Circadian Rhythm

It is a classic “chicken-or-egg” argument: What came first in the evolutionary development of all species of animals — sleep or the brain? When looking at the origin of sleep, the question often leads to speculation about the evolution of this imperative biological act. New research continues to shed light on this fascinating debate.

Sleep is Universal

One thing that is clearly understood is that sleep is universal in the animal kingdom. Scientists have had a challenging time finding animals that do not need sleep. While some species spend nearly the entirety of their lives in slumber, other animals can get by with just an hour of sleep per 24-hour cycle. However, the universal truth is that sleep and the need to rest comes in one way or another.

Role of Sleep in Evolution

Research has demonstrated that sleep may have evolved as a means for animals to conserve and restore energy stores. Even simple invertebrates exhibit the need to rest similar to the sleep patterns of the most complex organisms.

For example, fruit flies show well-defined circadian rhythms that mimic the rest patterns of humans. These simple flies rest for approximately 10 hours per day. If they are not able to get that length of rest, they will make it up at a later time, pointing to the fact that the rest is an essential biological function.

The need for fruit flies to make up the sleep is similar to the human need to catch up on those zzz’s after a restless night. Scientists have also discovered that like more complex vertebrates, invertebrates also exhibit neural activity that is similar to what happens in the brains of vertebrates when they are sleeping.

In light of these similarities, scientists have been able to deduce that sleep is an evolutionary process that emerged over half a billion years ago. Because animals have evolved over the centuries, it appears as if these forms of sleep have also evolved along with the natural evolution of species.

Research Confirms Origin of Sleep

While scientists have hypothesized for years that the need to sleep is universal throughout all types of animals, there is now evidence that points to the idea that animals acquired the need to sleep before even acquiring a brain.

In a recent study published last fall in the journal Science Advances, a team of researchers detailed how they were able to better understand the origin of the need for sleep in animals by looking at tiny hydras. This minuscule water-dwelling species of animal is so simple that it does not even have a brain. However, the researchers were able to prove that this animal still shows signs of going in and out of a sleep-like state despite the fact that it does not have a central nervous system.

Hydras measure just a few centimeters long. While their bodies are home to a network of nerves, they do not have the central nervous system associated with a brain. Sleep in most other types of animals is usually measured in brain waves. However, this is not possible when looking at small and brainless creatures such as hydras. Because of this limitation, the scientists leaned on a video system to track the movements of the hydras. This helped them to determine if the animal was in a sleep-like or waking state.

While most animals exhibit a 24-hour circadian rhythm, the scientists were able to discern that the hydras had a four-hour cycle that moved in and out of active and sleep-like states. Additionally, the researchers learned that there were similar patterns of sleep regulation on both the molecular and genetic levels, despite the fact that hydras have no brain.

For example, when exposed to melatonin and the inhibitory neurotransmitter GABA, the hydras experienced a moderate increase in sleep frequency and duration of restfulness. Conversely, exposing the hydras to the arousing stimulant dopamine worked to promote more sleep cycles in the hydras.

Lastly, scientists were able to successfully disrupt the sleep cycles of the hydras using vibrations or by changing the temperature of the water. When the cycles were thrown into disarray, the hydras slept longer afterward to catch up on the rest that they missed because of the disruption.

This new research complements existing knowledge that showed that jellyfish also exhibit periods of rest in the absence of a formal central nervous system and brain. The takeaway from this research is that animals likely acquired all of the sleep-related mechanisms before the central nervous system developed.

Why This Knowledge is Important

So why is understanding the origin of sleep so important? As scientists learn more about the evolution of sleep, it also helps them to learn more about the function of this critical biological action. This knowledge helps medical researchers to understand more about sleep disorders so that they can treat them more effectively.

With the prevalence of sleep disorders throughout the population, the more that it is understood about this vital body function, the better that scientists will be able to provide treatments for those in need.

