Light, Rhythms, and Circadian Regulation
Sleep Like a Pro | Week 1
By Dr. David Feuz, DCN, CNS, LDN, BCHN
The first step in supporting quality sleep isn’t actually what you do at night. It’s what you do the moment you wake up and throughout the first part of your day. Your body is a finely tuned machine governed by circadian rhythms, with a 24-hour internal master clock located in the hypothalamus of your brain that acts as the central command overseeing and synchronizing these daily biological cycles. These rhythms are not static, but constantly regulated and "reset" by your daily activities, such as your timing of light exposure, meals, and physical exercise. These internal rhythms dictate nearly every biological process, from the obvious sleep-wake cycle to the timed release of hormones and the natural fluctuation of your core body temperature.
For many individuals, this clock is "de-synchronized" due to years of shift work, deployments, or high-stress environments. When your master clock is off, your hormones, metabolism, and recovery systems don't receive the right signals at the right time. By starting here and realigning your circadian rhythm, you ensure your biology is working with you rather than against you, optimizing the impact of every subsequent habit you build to support sleep, whether that be optimizing your nutrition, hydration, sleep environment, or stress management practices.
Synchronizing Your Internal Clock
Light
Think of your circadian rhythm as a mission-essential timer. Research shows that Morning Blue Light (natural sunlight) is the primary external trigger that anchors this clock (Blume et al., 2019).
When sunlight hits your eyes shortly after waking, it sends a direct signal to the Suprachiasmatic Nucleus (SCN) in your brain. This doesn't just wake you up; it "starts the timer" for your brain to naturally release melatonin (your sleep hormone) roughly 14–16 hours later. Conversely, exposure to bright "cool white" artificial lights or screens late at night tricks the brain into thinking it’s still midday, suppressing melatonin production and delaying your body's transition into deep, restorative sleep (Tähkämö et al., 2019).
Getting outside for 10–15 minutes of sunlight shortly after waking tells your brain the day has officially begun. This is the most powerful tool you have to regulate your sleep-wake cycle.
Exercise
While light is the "master" signal, physical activity serves as a powerful secondary anchor. Every muscle and organ in your body contains its own "peripheral clock," and strategic movement acts as a synchronizing signal for these tissues. Research shows that exercise can be nearly as effective as bright light at regulating your internal clock. Being physically active in the morning or early afternoon helps "advance" your rhythm for an earlier release of melatonin, making it easier to fall asleep (Youngstedt et al., 2019). However, intense physical exertion in the evening, too close to bed can "delay" your clock and artificially elevate your core body temperature and cortisol levels, effectively keeping you in an active state and pushing back your natural sleep time.
By staying active during daylight hours, you align your muscles and metabolism with your brain’s internal clock.
Meal Timing
Finally, the timing of your nutrition acts as a critical metabolic signal. Just as movement speaks to your muscles, the timing of your meals tells your digestive system exactly what time it is. Research shows that people who eat their largest meal late in the evening are significantly more likely to struggle with poor sleep timing and disrupted rhythms (Kim et al., 2024). This creates an internal tug-of-war where your body is forced to focus on digestion when it should be prioritizing deep cellular repair. Furthermore, your digestive efficiency and insulin sensitivity naturally decline in the evening, meaning your body is less capable of regulating blood sugar or processing nutrients effectively late at night. Timing is key and eating too close to bedtime, specifically within a three-hour window, is strongly linked to a drop in overall sleep quality (Al-Jawarneh et al., 2025). Finishing your last meal or heavy snack at least three hours before you plan to sleep helps prevent your metabolic system from working overtime while your brain is trying to rest, ensuring your core body temperature can drop naturally for deep, restorative sleep.
Self-Reflection Quiz
Be honest with your current routine. Do any of these sound like you?
Do you spend most of your morning indoors or in low-light environments?
Do you often perform high-intensity workouts after 18:00 (6:00 PM)?
Are your overhead house lights bright and "cool white" right up until you go to bed?
Is dinner your largest meal of the day?
Do you eat a late dinner or snack before bed?
If you answered ‘yes’ to any of these questions and struggle with sleep, it may indicate a circadian rhythm misalignment.
Understanding the "Why" is the first step, but the "How" happens in the app. This week, we are challenging you to anchor your master clock with targeted daily actions.
Take control of your sleep hygiene over 28 days. By stacking small, repeatable actions, you can help achieve deeper sleep, better energy, and stronger days.
Join Eagles from across the nation, 01 - 28 MAY, as they take on the Eagle Fit: Sleep like a Pro Challenge.
David Feuz, DCN, CNS, LDN, BCHN
As a U.S. Coast Guard veteran with 8 years of experience in search and rescue and maritime security, David knows first-hand how sleep deprivation impacts performance.
Currently, David serves as the Academic Department Chair for Nutrition at Purdue University Global and the Director of Nutrition Education at Holistic Consulting, LLC. He holds multiple board certifications/licenses (Certified Nutrition Specialist, Licensed Dietitian Nutritionist, & Board Certified in Holistic Nutrition), a Doctorate in Clinical Nutrition, and a background in integrative health.
David is excited to help the Team RWB community optimize their health from the cellular level up by mastering the most critical pillar of performance: sleep.
References
Al-Jawarneh, M., Chauhan, S., Csölle, I., & Lohner, S. (2025). The Association of Unhealthy Eating Behaviors with Sleep Quality Outcomes Among University Students: A Cross-Sectional Study. Nutrients, 17(22), 3580. https://doi.org/10.3390/nu17223580
Blume, C., Garbazza, C., & Spitschan, M. (2019). Effects of light on human circadian rhythms, sleep and mood. Somnologie, 23(3), 147–156.https://doi.org/10.1007/s11818-019-00215-x
Kim, N., Conlon, R. K., Farsijani, S., & Hawkins, M. S. (2024). Association Between Chrononutrition Patterns and Multidimensional Sleep Health. Nutrients, 16(21), 3724. https://doi.org/10.3390/nu16213724
Tähkämö, L., Partonen, T., & Pesonen, A. K. (2019). Systematic review of light exposure impact on human circadian rhythm. Chronobiology International, 36(2), 151–170.https://doi.org/10.1080/07420528.2018.1527773
Youngstedt, S. D., Elliott, J. A., & Kripke, D. F. (2019). Human circadian phase–response curve to exercise. The Journal of Physiology, 597(8), 2253–2268. https://doi.org/10.1113/JP276943