Race/ethnic variation in serum levels of IGF-I and IGFBP-3 in US adults

Objective: The IGF axis plays a significant role in normal growth and development and variation in IGFs is associated with health outcomes. Past studies report variation in IGF levels among race/ethnic groups known to differ in disease incidence. This paper reports on race/ethnic variation in serum levels of IGF-I and IGF-BP3 in a nationally representative and ethnically diverse sample of US adults. Design: Serum IGF-I and IGFBP-3 levels from the fasting subsamples (n = 6061) of respondents to the US National Health and Nutrition Examination Surgery III (NHANES III) were analyzed using an IGF-I ELISA (Diagnostic Systems Laboratory (DSL 10-5600) and an IGFBP-3 IRMA (DSN 6600). The NHANES is a combined examination and interview survery of a nationally representative sample of US adults. Regression analyses were used to estmiate cross-sectional associations between the IGF axis and demographic variables. Results: In unadjusted analysis, serum IGF-I levels were higher in males than in females, and IGFBP-3 levels were higher in females than in males. Both analytes were lower in older adults. Univariate analyses indicate that serum levels of IGF-I are lower in female Non-Hispanic Whites (NHW) (256 [4,9]) and Hispanies (249 [6.6]) than in Non-Hispanic Blacks (NHB) (281 [4.9]). However, in males, IGF levels in NHWs (287 [3.6]) and NHBs (284 [4.3]) are similar and levels in Mexican Americans are only moderately reduced (265 [3.4]). Notably, NHB's have the highest molar ratio of IGF-I:IGFBP-3 at all ages. After adjustment for age and BMI, gender and race/ethnicity differences persist. Conclusions: These cross-sectional data support exploration of the IGF axis as an explanation for some race/ethnic differences in cancer incidence. Published by Elsevier Ltd.