. Total energy, protein, carbohydrates, and total fat intake were not related to any serum measurements. CONCLUSIONS: This study detected no ethnic differences in serum IGF-I, but it showed weak associations with dietary variables that require further investigation.