THE BODY CLOCK

Have you ever noticed that you tend to feel energized and drowsy around the same times every day ? This is circadian rhythm. So what is it, exactly? Your circadian rhythm is basically a 24-hour internal clock that is running in the background of your brain and cycles between sleepiness and alertness at regular intervals. It's also known as your sleep/wake cycle.

For most adults, the biggest dip in energy happens in the middle of the night (somewhere between 2:00am and 4:00am, when they're usually fast asleep) and just after lunchtime (around 1:00pm to 3:00pm, when they tend to crave a post-lunch nap). Those times can be different if you’re naturally a night owl or a morning person. You also won’t feel the dips and rises of your circadian rhythm as strongly if you’re all caught up on sleep. It’s when you’re sleep-deprived that you’ll notice bigger swings of sleepiness and alertness. 

The term circadian comes from the Latin circa, meaning "around" (or "approximately"), and diēm, meaning "day". The formal study of biological temporal rhythms, such as daily, tidal, weekly, seasonal, and annual rhythms, is called chronobiology. Processes with 24-hour oscillations are more generally called diurnal rhythms; strictly speaking, they should not be called circadian rhythms unless their endogenous nature is confirmed.

A circadian rhythm is any biological process that displays oscillation of about 24 hours. They are endogenous ("built-in", self-sustained), and they are adjusted (entrained) to the local environment by external cues called zeitgebers (from German, "time giver"), which include light, temperature etc. These 24-hour rhythms are driven by a circadian clock, and they have been widely observed in plants, animals, fungi, and cyanobacteria.

In 2017, the Nobel Prize in Physiology or Medicine was awarded to Jeffrey C. Hall, Michael Rosbash and Michael W. Young" for their discoveries of molecular mechanisms controlling the circadian rhythm" in fruit flies. The earliest recorded account of a circadian process dates from the 4th century BC, when Androsthenes, a ship captain serving under Alexander the Great, described diurnal leaf movements of the tamarind tree.

The Science behind it

Every person has a built-in biological clock, which is responsible for regulating the timing of many biological functions, such time to sleep and time to eat. The Circadian rhythms within our biological clock manage daily cycles such as sleeping and waking, contributing to how much energy we have at given points throughout the day. The so-called “master clock” governing human and other mammalian circadian rhythms is the suprachiasmatic nucleus (SCN), a pair of cell populations packed with genes and located in the hypothalamus that carry out this function. Destruction of the SCN results in the complete absence of a regular sleep–wake rhythm.

The SCN receives information about illumination through the eyes. Outside factors like lightness and darkness can thus impact the circadian rythm. When it’s dark at night, our eyes send a signal to the hypothalamus that it’s time to feel tired. Our brain, in turn, sends a signal to our body to release melatonin, which makes our body tired. The SCN takes the information on the lengths of the day and night from the retina, interprets it, and passes it on to the pineal gland, a tiny structure shaped like a pine cone and located on the epithalamus. In response, the pineal secretes the hormone melatonin. Secretion of melatonin peaks at night and ebbs during the day and its presence provides information about night-length. That’s why our circadian rhythm tends to coincide with the cycle of daytime and night time (and why it’s so hard for shift workers to sleep during the day and stay awake at night). Not only sleep but mental alertness, hunger, stress, mood, heart function, and even immunity are also influenced by the body's daily rhythms.

Our circadian clock sets the rhythm for our cells’ powerhouses, the Mitochondria. These are  small organelles that exist in almost all our cells and supply them with energy. The time of day determines the design of the mitochondrial network, and this, in turn, influences the cells' energy capacity.

So why is this important for us?

1.       Attentiveness and efficiency: By doing certain things at peak periods of energy and activity, there’s a chance we’ll be able to improve our productivity. Conversely when things get in the way of this rythm, like jet lag, daylight savings time, or a compelling sporting event on TV that keeps you up into the wee hours of the morning, we can disrupt our circadian rhythm, which makes us feel out of sorts and can make it harder to pay attention. 

