Timing Your Light, Food, & Exercise for Optimal Sleep, Energy & Mood | Dr. Samer Hattar
Dr. Samer Hattar, Ph.D., an expert on light and circadian rhythms, discusses how light exposure at specific times impacts mood, learning, and appetite. He offers precise tools to align sleep-wake cycles, food intake, and exercise for optimal mental and physical functioning, and to adjust to jet lag or shift work.
Deep Dive Analysis
20 Topic Outline
Introduction to Dr. Samer Hattar and Light's Impact
Circadian and Circannual Photoentrainment
Discovery of Intrinsically Photosensitive Retinal Ganglion Cells (IPRGCs)
Subconscious Light Detection in Blind Individuals
Optimal Morning Light Viewing for Circadian Alignment
Light Intensity, Duration, and Cloud Cover Considerations
The Concept of 'Light Hunger' and Daytime Light Exposure
Evening Light, Blue Blockers, and Dimming Strategies
Dangers of Bright Light at Night on Mood and Learning
The Tripartite Model: Circadian, Sleep Drive, and Environmental Input
Direct Effects of Light on Mood and the Hattar-Hernandez Nucleus
The Function of Sleep and Non-Sleep Deep Rest
Light's Impact on Appetite and Timing of Meals
Dr. Hattar's Personal Protocol for Aligning Sleep, Food, and Exercise
Age-Related Changes in Vigor and Chrono-Attraction
Rapidly Resetting Your Clock After Late Nights or Travel
The Importance of Clock Gene mRNAs as Biomarkers
Light as Medicine for Mood and Attention Deficit
Seasonal Rhythms, Mood, and the Impact of Daylight Savings
Individual Differences in Light Sensitivity and Eye Color
8 Key Concepts
Circadian Clock
An internal biological rhythm that approximates a 24-hour cycle, even in constant conditions. It governs sleep-wake cycles, cellular functions, and behavior, and needs external cues like light to precisely align with the solar day.
Circadian Photoentrainment
The process by which the body's internal circadian clock is adjusted or 'trained' to the external light-dark environment. This process is largely subconscious and independent of conscious vision.
Intrinsically Photosensitive Retinal Ganglion Cells (IPRGCs)
A small subset of neurons in the eye that are themselves photoreceptors, containing the photopigment melanopsin. These cells are responsible for detecting light and relaying subconscious light information directly to brain regions that regulate circadian rhythms, mood, and other non-visual functions.
Melanopsin
The photopigment found within IPRGCs, first discovered in frog melanocytes (skin cells). It converts light energy into electrical signals that communicate day-night information to the brain, playing a crucial role in setting the circadian clock.
Light Hunger
A hypothesized biological need in animals, including humans, to measure and receive light exposure throughout the day. This 'hunger' for light may relate to anticipating seasonal changes and ensuring survival by aligning physiological processes with environmental cues.
Tripartite Model
A comprehensive model proposing that human physiological functions, such as sleep-wake cycles and feeding, are regulated by three interacting components: the circadian clock, the homeostatic drive (e.g., sleep debt), and direct environmental inputs like light, stress, and food availability. All three must be considered together for optimal health.
Hattar-Hernandez Nucleus (Peri-habenula)
A brain region, specifically the peri-habenula, that receives direct light input from IPRGCs and projects to areas known to regulate mood, including the prefrontal cortex. This pathway demonstrates that light can directly affect mood independent of its effects on the circadian clock or sleep.
Chrono-Attraction
A hypothesis suggesting that individuals who attract each other, particularly in relationships with children, often have different sleep-wake schedules (chronotypes). This distribution of sleep times across a 24-hour cycle could serve an evolutionary purpose, allowing for continuous care and protection of offspring.
9 Questions Answered
Light impacts these functions through its effect on the circadian clock, but also through direct, subconscious pathways to specific brain regions that regulate mood and learning, independent of sleep. It also influences appetite and feeding behavior by interacting with the body's internal timing systems.
These are a small subset of retinal ganglion cells, now called Intrinsically Photosensitive Retinal Ganglion Cells (IPRGCs), which contain the photopigment melanopsin. They detect light and send signals to the brain's central circadian pacemaker, the suprachiasmatic nucleus (SCN), without contributing to conscious vision.
Aim for 10-15 minutes of outdoor light exposure daily, ideally within an hour of waking. If it's cloudy, stay outside longer (e.g., 30-45 minutes). This helps entrain your circadian clock, and even on overcast days, outdoor light is significantly brighter than indoor light.
