Utility of Insulin-like Growth Factor-1 as a Biomarker in Epidemiologic Studies

Abstract

Recent studies have correlated high serum insulin-like growth factor-1 (IGF-1) with increased risk of several common cancers, primarily prostate, breast, colorectum, and lung (1)(2)(3); low concentrations of circulating IGF-1 have been associated with osteoporosis (4), impaired cognitive function (5), and heart disease (6). IGF-1 screening may help prevent chronic disease by identifying high-risk individuals (7)(8). Although normal adult IGF-1 concentrations relative to age and sex have been widely reported, based on cross-sectional data (9)(10)(11)(12)(13)(14), there have been few longitudinal studies. Most studies measuring multiple samples followed only a few individuals over short periods (15)(16)(17)(18)(19). Knowing the degree of individual variation over longer time periods would be useful (20). Staff volunteers gave informed consent for the study. Blood was drawn monthly between 0800 and 1000 in the morning from 26 apparently healthy adults, and medications and time of last meal were recorded. Within 1 h of collection, samples were centrifuged, and serum was stored at −20 °C until analysis, which was within 1 month of collection. Serum IGF-1 was measured in 13 men (starting ages, 24–77 years; median, 49 years) and 13 women (starting ages, 23–56 years; median, 41 years). The total number of samples from each individual varied from 13 to 56 (mean, 31), and they were collected over 1.2–6 years (mean, 4.5 years). Use of previously collected serum stored at −40 °C extended the time period followed for two male volunteers to 16 years. In addition, multiple aliquots from three male volunteers (ages, 26, 44, and 75 years) used for assessing interassay variability were stored at −20 °C for 1–12 months. IGF-1 concentrations were measured by IRMAs from Diagnostic Systems Laboratories. Samples were extracted …