The Hidden Health Metric That Matters Most: Your Circadian Rhythm
Have you ever noticed how you feel alert and energetic at certain times of day and drowsy at others? It’s not random—it’s your circadian rhythms at work.
Centuries ago, a French astronomer placed a plant in total darkness and observed something remarkable: it continued to open and close its leaves on a 24-hour cycle. The conclusion? Living things aren’t just reacting to the world around them—they’re tracking time internally.
That experiment marked the birth of circadian biology, and the science has exploded since. Today, we know that nearly every one of your ~37 trillion cells runs on a schedule.
In humans, this internal timing system is controlled by a “master clock” in the brain—a bundle of neurons called the suprachiasmatic nucleus (SCN)¹ . Each morning, when light enters your eyes, it activates a specific type of cell in the retina called intrinsically photosensitive retinal ganglion cells (iPRGCs). These cells help your body determine what time it is and reset your internal clock accordingly.
This internal timing system is the conductor of a daily symphony, orchestrating countless biological functions so they operate at the right time. It primes your body for restorative sleep, boosts immune activity during the day when exposure to pathogens is higher, prepares your digestive system for meals, and even ramps up skin protection when the sun is highest in the sky.
But all this hinges on one critical factor: your body knowing what ‘time’ it is. When your internal clock is misaligned, it might prepare you to run a marathon when it should be winding you down for sleep. This mismatch isn’t just disruptive in the moment, it causes biological confusion at the cellular level that, over time, accumulates into real damage. This mismatch has been linked to chronic diseases ranging from cancer to dementia.²
And yet, we don’t track our internal time. We don’t prioritize it. We barely even talk about it.
Let’s start talking about it.
Dr. Jonathan Moustakis
Co-founder and CTO of Lume Health
¹ Sanchez, R.E.A., Kalume, F., & de la Iglesia, H.O. (2022). Sleep timing and the circadian clock in mammals: Past, present and the road ahead. Seminars in Cell & Developmental Biology. Link
² Fishbein, A.B., Knutson, K.L., & Zee, P.C. (2021). Circadian disruption and human health. Journal of Clinical Investigation, 131(19): e148286. Link
