Science takes a closer look at how our eyes impact sleep as we age
You have likely heard older friends and relatives complain about having trouble sleeping. This is actually normal with aging. Some people notice that they are getting less hours of sleep and waking up more often even as early as their 20s. As we get older, it’s also common to have a harder time getting back to our normal sleep routine after a disruption.
Circadian rhythms are not just cycles of being awake and asleep. Physiologic changes to core body temperature, hormone secretions, urine production and even behaviors such as awareness and cognition, are all regulated according to our internal circadian clocks. But, what makes our circadian clocks tick, if you will?
Cells in the suprachiasmatic nucleus (SCN) of the hypothalamus region of the brain are responsible for the numerous signals needed to coordinate our circadian rhythms in tissues throughout the human body. They receive sensory information regarding light and dark from the retina of the eye via a glutamate receptor known as N-Methyl-D-aspartate (NMDA). That’s right. A good night’s sleep is in the eye of the beholder!
In a recent study published in the Neurobiology of Aging, researchers investigated the connection in mammals between the eye, the receptor NMDA, the SCN in the brain and their impact on circadian rhythms. The eyes, like the rest of the body, are not immune to aging and may undergo a wide range of changes which affect their function. This obviously can affect our ability to read, perceive depth, and other changes to vision.
Additionally, the NMDA was found to become less effective with age. Reduced sensitivity to light in the eye, coupled with reduced efficiency of the NMDA alters the sensory input to the SCN. Therefore, our circadian rhythms – including sleep – may suffer. Researchers found that even a “modest change” in pupillary light sensitivity was associated with “reduced circadian resetting to light.” If the messages typically sent from our eyes to the brain aren’t getting through as efficiently, a different pattern of signals may result in a different sleep pattern.
The study concluded the disruption of normal circadian rhythms is likely caused in part by the SCN’s reduced ability to receive accurate light/dark information from the eye via the NMDA. This impairs its capacity to set and sustain the normal circadian rhythms, including sleep cycles. This new research may lead to improved treatments for “re-setting” the circadian clock, especially for older individuals.
There are many other factors which may impact sleep, including improper support from mattresses and pillows as well as muscle and joint pain or unhealthy eating habits. A doctor of chiropractic can talk to you about good sleep ergonomics and how holistic chiropractic care could help ease pain and improve your overall health. Call to schedule an appointment with your chiropractor today or find a doctor near you, here.
Biello SM, Bonsall DR, Atkinson LA, Molyneux PC, Harrington ME, Lall GS. Alterations in glutamatergic signaling contribute to the decline of circadian photoentrainment in aged mice. Neurobiology of Aging, Volume 66, June 2018, Pages 75-84.