Dr. Hattar personally does not recommend blue light blockers because they distort vision by removing a single wavelength from the full light spectrum. Instead, he suggests dimming all lights at night and adjusting the color temperature of artificial lights to reduce blue content without eliminating it, maintaining a full spectrum white light.
Bright light exposure during these hours, even without disrupting the circadian clock or causing sleep deprivation, can lead to significant negative impacts on mood and learning ability. This is due to direct light pathways to specific brain regions involved in these functions.
Light viewing and feeding behavior interact to support one another, influencing hunger and energy levels. Regular meal times, especially during your active phase, act as another signal to your body's clock, helping to regulate hunger cues and improve metabolic health.
To advance your clock (e.g., traveling east), view bright light after your body's temperature nadir (lowest point), typically around 5 AM for a 7 AM wake-up. To delay your clock (e.g., traveling west), view light in your early evening. Additionally, eating on the local schedule can help, but avoid light at the 'wrong' times relative to your body's internal clock.
It is plausible that people with lighter eye colors are more sensitive to light because their pupils block less light compared to darker pigmented eyes. This means they might perceive bright conditions as more intense and require less light exposure to achieve the same biological effects.
Daylight Savings Time disrupts the natural, consistent rhythm of light exposure that the body relies on for circadian alignment. The one-hour shift, especially in spring, pushes people to get later light exposure, compounding existing circadian disruptions and negatively impacting mood, sleep, and overall health, rather than smoothly transitioning with the seasons.
14 Actionable Insights
1. Optimize Morning Light Exposure
Expose your eyes to as much outdoor light as possible for 15-60 minutes immediately upon waking, even on cloudy days, and without sunglasses, to set your circadian clock, prime your system, and improve mood. If waking before sunrise, use a bright artificial light source until the sun is out, then transition to outdoor sunlight.
2. Minimize Evening/Night Light Exposure
Significantly dim all artificial lights in your home at night, aiming for the minimum comfortable level, and allow 10-15 minutes for your eyes to adapt to darkness. Avoid bright screens (phones, tablets) 1.5-2 hours before bed, or dim them to the lowest setting and view indirectly if necessary, as light at the wrong time can disrupt sleep and mood.
3. Embrace Daytime Bright Light
Seek abundant bright light exposure throughout the day, beyond just the morning, to satisfy a ’light hunger’ and directly enhance mood, learning, memory, and alertness, even if your circadian clock is already set.
4. Align Meal Times with Circadian Rhythm
Establish regular meal times that align with your active circadian phase and light exposure, as consistent feeding acts as a strong signal to entrain your body’s clock, regulate hunger, and support overall health. Restrict your eating window to the active phase of your circadian cycle, avoiding food intake during your body’s designated resting period.
5. Strategize Exercise Timing
Identify your optimal sleep-wake cycle and schedule exercise during your most alert period, as aligning physical activity with your natural rhythm can enhance performance and prevent sleep disruption from elevated body temperature or light exposure.
6. Utilize the Tripartite Model for Health
Adopt a holistic approach to health by considering the interplay of your circadian clock, homeostatic drives (e.g., sleep debt), and direct environmental inputs (e.g., light, stress) to optimize sleep, mood, and overall well-being.
7. Adjust to New Schedules with Light Timing
To shift your circadian clock (e.g., for travel or new routines), view bright light in the early evening to delay your clock (e.g., traveling west), or view bright light after your body’s temperature nadir (low point, typically late night/early morning) to advance your clock (e.g., traveling east). When arriving in a new time zone, avoid bright light if it’s your body’s subjective night/early morning in the new location, as this could further delay your clock instead of advancing it.
8. Evaluate Light Needs with Self-Experimentation
Do not rely solely on conscious perception for light intensity; instead, conduct simple experiments by dimming lights and allowing 10-15 minutes for eye adaptation to discover the minimum comfortable light level you truly need at night.
9. Ensure Optimal Hydration and Electrolytes
Prioritize proper hydration and adequate electrolyte intake (sodium, magnesium, potassium) for optimal brain and body function, as even slight dehydration can diminish cognitive and physical performance. Drink an electrolyte mix (like Element) first thing in the morning and during physical exercise.
10. Practice Non-Sleep Deep Rest (NSDR)
Incorporate 10-minute sessions of Yoga Nidra or Non-Sleep Deep Rest (NSDR) into your routine to significantly restore cognitive and physical energy, especially when full sleep is not possible.
