Melatonin

Most modern people accept that the “correct” way to sleep is to go to bed at night and stay asleep until morning. In fact, waking at night and being unable to go back to sleep is often considered a sleep disorder. However, there is evidence that humans did not always consider a full night of uninterrupted sleep ideal. Choosing to engage in “two sleeps” may be a common pattern in human history—and a healthy pattern as well.

Bimodal Sleep in Human History

Bimodal, or segmented, sleep appears to have been the way that many of our ancestors slept. Ancient physicians, as well as authors such as Charles Dickens and Chaucer, refer to a first and second sleep in their writings, with the time between the two sleeps spent engaged in quiet activities. Historians believe that this habit disappeared some time around the turn of the twentieth century when electrical light became common.

Just 200 years ago, people routinely woke at night to socialize, pray, read, have sex and otherwise enjoy some quiet time. Most people stayed in bed during this time, although some got up for short periods. The practice of two sleeps appears to have been especially common among the working classes, who were too worn out to be productive immediately after arriving home from a day of manual labor. Doctors even recommended the period between the first and second sleep as the best time to conceive a child.

The Problem of Middle-of-the-Night Insomnia

The very sleep pattern that our ancestors viewed as normal is now often considered a sleep disorder. Sleep maintenance, or middle-of-the-night insomnia, is the most common type of insomnia in the United States. While this disorder can be caused by GERD, anxiety and other health disorders, many people who experience it appear to have no physical cause. Doctors recommend that people who wake at night and cannot get back to sleep do some type of sedentary activity in low light and go back to sleep when they are able, which is strikingly similar to how our ancestors once passed midnight hours.

Middle-of-the-night insomnia may be common because it is a normal human sleep pattern. Could it be that some people who believe they have a sleep disorder may in fact just need to rearrange their evening and night time schedules to allow two sleeps?

Are Two Sleeps Really Better Than One?

Researchers believe that ancient humans tended to sleep around three-and-a-half hours in each sleep cycle, with around two hours between the first and second sleep. Melatonin levels remain high throughout both sleeps and the quiet wakeful phase in between, while the sleepiness preceding the second sleep is caused by a surge in the sex hormone progesterone. Choline levels also differ in people who follow the practice of segmented sleeps. This means that the second sleep has more cholinergic REM phases, which causes more restful slumber and more lucid dreams.

For many people, it could be that middle-of-the-night insomnia is not so much a sleep disorder as a sign that they need two sleeps rather than one. That nighttime period of wakefulness may be the most creative time, while the second sleep appears to be more restful than a normal continuous seven-hour sleep.

Why Did We Start Sleeping in One Block?

If sleeping in two blocks is healthy, why did people stop? There are a few suggested reasons. First, electric light made it possible for people to stay up later at night, making it difficult to get in two full blocks of sleep plus a rest period. Second, the world began to focus more on efficiency. Suddenly, laying in bed and being relatively unproductive for several hours every night was viewed as a waste of time.

While most people have adapted to the practice of sleeping in one seven to eight-hour block, some still struggle. Sleep maintenance insomnia may merely be a return to old ways, which explains why it is so hard to treat. If you have trouble with waking in the middle of the night, it may be time to see if segmented sleep, or engaging in two sleeps, works better for your body.

If you’ve been keeping up with recent research, you’re probably aware of the negative effects of blue light from electronic devices on sleep. More and more we are being warned to put down the smartphone and power down the laptop at night. The link between low melatonin levels and blue light is well established. However, blue light may be affecting us in more ways than we previously realized.

Light, Melatonin and Sleep

Throughout human history, people have gone to bed shortly after dark. Our bodies are biochemically primed for this behavior. When our retinas stop sensing light, they send a message to the suprachiasmatic nucleus (SCN) of the hypothalamus. This part of the brain functions as the timer for our internal clocks, setting off a cascade of events that prepare us for sleep. One of the main ways this happens is through the release of melatonin in the pineal gland. Conversely, in the early morning hours when light first appears, melatonin production is shut down. At this time, our bodies switch to making cortisol and other hormones that increase alertness.

Realistically, a day in modern life does not end at sundown. We are exposed to artificial lighting from a variety of sources including light bulbs, televisions, computers and smartphones. Although even dim artificial light can affect melatonin production, it appears that the effects of blue light, such as that emitted from devices like tablets and smartphones, may be even greater.

More Than Melatonin: The Problem With Blue Light

Blue light is constantly present in our world. How many people go to bed with an e-reader, tablet, or smartphone in hand? This can have an immense impact on how long it takes us to fall asleep, as well as the quality of our sleep. Human eyes have special wavelength-sensitive photoreceptors that sense blue light, which appear to shut down melatonin production more effectively than other kinds of receptors in the eye.

