In an article printed in the American Academy of Neurology, researchers found that people who have lost a substantial amount of cells in the hippocampus area of the brain are more likely to develop dementia.
They performed a study with 64 Alzheimer's patients, 44 people with mild cognitive impairment, and 34 people with no thinking or memory problems. MRI scans were performed at the beginning of the study and then performed half a year later. During that time 23 people with mild cognitive problems had developed Alzheimer's, along with three of the healthy patients. Researchers measured the whole volume of the brain and the hippocampus area. At the beginning and end of the study they calculated the rank of shrinking in the brain over that time. For the people who did not have dementia at the beginning of the study, those with smaller hippocampal volumes, and higher rates of shrinkage were two to four times as likely to develop dementia as those with larger volumes and a slower rate of atrophy. These findings demonstrate that people with mild cognitive impairment have already experienced atrophy within the hippocampus. In people who already have Alzheimer's disease, the loss of nerve cells is spread throughout the brain.
Alzheimer's disease affects millions of people worldwide with no cure at hand. By 2050 it is projected that this disease will affect 1 in 85 people worldwide.
Here is a short video which discusses the effects of the disease: