The research was done in mice and found that the glutamate receptor (NMDA), which used to transmit light information, became less effective in resetting the circadian clock during the aging process.
It is unclear how much of this translates to humans and whether this means that older people may need more bright light exposure to reset the circadian clock, which in turn affects sleep onset and quality.
Light entrains the circadian clock to our 24-hour day through melanopsin, a photopigment in the eye that is specialized for communicating circadian information instead of image formation.
Additionally, the eye is known to undergo structural changes with age, which can also impact circadian training. Light information is decoded by a subset of retinal ganglion cells expressing the melanopsin photopigment. Melanopsin is specialized for communicating circadian information.
To learn more how the important role early bright light exposure plays in circadian training, check out my first podcast episode with Dr. Satchin Panda, who discovered melanopsin. You can click on the timeline for the specific time points when we discuss the role bright light plays in resetting the clock.