According to an animal study, disruption in sleep patterns and it's consequent threat to their well-being occurs in mammals because advancing age impairs the ability of the circadian clock to reset itself when exposed to light.
Further, age results in a dramatic reduction in sensitivity to light in the suoprachiasmatic nucleus (SCN), the part of the brain that controls circadian rhythms.
In one SCN pathway studied in mice, a glutamate receptor (NMDA) which is used to transmit light information became less effective in resetting the circadian clock and exhibited a markedly decreased presence as a part of the aging process.
Neurobiol Aging. 2018 Feb 20