Essentials: Timing Light for Better Sleep, Energy & Mood | Dr. Samer Hattar

Dr. Samer Hattar and Andrew Huberman examine the critical influence of light on circadian rhythms and the potential for misalignment due to modern light environments.

Morning Light Synchronizes the Body's Internal Clock to the 24-hour Cycle

Morning Sunlight Resets Circadian Rhythm

Hattar discusses the inherent circadian clock in humans which, left without external cues, maintains a rhythm not entirely aligned with a 24-hour cycle. Morning sunlight is crucial because it resets this rhythm to match the 24-hour solar day. Huberman recommends 10 to 30 minutes of morning light exposure daily to regularize the circadian rhythm. Without this exposure, people might find their rhythms drifting later and later, leading to misalignment.

Light Disruption Desynchronizes Body's Clock

Clock-Cycle Mismatch Can Cause Sleep, Mood, and Metabolic Issues

Hattar cites a subset of retinal cells, intrinsically photosensitive ganglion cells, which are pivotal for synchronizing our internal clocks with the natural light-dark cycle. Even some blind individuals with these cells intact can entrain to this cycle despite lacking image perception. Hattar and Huberman note how modern lifestyles with indoor living and late-night artificial lighting can cause shifts in the body’s clock, leading to a host of issues such as sleep disturbances, mood changes, and metabolic problems. They mention that a disruption in this cycle can fragment sleep, reduce focus, and decrease alertness.

Indoor or Excessive Night Lighting Causes "Social Jet Lag," Misaligning Internal Clock With Natural Light-Dark Cycle

Late sleep and wake times can increase depression, as they lead to missing the beneficial effects of morning sunlight. Hattar also raises the concept of "social jet lag," where inappropriate light exposure, such as bright lights at night, leads to a desynchronized sleep-wake cycle. This misalignment with the sunrise causes difficulty in sleeping at conventional times.

Moreover, th ...

Light Impacts Mood and Emotion, Separate From Internal Clock Effects

Samer Hattar and Andrew Huberman discuss how light exposure directly influences mood and learning, separate from its known role in regulating circadian rhythms.

Photoreceptor-Input Brain Regions Entrain Circadian System, Modulating Mood and Cognition

Hattar explains that light affects functions in the body independently of conscious vision, like setting the circadian clock, which also impacts mood. Furthermore, he clarifies that light also has direct effects on mood and cognition separate from its effects on the circadian system. This suggests that regions of the brain that control mood receive direct input from intrinsically photosensitive retinal ganglion cells (IPRGCs), which are different from areas associated with the circadian clock. This mood-regulating region projects to brain areas known to control mood, including the ventral medial prefrontal cortex, implicated in human depression. The discussion indicates that disrupting light exposure or changing its timing has dramatic effects on the stress system and learning and memory systems, making us feel happier or stressed, depressed, energetic, or even manic.

Light Influences Appetite, Hunger, and Feeding Behaviors

The effect of light on appetite, feeding behaviors, and possibly metabolism is brought up by Andrew Huberman, based on Samer Hattar's research findings.

Light and Meal Timing Optimize Appetite and Metabolism

Hattar shares a personal experience where adjusting his light exposure an ...

Optimal light exposure can be key in improving sleep, mood, and overall health. Both Samer Hattar and Huberman share insights into how managing light can entrain our body's internal clock, impacting our circadian rhythm and well-being.

Establish a Consistent Morning Light Exposure Routine

Getting morning light is essential for setting the body's internal clock and adapting to the natural day-night cycle.

Get 15-30 Minutes of Bright Light Soon After Waking

Hattar recommends 15 minutes of light exposure daily to adjust to the day-night rhythm. Even on cloudy days or in the shade, the intensity is sufficient for circadian entrainment. Huberman suggests getting 15 to 30 minutes of bright light upon waking to align the internal clock with the natural light-dark cycle, reinforcing the idea that a routine of light exposure can profoundly influence our circadian rhythm.

Aligns Internal Clock with 24-hour Light-Dark Cycle

The body is primed to receive light upon waking when already entrained, which assists in synchronizing the internal clock with the natural day-night cycle. Hattar notes the importance of this alignment, especially when traveling across time zones, as it can shift the internal clock to match the local time, further illustrating the relationship between light exposure and the 24-hour cycle. Likewise, getting into a consistent rhythm with light exposure is vital as it can be challenging to break a sleep-wake cycle once established.

Minimize Evening/Nighttime Light Exposure

To prevent disrupting the circadian rhythm, evening and nighttime light exposure should be managed carefully.

Limit Evening Exposure to Bright Lights, Screens, and Blue Light to Boost Melatonin and Aid Sleep

Hattar warns against the negative impact of using very bright light at night, which can disrupt sleep cycles. Huberman recommends red lens glasses after sunset to filter out short-wavelength light that suppresses melatonin and increases cortisol, ultimately promoting relaxation and aiding the transition to sleep.

Use Dim, Red-shifted Lighting at Night to Minimize Circadian Disruption

Hattar suggests keeping home lighting dim in the evening and using very dim red light in sleeping areas, which hardly affects the circadian clock. He emphasizes that below 10 lux, red light does not significantly impact sleep, indicating that dimmer, red-shifted light is preferable for aligning with ...