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J Fowke, Division of Epidemiology, Vanderbilt University Medical Center, Nashville, United States
C Matthews, Division of Epidemiology, Vanderbilt University Medical Center, Nashville, United States
H Yu, Yale University, New Haven, United States
Q Cai, Division of Epidemiology, Vanderbilt University Medical Center, Nashville, United States
S Cohen, International Epidemiology Institute, Rockville, United States
M Buchowski, Division of Gastroenterology, Heptaology, and Nutrition, Vanderbilt University Medical Center, Nashville, United States
W Zheng, Division of Epidemiology, Vanderbilt University Medical Center, Nashville, United States
W Blot, International Epidemiology Institute, Rockville, United States

Jay Fowke, Email: jay.fowke{at}vanderbilt.edu

Abstract

African American (AA) race/ethnicity, lower body mass index (BMI), and higher insulin-like growth factor 1 (IGF-1) levels are associated with premenopausal breast cancer risk. This cross-sectional analysis investigated whether BMI or BMI at age 21 years contribute to racial differences in IGF-1, IGF-2, IGFBP-3, or free IGF-1. Participants included 816 white and 821 AA women between ages 40 and 79 years across a wide BMI range (18.5-40 kg/m2). Compared with white women, AA women had higher mean IGF-1 (146.3 vs. 134.4 ng/ml) and free IGF-1 (0.145 vs. 0.127) levels, and lower IGF-2 (1633.0 vs. 1769.3 ng/ml) and IGFBP-3 (3663.3 vs. 3842.5 ng/ml) levels (all p<0.01; adjusted for age, height, BMI, BMI at age 21, and menopause status). Regardless of race, IGF-1 and free IGF-1 levels sharply rose as BMI increased to 22-24 kg/m2, then declined thereafter, while IGF-2 and IGFBP-3 levels tended to rise with BMI. In contrast, BMI at age 21 was inversely associated with all IGF levels, but only among white women (p-interaction = 0.01). With the decline in IGF-1 with BMI at age 21 among whites, racial differences in IGF-1 significantly increased among women who were obese in early adulthood. In summary, BMI was associated with IGF-1 levels regardless of race/ethnicity, while obesity during childhood or young adulthood may have a greater impact on IGF-1 levels among white women. The effects of obesity throughout life on the IGF axis and racial differences in breast cancer risk require study.