Ethnic Disparity in the Relationship between Obesity and Plasma Insulin-Like Growth Factors: The Multiethnic Cohort

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Abstract
Previous studies on the relationship between obesity and circulating insulin-like growth factor (IGF) hormones show inconsistent findings and have not considered the possibility of racial/ethnic–specific differences that may exist. We therefore examined the relationship between obesity status [as measured by body mass index (BMI)] and plasma levels of the IGF proteins, IGF-I, IGF-binding protein 3 (IGFBP-3), and the molar ratio of IGF-I/IGFBP-3 in Whites, African Americans, Latinos, Japanese Americans, and Native Hawaiians from the ongoing Hawaii and Los Angeles Multiethnic Cohort Study. We measured plasma IGF-I and IGFBP-3 by ELISA in a random sample of 811 Multiethnic Cohort participants (53% male, age range = 47-82 at blood draw). In a multivariate regression of IGF-I levels, we found a statistically significant interaction between race/ethnicity and obesity status (P = 0.005). Plasma IGF-I levels declined with increasing BMI most dramatically in Latinos and Japanese. This decline was attenuated in Whites and absent in African-American and Native Hawaiian subjects. In Japanese, the quadratic term (BMI2) was statistically significant in a multivariate model (P = 0.002). In Latinos, the adjusted least-squares mean IGF-I levels in ng/mL for BMI < 25, 25 to 29.99, and ≥30 were 184.6, 147.7, and 132.7, respectively. No interaction between race/ethnicity and BMI explained the plasma IGFBP-3 levels in these data. These results may help to resolve the uncertainty in the relationship between circulating IGF levels and obesity and highlight the potential importance of racial/ethnic–specific effects among these factors in explaining ethnic disparities in obesity-related cancers. (Cancer Epidemiol Biomarkers Prev 2006;15(11):2298–302)

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