IGF1 and Alzheimer disease: Obesity is associated with AD [6], and increased insulin resistance (IR) is also associated with AD independently [7], as insulin is able to freely cross the blood brain barrier [7], and it has been suggested that the underlying molecular mechanisms of IR and AD are due to insulin receptor substrate 1 (IRS-1) and insulin-like growth factor 1 (IGF-1) receptor dysregulation [8].