N-AD: Orally Administered Nicotinamide Riboside Over Two Years as a Potential Disease Modifying Treatment for Alzheimer's Disease

The goal of this clinical trial is to learn if orally administered nicotinamide riboside works to slow the progression of early Alzheimer disease in adults. It will also learn about the safety of drug nicotinamide riboside. The main questions it aims to answer are: * Does drug nicotinamide riboside slow the progression of Alzheimer disease as measured by the Clinical Dementia Rating scale. * What medical problems do participants have when taking drug nicotinamide riboside? Researchers will compare drug nicotinamide riboside to a placebo (a look-alike substance that contains no drug) to see if nicotinamide riboside works to treat early Alzheimer disease. Participants will: * Take drug nicotinamide ribosie or a placebo every day for 24 months * Visit the clinic once every 26 weeks for checkups and tests