Light x Little Sleepers: Melanopsin & Circadian Rhythms
“They’re going to sleep so great tonight!”
We’ve all probably heard this before after our kids spend a day engaged in intense outside play: sunshine, running and jumping. They come inside at last, with rosy cheeks and wild hair. We know instinctively that the bright sun influences us and along with the physical activity involved, we anticipate a sound sleep for both ourselves and our children.
Why is this?
What is so special about natural light in the realm of infant/toddler sleep - not to mention our own?
How can we use natural light to support healthy sleep rhythms and maximize our entire family’s innate human drive to experience deep, restorative, healing sleep?
A Surprising “M”-VP
… No, I’m not referring to melatonin, although of course melatonin has a huge role in this process! I’m going to introduce you to another member of the light and sleep team, one you may not have heard of.
Have you ever wondered how your body seems to have a firm grasp on whether to feel sleepy or alert— even without referring to an actual clock? Or why your baby seems more alert during the day and gets fussier as the sun sets? Or, why in the early days and weeks, sleep feels completely all over the place with days and nights seemingly “mixed up”?
Behind the scenes, the eyes are doing so much more than observing the world and making you fall in love with those sparkly depths. Hidden deep within the structure of your baby’s eyes are specialized, light-sensitive cells that help their brain learn the difference between day and night. These cells are called intrinsically photosensitive retinal ganglion cells, or ipRGCs. ipRGCs receive input from a unique light-sensing protein called melanopsin. They play a integral role in developing the sleep-wake cycle- also known as homeostatic sleep drive or circadian rhythm, which is the “internal clock” which helps guide when we sleep and wake. ipRGCs and melanopsin help the brain know whether it’s day or night, which has far-reaching influence: helping regulate everything from sleep to mood to hormone balance. Let’s dive deeper into how this incredible system operates and how it influences the sleep patterns of yourself and your baby, how homeostatic sleep drive matures over time, and how you can use natural light to gently support better rest.
Circadian Rhythms
At birth, your baby was born with a weak circadian rhythm that was influenced by maternal inputs, such as maternal hormones crossing through the placenta into the baby’s bloodstream. After birth, this rhythm was reinforced with hormones in breastmilk if breastfed.
However, the biological 24 hour “internal clock” that regulates sleep/wake cycles is immature and doesn’t fully develop until 3-4 months. Research has shown that appropriate exposure to light in the postnatal period is absolutely critical for healthy circadian development. This is called circadian entrainment, and it is the process by which the baby’s brain receives signals from the ipRGCs to send input throughout the body to influence circadian rhythms. This is accomplished through various means, including hormone regulation and homeostatic processes like movement and digestion. If the baby does not receive light input to help influence and develop this sleep-wake cycle, it can lead to lifelong circadian rhythm dysfunction.
How Light Shapes Sleep
ipRGCs are designed to be highly sensitive to natural light. In fact, they are positioned within the retina only in very specific regions, which correlate to high functional sensitivity to light entering the lower visual field. This, fascinatingly, correlates to light entering the eye from above. This makes total sense because the light from celestial bodies is entering into the human eye from above, meaning the ipRGC’s are optimized to receive natural light from the sun and moon- the original sources of light for human life.
As ipRGCs are exposed to sunlight, melanopsin sends signals to non-image-forming centers in the brain indicating that it is daytime. This essentially “turns off” melatonin production, adjusts mood, energy and focus for wakefulness and controls pupillary response to light. Based on the timing of this light exposure, melatonin secretion from the pineal gland will turn back on when the natural light fades and the brain is no longer receiving signals that it is daytime from the ipRGCs.
Understanding this process is key to grasping how light affects the development of your baby’s circadian rhythms, and how using light can greatly influence sleep patterns and rhythms.
Supporting Baby’s Internal Clock
Blue light gets a bad rap. But it is blue light coming from the sky that drives our body clock and keeps us alert and awake during the day. The issue arises when we introduce blue light when our melanopsin is decreasing and our melatonin should be increasing, or if we never get the blue light exposure during the day to stimulate our ipRGCs to start the wakefulness cascade.
Prioritize morning/daytime light exposure Take your baby outside as soon as possible in the morning. Open your blinds/windows, weather permitting. Go for walks any time - but especially in the morning sunshine!
Reduce evening light exposure Reduce blue light from screens close to bedtime. Consider spending the last hour or so leading up to bedtime with dim warm light to signal impending sleep and to trigger melatonin production.
Create daily rhythms around light Use light to your advantage to reinforce natural sleep rhythms and sleep-wake cycles! Consider ditching the black-out curtains during the day, but using them at night to create less light stimulation and deeper physiological sleep cueing in the evening. Create rhythm to increase natural light (walks in the sun, picnic lunches, stroller or outside naps, weather permitting). For newborns, this consistent light exposure at appropriate times will help them develop a strong circadian rhythm which will benefit them their whole life.
Avoid bright lighting during the night as much as possible, screens before bedtime, dim environments all day. Be mindful of evening summer sun at bedtime and use room-darkening curtains to simulate dark night for bedtime.
From around birth to 6 weeks old, baby’s sleep rhythms are predominantly random patterns based on stimulation, feeding and homeostatic sleep pressure influencing sleep drive and wakefulness. At around 6 weeks, rhythms begin forming but do not fully mature until 3-6 months. At 3-6 months, depending upon your unique baby, they develop their own more stable sleep-wake cycles, ideally synced up with external light cues.
Setting the Stage
For pregnant mamas- did you know your own circadian clock and sleep/wake cycles play a huge role in that of your baby? By observing rhythms of natural light and darkness, you can directly influence the chronosensitivity of your baby and help set them up for a healthy circadian rhythm down the road. Research has shown that if circadian signals from the mother to the baby in utero are interrupted or altered, such as with light pollution, inappropriate exposure to blue light, etc., this can negatively impact the baby’s circadian clock once birth occurs and the baby’s own intrinsic circadian clock begins to mature. It’s never too early to follow the above sleep/light hygiene recommendations.
Gentle Reminders
You are not doing anything wrong, mama! Take this information as empowerment for the future, and knowledge to support the sleep health of your entire family. Go gently with yourself and your baby, and remember that rhythms take time and your baby is developing as they were designed.
Develop your daily rhythms as just that- let go of strict and high-pressure schedules and instead create a daily rhythm that supports your body’s intrinsic needs and design as well as that of your baby. Don’t fight nature, let it support you!
Need more help? Contact me or set up a virtual sleep consult call today. I’d love to help support you and your family to get better rest and more connection.
xoxo,
Laura
References:
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https://doi.org/10.1126/science.1069609
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https://doi.org/10.1152/physrev.00013.2010
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