WHAT'S HAPPENING: Circadian rhythms and sleep

Check out this latest curation of news stories appearing since June 1 which focus on a critical part of the sleeping process: Circadian Rhythms.  Topics discussed in this latest curation include:

• Circadian rhythm basics, including recent sleep research, light simulation, social interactions influenced by the circadian system, the color of light and its impact on sleep, the rhythms of the blind, the sleep homeostat, the clocks of the brain and the gut, genetics and the circadian system
• The time cues ("zeitgebers") that inform our rhythms, such as meals, exercising, managing time zone changes during the Olympics, and sleeping in space
• Chronotypes (are you a morning lark or a night owl?)
• Sleep problems like jet lag, shift work disorder, pain "rhythms," circadian rhythm disruption, intermittent short sleep, breaks in daily melatonin rhythmicity, and the down side of naps
• Light pollution as a major influence on sleep health

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ABCs of SLEEP || E is for Entrainment

Entrainment is the word scientists use to explain how we all, as human beings, "set our clocks." Our human body clocks, to be specific. Our bodies have multiple "clocks" in specific organs as well as inside each and every blood cell, and like clockwork they help us to manage our daily rhythms, which inform the behaviors that make us functioning human beings.

Think about hunger, sleep, sex, digestion. These are all physiological processes that require some precise timing on the part of our personal clocks. This is what our circadian rhythms are all about. When our rhythms fall out of synchronicity, that is when we can experience disease, general malaise or other kinds of biological confusion. We really can't live healthy lives without adhering to circadian rhythms.

The most obvious way that we entrain ourselves to life's rhythms is through our perception of light. Light is what marks the day/night cycles; the sun rises, the sun sets. Sunlight, and its absence, also helps the body to detect seasonal shifts. These are primal communications we share with the earth. All living things require the light-dark cycles, as established by the rotations of our planet, to manage these critical life rhythms. 

Light is perceived by the eyes, of course, but also through the skin via melanopsin. Signals collected by these organs are sent to the body's main pacemaker, the suprachiasmatic nucleus (SCN), which issues orders to all others parts of the body to function according to a preset pattern of rhythms that, by and large, most human beings are commonly entrained to using light.

For the vast majority of human beings, light is the key influence over when we sleep and when we wake up. For those with circadian rhythm disorders like Non-24 Sleep -Wake Disorder (also known as free-running disorder) or shift work disorder or even a temporary case of jet lag, light doesn't deliver the same influence over sleep-wake cycles. 

The person who suffers from these kinds of disorders struggles to maintain a normal life on an abnormal schedule. They have fallen out of entrainment and need to find a way to "reset" or else they are forced to adjust their schedule in ways that are not typical, even unorthodox, in order to simply get by. 

Imagine the person who can only feel awake and alert in the later afternoon; maybe they have a job working at the toll both during the morning commute. Or imagine the nurse who can only work night shifts but who has children to watch during the day at home. Or the musician who cannot stay awake long enough to attend the gigs he is scheduled to perform at nightclubs. 

Having pattern disruptions in one's rhythms can absolutely devastate the efforts of many to live normally (in this case, meaning "by society's schedule"), and that includes having the ability to earn a living, care for family or function at their maximum potential while on the job. Circadian rhythm disorders also seriously disrupt relationships and social lives.

Non-visual cues

Believe it or not, there are other cues besides light--in science, they call them zeitgebers, which translates as time markers, external or environmental cues that synchronize our biological rhythms--which have a powerful impact on our lives, including our time while sleeping. These are also ways we are entrained to healthy--or unhealthy--rhythms. 

Eating and digesting do not require light or even sight to take place. They require that the gastrointestinal system follow specific cues that dictate that you eat and digest while you are awake. While you sleep, the digestive system goes into sleep mode as well. This is why, generally speaking, most people do not get up in the middle of the night to have a bowel movement. The digestive system does not expect food to enter the alimentary canal at this time. Instead, the act of moving food through the system slows dramatically.

