A study involving mice lacking a master clock gene called Bmal1 has found that as the mice aged, their brains showed patterns of damage similar to those seen in Alzheimer's disease and other neurodegenerative disorders. Many of the injuries seemed to be caused by free radicals. Several key antioxidant enzymes, which usually neutralize and help clear free radicals from the brain, have been found to peak in the middle of the day in healthy mice, but not in these mice lacking Bmal1. It may be that, without this daily increase, free radicals remain in the brain longer, causing more damage.
The finding may help explain the connection between sleep problems and Alzheimer’s.
 Circadian clock proteins regulate neuronal redox homeostasis and neurodegeneration. Journal of Clinical Investigation. 123(12), 5389 - 5400.(2013).