As the vast body of evidence linking sleep quality and circadian rhythms to physical health, cognitive performance and mental well-being continues to grow, many scientists and health care professionals are casting an inquiring eye on Daylight Savings time. There’s far more than just an hour of sleep at play with this time shift. Of course, in this chronically sleep deprived era, that hour shouldn’t be considered an inconsequential springtime loss. However, it is also the artificial extension of daylight hours into the evening that may make Daylight Saving Time bad for your health.

Sleep Quality Essential to Health

Daylight Saving Time is disruptive to sleep. Sleep quality, meaning a sufficient amount and quality that allows you to successfully move through all of the sleep stages, impacts physical and cognitive health in a number of ways. Disruption of sleep, including not sleeping enough, can have far-reaching negative short-term and long-term effects on health and well-being. Short-term effects include decreased cognitive performance, particularly in the realms of memory and learning, an increased risk of mood and emotional disorders and a higher risk of workplace injuries and traffic accidents. Long-term impacts include an increased risk of some cancers, obesity, type two diabetes, clinical depression and cardiovascular disease.

Distinct Impact Patterns Suggest Daylight Saving Time Bad for Many

Depending on the person, it can typically take between three days and a week to adjust to the Daylight Saving Time shift. However, not everybody is typical. It can take some people significantly longer to adapt, with some never fully adapting to the time shift. For those with a chronic health condition that can be a hard, even dangerous adjustment period. Cardiac incident patterns offer a clear example of that.

Numerous studies point to a distinct pattern of adverse cardiac events associated with Daylight Saving Time. The number of heart attacks and strokes typically increases in the days immediately following the time shift. Interestingly, a 2014 study published in Open Heart found that the number of heart attacks on the Monday after Daylight Saving Time began increased by 25 percent, then on the Tuesday after the return of Standard Time in the fall, decreased by 21 percent.

The time shifts into and out of Daylight Saving Time are associated with higher numbers of strokes during the few days after the change, as well as other conditions that impact stroke risk. These include high blood pressure and, in the autumn, with the return to Standard Time and an abrupt loss of evening light, an increased risk of depression.

It’s Much Bigger Than an Hour

That abrupt loss of evening light is a much bigger deal that it may seem at first glance. The same could be said about the hour shift in time, as both are connected by their importance to the circadian rhythm. The circadian rhythm is a vital link in the functioning of the entire body, including the brain. Electrical impulses and chemical interactions and reactions are at the root of every single bodily process, ranging from the production of hormones to essential metabolic processes to the ability of the brain to communicate with the body. The circadian rhythm helps to regulate the timing of these processes via an overarching system of body clocks that influence physical actions and processes down to the cellular level. Balanced, smooth functioning helps to produce good health and protect the body from disease.

Over countless generations, from our very origins as a species, we have evolved in conjunction with the pattern of day and night. That approximately 24-hour cycle of light and dark is a part of us and a part of how our bodies and minds work on a deep, mechanical level. Daylight Saving Time disrupts that significantly and not just by an hour lost or gained in sleeping time.

Due to that ancient evolutionary pattern, light is one of the primary environmental cues for our circadian rhythm. We have light sensitive cells in our retinas and brains that help to set our body clocks, thereby influencing the timing of bodily functions and brain tasks. The artificial shifting of sunrise and sunset times deprives us of the natural lighting patterns we need for a smooth adjustment to seasonal changes, allowing for the disruption of the highly complex systems that support health and well-being on the most basic levels. Science is increasingly demonstrating that such disruption is strongly linked to a wide range of diseases and chronic health conditions.

Prepare to Mitigate Impact

While scientists point to Standard Time as being best aligned to our what our circadian rhythms require for optimal functioning, many of us still have to deal with Daylight Saving Time. Preparing for the time change can help mitigate the impact. Start shifting your waking and sleeping times gradually a week or two in advance and practice good sleep hygiene. Add a little physical activity in morning sunlight to your daily routine to support your circadian rhythm. Lighten your evening meals and reduce your caffeine during your time transition phase. If the adjustment tends to be more difficult for you, consider a melatonin supplement to ease the transition.