High IGF-1 levels are correlated with higher levels of lean body mass. Neuroprotective, myelinatory, synaptogenic, and anti-catabolic effects of IGF-1 igtropin are well-documented in human and animal study subjects. Serum IGF-1 levels correlate positively to higher IQ in children. IGF- is manufactured in liver mainly and also in skeletal muscle. A form of IGF-1 known as IGF-1 LR3, when applied from an exogenous source, has been shown to circulate longer and bind to more targets in the body than regular IGF-1.