11. Avoid Blue Blockers for General Use
Refrain from using blue-blocking glasses that distort the full light spectrum, as they may not effectively prevent circadian disruption if overall light intensity is high, and can negatively impact vision. Instead, adjust the spectrum of artificial lights to be warmer (less blue, more yellow) in the evening while maintaining a white appearance.
12. Minimize Light During Nighttime Awakenings
If you wake up in the middle of the night (e.g., for a bathroom break), avoid turning on bright lights or using screens to prevent sending an alerting signal to your brain, which could disrupt your ability to fall back asleep.
13. Realign After Occasional Schedule Disruptions
Do not worry excessively about occasional disruptions to your sleep-wake schedule (e.g., late nights); instead, prioritize quickly readjusting to your optimal light, eating, and exercise routine to prevent chronic misalignment.
14. Advocate Against Daylight Saving Time
Support efforts to abolish daylight saving time, as its abrupt shifts disrupt natural circadian rhythms, negatively impact health, and compound existing issues related to light exposure misalignment.
11 Key Quotes
So the sunlight adjusts that approximate day to an exact day.
Dr. Samer Hattar
So you're literally one hour off in your social behavior in five days. In 10 days, you're two hours off. And if you're an organism that is living in the wild, shifting out of the right phase of the cycle, you could either miss food or you could become food.
Dr. Samer Hattar
So honestly, David, person say you have a fly in your eye because it sounds better. The more accurate, I think, is that you have a frog skin in your eye.
Dr. Samer Hattar
The cloudiest day is going to be much more brighter than your room.
Dr. Samer Hattar
So you have to teach people how to understand intensity and that's something that you have to explain to people.
Dr. Samer Hattar
I think there is a weird light hunger, considering that we're not photosynthetic organisms. There is a weird light hunger in animals that they need to measure.
Dr. Samer Hattar
I personally do not like any blockers that take a single wavelength of light because, again, if you think of a holistic approach, yes, the blue blocker is going to prevent you from affecting your circadian clock very much, but then your vision is going to be distorted because we always see in full spectrum.
Dr. Samer Hattar
I don't like to make it completely dark. I think complete darkness induce anxiety in humans, to be honest.
Dr. Samer Hattar
I say don't take a pill, take a photon.
Dr. Samer Hattar
medicine I think still now we are very good at looking at stuff spatially but we're very bad at looking at temporal aspects.
Dr. Samer Hattar
Daylight saving, it's such a bad idea because it disrupts that rhythm that you're having.
Dr. Samer Hattar
3 Protocols
Minimal Light Test for Nighttime Environment
Dr. Samer Hattar- Place three to four lights in your room.
- Switch off two of the lights.
- Sit for 15 minutes, allowing your eyes to adapt to the dimmer conditions.
- Observe that you will likely not recognize that two lights were switched off, indicating you need less light than you think to see comfortably.
Adjusting Sleep-Wake Schedule for Travel or Shift Changes
Dr. Samer Hattar- Identify your desired new wake-up time.
- Determine your body's temperature nadir (lowest point), which is typically about 2 hours before your usual wake-up time.
- To advance your clock (e.g., traveling east or shifting to an earlier schedule), view bright light shortly after your temperature nadir (e.g., 5 AM for a 7 AM wake-up).
- To delay your clock (e.g., traveling west or shifting to a later schedule), view bright light in your early evening.
- Once at the new location or on the new schedule, eat meals according to the local time to provide additional cues to your body's clock.
- Avoid bright light at times that would shift your clock in the undesired direction (e.g., avoid Italian sunrise if you just flew from New York and didn't pre-shift).
Dr. Hattar's Personal Protocol for Optimal Vigor and Health
Dr. Samer Hattar- Dim lights significantly at night, using minimal light (e.g., candlelight or very dim red light) to see comfortably.
- Maintain a consistent sleep schedule, going to bed around 9 PM and waking between 4:30 AM and 5 AM.
- Consume the largest meals during the active and hungry periods of the day, such as a big breakfast around 7 AM and lunch between noon and 1 PM.
- Limit or avoid dinner, especially after 3 PM, as the body's system naturally ramps down.
- Exercise in the morning, as this aligns best with the body's natural vigor and does not disrupt sleep later.
- Keep office windows completely open and seek bright light exposure throughout the day to feed 'light hunger' and support mood and learning.