Racial variation in insulin-like growth factor-1 and binding protein-3 concentrations in middle-aged men

African-American men have the highest and Asian-American men have the lowes t prostate cancer incidence rates in the United States; internationally, ra tes for the Asian continent are among the lowest. Higher insulin-like growt h factor (IGF)-1, which participates in the control of cellular growth and differentiation and is modulated by IGF-binding protein-3 (IGFBP-3), was as sociated with an increased prostate cancer risk in three recent studies. We , therefore, investigated whether plasma levels of IGF-1 and IGFBP-3 vary b y race in United States men selected from among members of the Health Profe ssionals Follow-up Study who were 47-78 years old in 1993-1995 when they pr ovided blood (n = 18,000). All of the men who described their major ancestr y as African American (n = 63) and a random sample of 75 Asians and 75 Cauc asians were invited to provide a second blood sample in 1997, of whom 42, 5 2, and 55, respectively, did so. IGF-1 and IGFBP-3 concentrations were dete rmined by ELISA, We used nonparametric methods to assess racial variation i n age-adjusted levels. Caucasians had the highest median IGF-1 level (224 n g/ml), followed by Asians (208 ng/ml) and African Americans (205 ng/ml), Me dian IGFBP-3 concentration was similar between Caucasians and Asians but wa s more than 13% lower in African Americans. Median molar IGF-1:IGFBP-3 rati o was greatest in Caucasians and lowest in Asians. The lower IGF-1 blood le vels relative to IGFBP-3 levels among Asian men are consistent with their l ower prostate cancer incidence. Although differences in circulating IGF-1 d o not seem to account for the greater prostate cancer risk among African-Am erican men, their absolute lower levels of IGFBP-3 may be contributory.