Large meals eaten right before bed, however, can create problems with sleep disruption; the digestive system is suddenly working overtime when it had fully expected to be in bed like the rest of you. Poor sleep can result, as can reflux disease and other health problems related to metabolism. There are lots of studies to suggest that eating out of synch with one's normal body rhythms (meaning, late at night) can lead to imbalanced secretions of certain hormones like melatonin, orexin, leptin and ghrelin, which can impact metabolism in negative ways. 

Finally, there is a circadian shift in metabolism that occurs in the morning as part of your biological rhythms. This is normal; it prompts hunger and stimulates the body to recommence digestion. Now you know why we almost always need to use the restroom first thing in the morning: wakefulness stimulates digestion and the elimination of wastes that have been in your "holding tanks" (meaning, the bladder and the bowel) overnight.

This illustration from the University of Zurich shows how the brain and digestive organs carry their own "pacemakers." The main pacemaker in the body is the suprachiasmatic nucleus (SCN), which is located
deep inside the brain. Its companion pacemakers exist in the digestive system and are driven
by information related to internal cues relayed to them via messages sent by the SCN. 

Activity levels are other non-light time markers that can inform sleep-wake cycles and metabolism. If you exercise too late at night, this could mess with your ability to fall asleep. Physical activity (it could be running a mile or doing laundry) amps up adrenaline and other hormones which encourage wakefulness. 

Similarly, body temperature, which is influenced by how physically active you are, impacts your ability to entrain to patterns that allow for consistent sleep-wake patterns. If you do not get enough physical activity during the day, you may find it hard to fall asleep, as well--with no normal rise and fall in daytime body temperature, the body may not be able to read your activity markers clearly enough to signal sleep to occur. 

Also, the act of sleeping itself is marked by specific patterns of body temperature shifting that prepare the brain and body systems for specific kinds of sleep. If your body temperature is out of whack as you are heading off to bed, you might be missing out on sleep stages that are critical to your body and brain to function at maximum potential.

Temperature-related breaks in entrainment are experienced by people with major stress disorders like PTSD or severe depression: they may generate higher body temperatures at night while in stress response even as they are hoping to fall asleep. Women, because of their monthly cycles, can also experience temporary periods of sleep disruption due to normal alterations in body temperature caused by menstruation or other major changes in hormone balance like pregnancy or menopause.

SHED SOME LIGHT: Sleep Hygiene Tip of the Week: Managing jet lag while traveling over the holiday

"Over the river and through the woods to Grandmother's house we go..."

NOT... Grandmother lives in Miami and you live in Denver. Your siblings and their families live in Fargo; Trenton, New Jersey; and Memphis.

"Nightly Rotation Above San Jose International
Airport" (2005) by Wing-Chi Poon. CC:ASA-2.5 Generic.

These days, airlines have replaced the old-timey sleighs that carted families from one town to the next for special occasions like Thanksgiving.

If you are someone who lives far away from family and must rely on flights to be reunited, then you likely admire those who only have to make the quick drive across town or even the few hours on the highway.

Traveling in the winter, especially, takes extra time and extra energy to sort through all the delays that might arise due to weather and overbookings.

What makes things worse is that every time you hop a time zone (forward or backward), you confuse your body clocks. The more time zones you cross during a continental flight, the more confused your body clocks will be.

Your main clock, located in the suprachiasmatic nucleus in the brain, will find changes in light exposure (too little when the brain expects there to be light, or too much light when the brain expects there to be little) overwhelming.

It's not a force of habit that leads to the symptoms of exhaustion that we have come to term jet lag, but actually a reshuffling of chemical balances in the brain, which has been confused by these external queues and suddenly cannot reset itself accordingly. It is essentially out of rhythm with the rest of the body.

Circadian rhythms are informed by the light and dark cycles of the earth. They also take their cues from our activity levels (the body naturally is more energetic in the morning and less energetic in the evening, for example) and our eating habits. Our digestive system does not expect to be processing a main meal several hours before or after it normally does this task; meals eaten much later than normal are especially troublesome because that is when key organs in the body, which operate on their own clocks--which are synchronized to the main clock--are trying to rest.

What this all amounts to is a sense of disorientation, however temporary, plus feeling less than 100 percent. Fatigue, gasiness and bloating, dehydration and insomnia can all be side effects from hopping time zones.