2.       Professions: Shift-work or chronic jet-lag have profound consequences on circadian and metabolic events in the body. Due to the work nature of airline pilots, who often cross several time zones and regions of sunlight and darkness in one day, and spend many hours awake both day and night, they are often unable to maintain sleep patterns that correspond to the natural human circadian rhythm; this situation can easily lead to fatigue. The NTSB cites this as contributing to many accidents and has conducted several research studies in order to find methods of combating fatigue in pilots.

3.       Thinking and learning: This differs for many people, however as a general rule, we tend to be sharpest in the morning. Studies suggest that we tend to be at the height of our cognitive power during the late morning, so you might want to tackle any mentally-taxing activities you need to do before lunchtime.

4.       Inattentive after meals: Alertness and attention levels wane after eating a meal. That’s why we’re likely to find it harder to concentrate at work after we’ve had your lunch. Concentration levels dip the most between noon and 4 pm. In fact, many people find themselves in need of an energy-boosting pick-me-up during those hours. So eating times can also play a role in resetting our biological clock. Altering our eating schedule can also help you to reset your body clock to match a new daily routine.

5.       Metabolic diseases like Diabetes: Animals that are forced to eat during their resting period show increased body mass and altered expression of clock and metabolic genes. Obesity and diabetes are associated with lifestyle and genetic factors. Among those factors, disruption of the circadian clockwork and/or misalignment of the circadian timing system with the external environment (e.g., light-dark cycle) might play a role in the development of metabolic disorders.

6.       Sleeping habits and siesta time:  As our biological clock plays a major role in controlling our sleep-wake cycle, our schedule, bedtime routines, and even our age can also play a role in affecting the cycle. The body’s natural sleep-wake cycle changes as we age. As people approach later adulthood, their cycle tends to shift toward rising early in the morning. In fact, it’s quite common to see older adults that prefer to go to bed earlier and get up earlier. As most people’s energy levels take a dip in the early afternoon, it’s a great time to take a nap. Even if you’re not able to take one due to work commitments or otherwise, taking a quick break from what you’re doing might be beneficial.

7.       Jet-lag: travelers may experience disturbances to their sleep-wake cycles that lead to a feeling of jet lag

Tips for Adjusting

In spite of the fact that everyone’s biological clock functions differently, here are some tips for establishing a more productive daily schedule:

•   Establish a sleep schedule: Set an alarm and go to bed at the same time each night. Wake up when your alarm goes off—no hitting that snooze button over and over again.

•   Give it some time: Getting used to a new schedule may take a while, but stick with it until it starts to feel more natural.

•   Pay attention to your energy levels: Try to arrange certain activities around your peak energy levels. Not everyone is the same, so your own energy levels may follow a slightly different schedule.

Circadian rhythm in animal world

Circadian rhythms allow organisms to anticipate and prepare for precise and regular environmental changes. They thus enable organisms to better capitalize on environmental resources (e.g. light and food) compared to those that cannot predict such availability. The circadian rhythms thus puts certain organisms at a selective advantage in evolutionary terms. However, rhythmicity appears to be as important in regulating and coordinating internal metabolic processes, as in coordinating with the environment. Norwegian researchers at the University of Tromsø have shown that some Arctic animals (ptarmigan, reindeer) show circadian rhythms only in the parts of the year that have daily sunrises and sunsets. In one study of reindeer, animals at 70 degrees North showed circadian rhythms in the autumn, winter and spring, but not in the summer. Reindeer on Svalbard at78 degrees North showed such rhythms only in autumn and spring. The researchers suspect that other Arctic animals as well may not show circadian rhythms in the constant light of summer and the constant dark of winter.

Circadian rhythm in the plant world

Plant circadian rhythms tell the plant what season it is and when to flower for the best chance of attracting pollinators. Behaviors showing rhythms include leaf movement, growth, germination, stomatal/gas exchange, enzyme activity, photosynthetic activity, and fragrance emission, among others. A better understanding of plant circadian rhythms has applications in agriculture, such as helping farmers stagger crop harvests to extend crop availability and securing against massive losses due to weather.