Many diseases that are common in the elderly such as obesity, sarcopenia, insulin resistance, type 2 diabetes mellitus, hypertension, CHD, Alzheimer’s disease, depression, cancer are all associated with a decrease in the activities of desaturases, enhanced activity of COX-2 and altered expression of LOX enzymes and possibly, decreased activity of 15-PGDH, and a frank deficiency or subclinical deficiency of various co-factors needed for adequate metabolism of EFAs such as vitamins B1, B6, B12, folic acid, and various minerals and trace elements could be the underlying cause for excess of PGE2. The gene discussed is PTGS2; the disease is major depressive disorder.