#65 Dr. Satchin Panda on Circadian Insights into Exercise Timing, Melatonin Biology, and Peak Cognition

Posted on June 15th 2021 (over 3 years)

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Dr. Satchidananda ("Satchin") Panda is a professor in the Regulatory Biology Laboratory at the Salk Institute for Biological Studies. His work focuses on chronobiology, the study of the day-night cycles that drive the multifaceted activities of the human body, using genetic, genomic, and biochemical approaches. He is an expert on circadian rhythms and a pioneer in the field of time-restricted eating. A priority for Dr. Panda when designing his studies is to identify strategies that positively impact public health.

Circadian rhythms, the body’s 24-hour cycles of biological, hormonal, and behavioral patterns, modulate a wide array of physiological processes, including the body’s production of hormones that regulate sleep, hunger, and metabolism, ultimately influencing body weight, performance, and susceptibility to disease. Circadian rhythmicity may have profound implications for human healthspan.

When and how much we sleep, eat, or exercise (and these activities' effects on our health) are intrinsically linked to our circadian rhythms.

In this episode, Dr. Panda and I discuss...

  • How circadian rhythms influence human health.
  • How seeking bright light in the morning and avoiding it in the evening can help us sleep better.
  • How the ability of supplemental melatonin to counteract evening bright light exposure varies.
  • How understanding the relationship between melatonin and insulin secretion might help us decide when to eat.
  • How shift work, jet lag, and modern lifestyles contribute to altered circadian rhythms and metabolic dysfunction.
  • How naps might aid with afternoon sleepiness and sleep loss.
  • How we can tailor our indoor lighting environment to promote healthy circadian rhythms.
  • How time-restricted eating (eating within a narrow time range) can be beneficial.
  • How Dr. Panda's ongoing study uses a smartphone app to track when people eat.
  • How most people are unaware of their eating patterns.
  • How Dr. Panda incorporates his research findings into his own life.
  • How our circadian rhythms dictate when we should exercise – and how caffeine provides a workaround.

Chronobiology – understanding the body's highly orchestrated concert of functions.

"Every single organ, every single cell, has its own daily timed circadian rhythms."- Satchin Panda, Ph.D. Click To Tweet

The human body is complex. A vast array of hormones, chemicals, and processes operate day and night in concert to regulate diverse physiological and metabolic processes. To assure these tasks are performed appropriately, the body adheres to timetables, known as circadian rhythms. These rhythms provide the cues that regulate every aspect of our lives, from when we eat and sleep to when we should take certain medications or get vaccinated. Even neurotransmitters have circadian rhythms, elevating our moods at certain times of the day – and perhaps darkening them at others.

A key driver of circadian rhythms is melatonin. Often called the sleepiness hormone, melatonin is a protein produced primarily in the pineal gland of the brain. Its levels oscillate daily, peaking one hour into sleep and ebbing two hours after waking.

Non-visual photoreceptors in the eyes regulate circadian clocks

"This blue light sensor in our retina connects to our brain to reset our clock or to tell when melatonin should rise or fall."- Satchin Panda, Ph.D. Click To Tweet

Light is the primary signal that guides the schedule of the circadian cycles. Dr. Panda and his colleagues discovered that specialized cells in the eye, called intrinsically photosensitive retinal ganglion cells, entrain the circadian clock to light, ultimately regulating melatonin release. These photoreceptive cells do not participate in vision; rather, they contain melanopsin, a light-sensitive protein. Melanopsin-containing cells respond to light (or its absence) and direct the master circadian clock to suppress (or release) melatonin.

Blue light – seek it in the morning, avoid it in the evening

Blue light, a wavelength of light emitted from both natural and artificial sources, suppresses melatonin, resetting the circadian clock and switching on the activity of hundreds of genes – the signal for rising. Exposure to blue light is associated with improved attention span, reaction time, and mood.

In the past, humans' primary exposure to blue light was from the sun, but in modern times, electronic devices – TVs, computer screens, and cell phones – expose us to increasing amounts of blue light, often during times of the day or night that are out of sync with our bodies' natural rhythms. Dimming lights and curtailing our use of these devices in the evening allows melatonin to rise naturally, so we can sleep.

A surprising connection between melatonin and blood sugar control

"It might be a good idea to wait for an hour or two after waking for melatonin levels to come back to daytime levels before eating. At night it's good to not eat or drink anything that has carbohydrates or glucose two hours before bed." - Satchin Panda, Ph.D. Click To Tweet

Several converging branches of evidence suggest that melatonin inhibits insulin secretion, influencing blood glucose levels. Clinicians have regularly observed that their patients' insulin sensitivity worsens in the evening hours. Genetic studies have revealed that carriers of a variant of the melatonin receptor gene (MTNR1B) are more likely to have obesity or diabetes. And rodent studies demonstrate that insulin-producing beta cells in the pancreas decrease the amount of insulin they release in response to raised melatonin levels.

This compendium of evidence indicates that melatonin puts the pancreas to sleep, much like it puts the brain to sleep. As a result, eating too close to bedtime or immediately upon waking – before nightly melatonin levels have returned to daytime levels – may hamper the body's ability to process glucose.

Food timing is a critical variable in health

"If you ate or drank something that has calories maybe two to three hours after your dinner time just for one day in a week, that can have an impact on your circadian rhythm for two to three days."- Satchin Panda, Ph.D. Click To Tweet

Having an extended window of eating carries risks, too. The body needs time apart from digesting food for repair and rejuvenation. Dr. Panda and his colleagues observed that when mice ate within a brief, defined time window, they had fewer metabolic diseases. This practice, known as time-restricted feeding, helped sustain healthy circadian rhythms in the mice – and showed promise as a strategy to improve health in humans.

Altered perception about the eating window

But most people aren't fully aware of how much time they spend eating. When asked about their eating habits, people typically report that they eat within a brief time window. But the reality is quite different. An app created by Dr. Panda and his colleagues revealed that half of the app users had an eating window of 15 hours or longer, and only 10 percent of the users had an eating window of 12 hours or less. In contrast, most people self-report having an eating window of 13 hours per day.

Circadian rhythms dictate when we're at our best – physically and mentally

"There are a lot of studies that are coming out saying that late afternoon or evening may be the best time for exercise."- Satchin Panda, Ph.D. Click To Tweet

The mere fact that the body has these rigid timetables and schedules suggests that there are times during the day when human performance is optimized. Evidence bears this out in terms of cognitive performance and exercise.

Cognitive performance peaks early, with problem-solving ability typically occurring during the first half of the day. Conversely, exercise may be most beneficial when performed later in the day. Late afternoon or evening exercise improves blood glucose levels in people with type 2 diabetes. Similarly, an afternoon workout improves exercise-induced fat oxidation. But for those who prefer that morning workout, caffeine boosts fat oxidation during morning exercise.

A role for caffeine in circadian rhythms

Staying up late at night or eating food when the body is less capable of metabolizing it ignores the body's natural rhythms. The body and brain respond accordingly, with declined performance. To counteract these declines, people often turn to stimulants such as caffeine. Unfortunately, caffeine doesn't make us think clearly, it just makes us more alert.

Even though the field of chronobiology is young, scientists have noted that disrupted circadian rhythms pose serious health concerns rather than mere annoyances. These exciting findings are readily translatable, allowing people to adopt habits and design their living and workspaces to optimize circadian rhythms – working with our circadian rhythms, rather than against them – can have profound impacts on personal and public health.

Relevant publications

Learn more about Dr. Satchin Panda

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