Latest research claims that chronic lack of sleep may actually cause the development of Alzheimer's disease.
The reason might have to do with the insomnia raising levels of amyloid beta, a protein found in the brain that has been associated with Alzheimer's disease.

For one study, researchers monitored levels of the protein in the brains of sleep-deprived mice with symptoms of the disease. They found that preventing the mice from sleeping caused a 25% increase in amyloid beta levels, forming damaging plaques in the brain that would further disrupt sleep. The findings will be published tomorrow in the journal Science.

via BBC