October 25, 2021 • 2hr 12min
Dr. Samer Hattar: Timing Your Light, Food, & Exercise for Optimal Sleep, Energy & Mood
Huberman Lab
Key Takeaways
- Light exposure is crucial for regulating our circadian rhythms, mood, appetite, and overall health. Getting bright light exposure early in the day (ideally sunlight) for 10-30 minutes helps set our internal clock.
- Our circadian system is controlled by specialized light-sensitive cells in the retina called intrinsically photosensitive retinal ganglion cells (ipRGCs). These cells communicate light information to brain regions that regulate our internal clock and other functions.
- The timing of light exposure is critical. Bright light in the morning advances our clock, while light in the evening delays it. This is important to consider when traveling across time zones.
- Dr. Hattar recommends dimming lights in the evening and using minimal light at night to align with our natural circadian rhythms. Blue light blocking glasses are not recommended as they distort our color vision.
- Aligning our sleep-wake cycle, light exposure, meal timing, and exercise schedule can optimize our circadian rhythms and overall health. This may look different for "morning larks" vs "night owls".
- The "tripartite model" considers how circadian rhythms, sleep drive, and direct environmental inputs like light all interact to regulate our physiology and behavior.
- Daylight saving time shifts disrupt our circadian rhythms and may have negative health impacts. Dr. Hattar argues for abolishing these time changes.
- Individual differences in light sensitivity likely exist based on factors like eye color, but more research is needed to understand this variation.
Introduction
In this episode, Dr. Andrew Huberman interviews Dr. Samer Hattar, Chief of the Section on Light and Circadian Rhythms at the National Institute of Mental Health. Dr. Hattar is a world-renowned expert on how light exposure impacts our circadian rhythms, mood, appetite, and overall health. The discussion covers the biology of how light regulates our internal clocks, practical tips for optimizing light exposure and circadian rhythms, and cutting-edge research on the interactions between light, sleep, mood, and metabolism.
Topics Discussed
The Biology of Circadian Rhythms and Light (6:41)
Dr. Hattar explains that humans have an internal circadian clock that runs on a roughly 24-hour cycle. This clock needs to be synchronized to the external light-dark cycle daily. Special light-sensitive cells in our eyes called intrinsically photosensitive retinal ganglion cells (ipRGCs) detect light and communicate this information to brain regions that control our circadian rhythms.
- Our internal clock runs slightly longer than 24 hours on average (about 24.2 hours) if not synchronized by light
- ipRGCs were discovered in the early 2000s and are distinct from the rods and cones used for vision
- These cells contain the photopigment melanopsin, which is similar to light-detecting proteins found in frog skin
- Even some blind individuals can still entrain their circadian rhythms if they have functioning ipRGCs
Optimal Light Exposure for Circadian Health (20:15)
Dr. Hattar provides recommendations for optimizing light exposure to regulate circadian rhythms:
- Morning light exposure: Get 10-30 minutes of bright light exposure, ideally sunlight, soon after waking
- Even on cloudy days, outdoor light is much brighter than indoor lighting
- Longer light exposure may be needed on darker days
- Daytime light: Continue to get bright light exposure throughout the day when possible
- Evening/night: Dim lights and minimize bright light exposure, especially from screens
- Use the minimum amount of light needed to see comfortably at night
The Direct Effects of Light on Mood and Cognition (56:03)
Dr. Hattar discusses research showing that light exposure can directly impact mood and cognitive function, independent of its effects on circadian rhythms:
- A brain region called the perihabenular nucleus receives light information and projects to areas involved in mood regulation
- Bright light between 10 pm and 4 am can negatively impact mood and learning
- Getting adequate daytime light exposure may help improve mood and cognitive function
The Tripartite Model: Integrating Circadian Rhythms, Sleep Drive, and Environmental Inputs (1:01:05)
Dr. Hattar introduces his "tripartite model" which considers how three key factors interact to regulate our physiology and behavior:
- Circadian rhythms - our internal ~24 hour clock
- Sleep drive - the homeostatic pressure to sleep that builds up during wakefulness
- Direct environmental inputs - like light exposure, feeding, exercise, etc.
He argues that considering how these three components interact is crucial for understanding and optimizing human health and performance.
Aligning Light Exposure, Sleep, Eating, and Exercise Schedules (1:22:51)
Dr. Hattar emphasizes the importance of aligning our light exposure, sleep-wake cycle, meal timing, and exercise schedule to optimize circadian health:
- Finding your ideal sleep schedule and aligning other behaviors with it is key
- This may look different for "morning larks" vs "night owls"
- Regular meal times that align with your circadian rhythm can help regulate appetite
- Exercise timing should be matched to when you feel most alert and energized
Dealing with Jet Lag and Schedule Shifts (1:43:35)
Dr. Hattar provides tips for adjusting to new time zones or schedule shifts:
- Strategically time light exposure based on the direction of travel
- Avoid light at times that would delay adaptation to the new time zone
- Adjust meal and exercise timing to the new schedule
- Allow yourself to sleep in if adjusting to a later schedule
Daylight Saving Time and Seasonality (1:59:08)
Dr. Hattar argues against daylight saving time changes, explaining that even a 1-hour shift can significantly disrupt our circadian rhythms. He also discusses how humans likely have innate seasonal rhythms that are disrupted by modern lifestyles:
- Daylight saving shifts cause more disruption than most people realize
- Keeping a consistent schedule year-round would better align with our biology
- Humans likely have innate seasonal variations in mood, energy, etc. that are masked by artificial lighting and schedules
Individual Differences in Light Sensitivity (2:05:27)
The discussion touches on potential individual differences in light sensitivity:
- People with lighter colored eyes may be more sensitive to light
- Individuals with bipolar disorder may have altered light sensitivity
- More research is needed to understand and measure individual variation in non-visual light responses
Conclusion
Dr. Hattar's research highlights the profound impact that light exposure has on our circadian rhythms, mood, metabolism, and overall health. By understanding the biology of how light regulates these systems, we can make informed choices about our light exposure and daily schedules to optimize our wellbeing. Key takeaways include getting bright morning light, dimming lights in the evening, and aligning our sleep, eating, and exercise schedules with our individual circadian rhythms. Future research may provide more personalized recommendations based on individual differences in light sensitivity and circadian preferences.