Mice also have a circadian rhythm, although it is the opposite of ours. Mice are nocturnal and sleep mainly throughout the day, which means they are primed to produce melatonin and fall asleep in the presence of light. Although they have a very different reaction to light than humans, they have the same receptors for blue light in their retinas. When exposed to light, mice in a recent experiment became sleepy as expected. However, when exposed solely to blue light, these mice became more active and took much longer to fall asleep. This did not occur in mice who were bred to lack the blue-light photoreceptors.

Interestingly, blue light appeared to delay their sleep as much as it does in humans, having more of an effect than green and violet light. Scientists behind these studies believe this is because blue light may also increase levels of stress hormones like cortisol. These hormones are cues for wakefulness, explaining the wakening effects of blue light on both diurnal and nocturnal animals.

Blue Light: A Possible Cause of Circadian Rhythm Disruption

While blue light is present in sunlight, it is present in far lower amounts than that seen in electronic devices. Sunlight contains the full spectrum of light, which is why it can be refracted into a rainbow. On the other hand, most devices contain almost exclusively blue wavelengths of light. Given that blue light reduces melatonin production and may even increase cortisol levels, this has immense implications for human health.

Sleep disorders are on the rise in the United States; increasing blue light levels in our environment that inhibit melatonin production and increase stress hormone levels may be part of the cause. However, many people are tied to their devices. We use smartphones and tablets to perform work, to communicate with friends, even to read a book. Can modern people find a balance that allows them to get the sleep they need? This is the question for chronobiology researchers and other scientists who study circadian rhythm.

Benjamin Franklin once observed, “Early to bed and early to rise makes a man healthy, wealthy and wise.” However, in reality, it may not be so simple. While some people are up with dawn and yawning by dusk, others come alive at night, yet struggle to function in the mornings. New research has found that whether you are a “morning lark” or a “night owl” is determined by your genes. How you manage your chronotype and your lifestyle can have far-reaching effects on your health.

What Are Chronotypes?

Your chronotype is generally set by your sleep midpoint. For instance, a person who naturally goes to sleep at midnight and wakes up at 8 a.m. will have a midpoint of 4 a.m., making them a natural night owl. People who go to sleep early and wake early naturally are morning larks.

Our internal clocks shift slightly during our lives. Most small children are naturally morning larks, as many bleary-eyed parents have observed. However, this schedule has shifted by adolescence. Adolescents and young adults naturally lean toward a later bedtime and sleeping in well past dawn. On the other hand, the elderly move back to an early bedtime. However, there is variation even within this general pattern. For example, some toddlers are consistently up at 4 a.m. while others “sleep in” until 7 a.m.

Society has classically viewed night owls as lazy. These people struggle to get up and off to work or school early in the morning and are often not on the job during their most productive hours of the day. This may make them appear lazier, when in fact they are suffering from a phenomenon known as social jet lag, or a mismatch between outside obligations and internal rhythms. New research suggests that the difference between night owls and morning larks is not based on motivation and morality, but rather on genetics.

What Determines Your Chronotype?

Scientists have discovered that different chronotypes have measurably different levels of proteins associated with the circadian rhythm and even different variants of genes associated with the sleep-wake cycle. In a recent chronobiology study, a group of people with varying chronotypes were tested for salivary levels of melatonin and expression of the circadian rhythm genes Per1, Per2, and Rev-erbα. Researchers found that night owls had later expression of melatonin than morning larks, which means these people were biochemically primed to sleep and wake at different times. Considering that a person’s amount and quality of sleep can have immense effects on both lifestyle and health, this can affect a natural night owl’s life in a variety of ways.

Marching to the Beat of Your Internal Clock

Ideally, people would be able to work and go to school at the times when they are primed to be productive. They would also be able to sleep when they are biologically intended to do so. However, this is not the case for many modern people. Many night owls are crawling out of bed in the morning far before their sleep cycles have completed; many morning larks are forced to be awake past their natural bedtime for various obligations. The result is not just a society of sleepy people, but one of unhealthy people. Living out-of-sync with your chronotype can have a variety of health consequences.

The Health Risks of Ignoring Your Circadian Rhythm

What, exactly, happens when people are forced to live out of sync with their chronotype? As researcher Frank Scheer noted in the Proceedings of the National Academy of Sciences, this can cause “a decrease in leptin, increase in glucose and insulin, increase in mean arterial blood pressure and reduced sleep efficiency.” This leads to an increased risk of metabolic syndrome, cardiovascular disease and a variety of health disorders.

However, night owls do not necessarily need to suffer from diseases associated with circadian rhythm disorders. When allowed to change their schedule to match their natural sleep-wake cycles, people suffer no additional health risks. Being a night owl is not in itself unhealthy unless you try to act like a morning lark.

Our work and other activities were once limited to the hours when there is natural light. However, modern technology and artificial lighting allow us to be productive at any time. Allowing night owls and morning larks to work and learn when they are primed to be so may not just create a more productive workforce, but a healthier one as well.