In our hyper-connected modern world, where we have access to artificial light and food around the clock, we’ve drifted far from our body’s natural rhythms. But what if reconnecting with these internal clocks could be the key to unlocking better health, more energy and even a longer life?
This week's guest is Kristen Holmes, Global Head of Human Performance and Principal Scientist at WHOOP, a Science Advisor to Levels Health and Arena Labs, and a member of the Tactical Leadership Board of Sports Innovation Lab.
In this conversation, we explore the world of circadian biology and how aligning our daily habits with our natural rhythms can transform our health. Kristen explains the far-reaching consequences of a disrupted circadian rhythm, from metabolic disorders and increased ageing to mental health challenges and lower immune function.
We discuss the critical importance of consistent sleep/wake times, even on weekends, and how this simple change can dramatically improve our psychological and physiological functioning. Kristen shares her personal experience of how aligning her circadian rhythms has boosted her productivity, focus, and overall health – she hasn’t been ill for over eight years.
Throughout our conversation, we explore strategies for harmonising our circadian rhythms within the context of modern life. We cover the importance of morning light exposure, the ideal meal timing, and how to manage factors like alcohol and caffeine consumption. Kristen also advises shift workers on maintaining healthy rhythms despite irregular schedules.
Circadian Rhythms: The Foundation of Health and Longevity
- Circadian rhythms are the physical, mental, and behavioural processes occurring over a 24-hour cycle.
- Circadian alignment (matching internal preferences with the light-dark cycle) is considered the foundation of health and longevity. When the circadian rhythm is not functioning optimally, any attempts to improve health through nutrition or exercise protocols will be less efficient.
- Misaligned or desynchronized circadian rhythms are associated with an increased risk of metabolic disorders and metabolic dysfunction. Furthermore, not a single mental health disorder exists that circadian rhythm disruption doesn't touch.
- The desynchronization causes cellular miscommunication, which is considered the basis of most disease and aging.
- Modernity, specifically 24/7 access to light and food, creates enormous stress on the system and leads to misalignment.
The Importance of Sleep-Wake Time Consistency
- Sleep-wake timing is highlighted as the most important behaviour to adopt for optimizing health and longevity.
- A stable sleep-wake time is the behaviour most protective of psychological health and mental health, even during periods of high stress (e.g., during the COVID-19 lockdown).
- In a highly healthy population (Collegiate athletes aged 18-23), just one hour of variability in sleep-wake time caused a degradation in Heart Rate Variability (HRV) and an increase in Resting Heart Rate (RHR). HRV is an incredible proxy for mental and physical health resilience.
- For every hour of variability between a person's weekday and weekend sleep-wake time (social jet lag), there was a 17% increase in non-suicidal self-injury in a study of college students.
- Consistently stable rhythms lead to more efficient sleep, meaning individuals may need to spend less time in bed because they have less light sleep and less awake time.
Practical Recommendations for Circadian Alignment
- The most important step in achieving a stable sleep-wake time is to wake up at the same time every day, which is a controllable behaviour.
- Upon waking, an individual should immediately get outside into the morning natural light (even if cloudy) for at least five to ten minutes to help set their circadian rhythm.
- The optimal time for receiving light input to set circadian rhythms is before 10 a.m. and as the sun is setting. There is a "Circadian dead zone" generally between 10 a.m. and 4 p.m..
- Most people are not as varied in their natural internal preferences (chronotypes) as they think; given natural light cycles (e.g., when camping), most people would fall asleep within a half-hour of each other.
- To protect sleep and recovery, people should aim to keep sleep debt under 45 minutes (the threshold beyond which collegiate athletes are predisposed to illness and injury).
- For stable sleep-wake time, the variability should ideally be kept below 30 minutes. Older individuals are generally more sensitive to variability.
- The bare minimum time people should spend outdoors daily for mental health benefits is 67 minutes.
The Timing of Food (Eating Window)
- The timing of meals is a critical factor that influences circadian rhythms.
- Only alcohol is reported to disrupt sleep and recovery markers (HRV, RHR, respiratory rate) more than a late meal.
- Consuming a late meal can compromise deeper stages of sleep (REM and slow-wave sleep), potentially resulting in 30 to 50 minutes more awake time and decreasing sleep efficiency by up to 17%.
- The recommendation for sleep consistency is to have the last calorie intake at least a two-hour buffer before intending to sleep.
- The bulk of calories should be consumed during the day (daylight hours) when the body is active and primed to metabolise food. We become more insulin resistant as the day progresses.
- While time-restricted eating focuses on consolidating the eating window during daylight hours (e.g., 8, 10, or 12 hours) and is not the same as intermittent fasting, eating during daylight hours can help achieve metabolic goals even if food quality is not optimal.
The Detrimental Effects of Alcohol and Caffeine
- No amount of alcohol appears to be good for resting physiology; it impacts resting heart rate, HRV, respiratory rate, and sleep markers. On average, if an individual consumes two or more drinks, it takes approximately five days to return to their physiological baseline (HRV, RHR, etc.). Alcohol consumption compresses the deeper stages of sleep, similar to a late meal. Alcohol's impact is not just physiological; it erodes the "headroom" available to deal with other life stresses, making individuals more vulnerable.
- Caffeine after 3 p.m. delays sleep onset for most people. A universal recommendation is that most folks should have their last sip of caffeine by noon.
- Viewing light regularly between 11 p.m. and 4 a.m. (often compounded by caffeine consumption) causes the dopamine system (motivation, reward) to work less effectively the following day.
- If experiencing short sleep, it's better to maintain the regular wake-up time, skip caffeine, and take a nap before 1 p.m. to help maintain circadian rhythm.
The Mind-Body Connection and Stress
- Physiology affects our psychology, and our psychology affects our physiology; they are a two-way system.
- When our internal values and external actions do not align, it creates internal dissonance or mismatch that manifests as unproductive and maladaptive behaviours.
- Chronic activation of stress systems (HPA axis, autonomic nervous system, and immune system) leads to illness and disease because the body is forced to work overtime. Creating a "buffer" in the system (e.g., stable sleep, good nutrition, social connections) is necessary to tolerate unavoidable life stressors.
- Mindset and Stress Perception: People who perceive their daily stress as challenging (a growth mindset) sleep better and are more recovered the next day, compared to those who perceive it as threatening, which can be paralyzing.
- An individual's ability to perceive stress as challenging is contingent on their foundation: having appropriate sleep, aligned circadian rhythms, positive relationships, a sense of control, and feeling they have the skills and resources to take on tasks.
Addressing Shift Work and High-Risk Lifestyles
- Shift workers, who perform critical jobs while living with chronic circadian rhythm disruption, require specific strategies to minimise stress on their system.
- Consume the largest, most nutrient-dense meal when still relatively primed (e.g., 3 p.m./4 p.m. before the shift).
- Minimise light exposure in the lead-up to bed (e.g., wear sunglasses and a hat) to prevent the system from waking up.
- Go to bed as soon as possible after the shift ends (e.g., around 7 a.m.) to maximise consolidated sleep hours; delaying sleep leads to shorter and more fragmented rest.
- Use creatine supplementation, as it is protective against symptoms of sleep deprivation and highly relevant for this often deficient population.
- Maintain hydration, as dehydration is a third major factor that impacts sleep and recovery.
- Stop caffeine intake at least eight hours before intending to sleep (e.g., midnight for an 8 a.m. sleep).
- Reverting to Day Shift: Individuals should have a big breakfast, avoid caffeine, get bright light exposure and exercise in the morning, and take a 90-minute to 3-hour nap around 11 a.m./12 p.m. to relieve sleep pressure without compromising night sleep.