Recent reports have indicated that SIRT1 can be detected in the serum of patients with various pathologies, such as fatty liver disease,37 obesity,18 chronic obstructive pulmonary disease (COPD)38 and Alzheimer’s disease.39 Specifically, the serum level of SIRT1 declines in patients suffering from frailty (sarcopenia; cognitive decline; abnormal immune function and neuroendocrine systems; and poor energy regulation,40), COPD, metabolic instability and Alzheimer’s disease. Here, SIRT1 is linked to Alzheimer disease.