Alzheimer's disease (AD) is a progressive brain disorder that causes memory and thinking problems. The exact cause of AD is unknown. Researchers believe mitochondria (the part of your cells that produce energy) might be linked to symptoms of AD. Some studies have shown that the brains in patients with Alzheimer's disease have reduced mitochondrial activity, have fewer mitochondria present in the nerve cells, and have reduced ability to utilize glucose (sugar) for energy.