Technically speaking, jet lag has been taken off the list of circadian rhythm disorders because of its temporary nature... everyone eventually recovers from these shifts in the body's rhythms when they return home. That doesn't make it easier to manage during stressful times like the holidays, however.

There are ways to help yourself so that these feelings of travel-related malaise aren't quite so extreme.

• Drinking water before, during and after the plane ride (and not coffee, alcohol or soda) will help keep your body in balance through changes in temperature, climate and cabin pressurization. In fact, most of your discomfort from jet lag will come because of dehydration.
• How many hours are you traveling east? Three? Then start shifting your schedule by going to bed a half hour earlier on Saturday, then an hour earlier on Sunday, then an hour and a half earlier on Monday, two hours earlier on Tuesday, two and a half hours earlier on Wednesday. Reverse this plan if you are traveling west across three time zones. It may seem extreme but if you really need all your energy for the holidays themselves, you will thank yourself later for planning ahead so you won't need to endure the fatigue/insomnia showdown that can come with jet lag later.
• On your travel days, curb your eating. Don't eat a big meal before getting on the plane. Try not to eat a full meal on the plane, as well (a snack would be okay if you really are hungry), then wait until you are off the plane. Once you are at your destination, eat only during the local meal time. This will make it easier to adjust for the holidays when you really want to enjoy those family meals together.
• Use earplugs, eye masks, blankets and neck pillows to sleep comfortably on the plane, should you be traveling during a time you would normally sleep. However, try not to oversleep on the plane; only sleep when your body needs it or you might rob yourself of your sleep drive prematurely.

Insomnia Central || The "walrus"* in space

You'd think it's plenty quiet and dark in space... so how does it happen that astronauts struggle with insomnia?

All living things (including humans, plants and animals) have photoreceptors which recognize the difference between light and dark cycles. These light cues (known in the sleep world as zeitgebers), help us to stay awake during the day and to fall asleep at night. Melatonin production in the brain increases as the sky darkens in the afternoon, then drops off dramatically with the first peek of daylight in the morning.

Astronauts, however, have a different relationship with sunrises and sunsets while working on the International Space Station, where the sun rises and sets every 90 minutes. This rapidly shifting rhythm of light to dark can seriously impose itself on the human circadian system, which is entrained to 24-hour days. Over time, this can lead to hormonal confusion in the brain and, ultimately, insomnia for these space walkers.

Insomniac astronauts are not a good idea. What this could mean is that, during their waking hours, these sleep-deprived astronauts may share a common risk-taking behavior with long-haul truckers, bus drivers and airline pilots: drowsy driving. Lack of quality sleep can result in poor judgment, inability to achieve an appropriate level of alertness in emergency situations, even the opportunity to "sleep drive" (like sleepwalking, but while driving).

Most astronauts end up taking Ambien (aka zolpidem as a generic) to regulate their sleep cycles and comply with their daily requirement of 8.5 hours of sleep, but Ambien can leave them with a foggy morning-after hangover that can impair their performance nearly as much as sleep deprivation. It can also be to blame for some unusual behaviors that can occur while asleep which are typically hallucinatory in nature and may resemble sleep walking.

So which is better... sleep deprived astronauts or hallucinating ones?

Dr Charles Czeisler, a Harvard Medical School sleep expert who co-authored a recent article for Lancet about the problem of sleep for astronauts, said: "Future exploration spaceflight missions to the moon, Mars, or beyond will require more effective countermeasures to optimize human performance by promoting sleep during spaceflight... These may include modifications to schedules, strategically timed exposure to specific wavelengths of light, and behavioral strategies to ensure adequate sleep, which is essential for maintaining health, performance and safety."

So really, the answer is neither. Humans need sleep, even and, perhaps, especially, those who don't have their feet solidly planted on the terra firma.

Read more:

• Sleeping pills in space: Astronauts are regular users || USA Today
• What it's like for astronauts to sleep in space || The Atlantic
• Sleep, the final frontier: Astronauts suffer serious insomnia while in space - and it could be putting their lives in danger || The Daily Mail (UK)

*Ambien is popularly referred to as "the walrus" after a comic strip artist began to write about Ambien experiences in which a "walrus" told him things while he was under its influence.