“Everything has a season, and time for every matter

A time to be born, a time to die,

A time to plant and a time to pluck up what is planted,

A time for sleep and a time for wake up,

God has made everything beautiful in its time”

For millions of years, the only source of light was the sun, and humans followed a natural cycle of day and night. However, changes in this milieu began approximately 150 years ago with the invention of artificial lighting.

A number of new research focus on the physiologic outcomes of artificial light exposure and the subsequent adaptations of our circadian rhythms.

Circadian rhythms are the biological processes that show endogenous and also entrainable oscillations of around 24 hours in our bodies.

Almost all living organisms including plants, animals, microbes, have circadian rhythms. There is an entire field dedicated to the study of circadian rhythms called chronobiology.

Substantial evidence suggests that disturbances in the circadian rhythms are a significant risk factor for many health problems including cardiovascular diseases, metabolic disorders, accelerated ageing, and impaired immune functions.

Restoring and strengthening the circadian rhythm may prove to be a strong therapeutic factor for optimising our health.

The severity and also the incidence of many diseases such as the onset of cardiovascular problems, inflammatory diseases, chronic obstructive pulmonary disease (COPD), rheumatic conditions, and mental problems are all time-dependent.

In prehistoric times, men went to river banks in the forest to hunt in the wee hours of the morning as this was when the animals emerged to drink water.

This time, therefore, was associated with mental stress and physical exertion with an underlying biochemical storm of cortisol hormone being released early in the morning.

Back then there was no artificial light. The only source of light was the sun, and at night, there was only the dim moonlight. And so, there was the one-time secretion of melatonin and cortisol hormones in sync with the light and darkness cycle, resulting in a set time of sleep and waking behaviour.

Today, the modern world has disrupted this natural rhythm. Hence, jetlag causing long flights across continents, erratic working hours, night shifts, and other lifestyle changes trigger our internal natural cycle and greatly impact the functioning of the circadian rhythm.

There is a master clock in the brain called the suprachiasmatic nucleus (SCN). This master clock receives light signals from the retina of the eye and sends this information to various parts of the brain, including the pineal gland that releases melatonin hormone.

However, these signals vary throughout the day; this is the reason why our circadian rhythm typically coincides with the sun’s cycle. At night, our SCN receives signals for darkness. This causes it to send a message to the brain that it’s time to release melatonin, which makes us sleepy.

The opposite occurs during the daytime because light signals suppress the production of melatonin.

This study of the body clock and its impact on one’s health is so significant that in 2017, Jeffrey Hall and Michael Rosbash of Brandeis University and Michael Young of Rockefeller University received the Nobel Prize in Physiology and Medicine, for their discovery on how time is measured each day in the biological system which also includes one’s own bodies.

Now it has been widely accepted that the central role of circadian rhythms is to coordinate an organism`s life with a day and night cycle. And it controls everything from metabolism to sleep time.

Hormones like melatonin and cortisol are the major circadian rhythm hormones.

Melatonin is a night hormone that is responsible for sleep. Whereas cortisol is a hormone that makes us more alert, and our body produces more of it during the day.

Melatonin, secreted by the Pineal Gland, is one of the major signaling molecules used by the master circadian oscillator to entrain circadian rhythms. Its secretion is affected by factors such as light, age, physiological and environmental factors.

Usually, melatonin levels begin to increase late in the evening, remain raised in the greater part of the night, and start decreasing at around dawn.

Melatonin has been shown to have analgesic effects and it’s also effective in reducing symptoms of many pain disorders.

Metabolism and body temperature are also part of our circadian rhythm:

• During sleep, the body temperature drops and rises during wake hours.

• Additionally, the metabolism system of our body works at different rates throughout the day.

• Age is another factor that influences circadian rhythm. Infants, teens, and adults all experience circadian rhythms differently.

• Other factors may also influence the circadian rhythm. For instance, the rhythm gets adjusted based on our working hours, physical activity, and additional habits or lifestyle choices.

Sometimes, going against our circadian rhythm can cause adverse effects to our bodies as it creates a clash between our disturbed lifestyle and our internal biological clock system.

This could occur because of:

1. Working overnight that goes against nature’s light and dark time

2. Erratic working hours and shifts

3. Constant travel in different time zones

4. Lifestyle that encourages late-night hours or early waking times

5. Stress

6. Poor sleep habits, including the lack of a sleeping schedule

7. Watching television or using your mobile phone at bedtime

• Maintain a consistent sleep schedule

Melatonin hormone usually begins to trigger the body to rest around 9 PM and starts slowing down (cueing the body to wake up) around 7:30 AM.

And so it's important we try and adhere to our sleep schedule around these times every day. If your routine is drastically different from these times, you might not be able to adjust it right away, but try to do it slowly in increments of 15 minutes, every few days.

• Spend time outdoors

Another important point is to spend time outdoors when it’s light outside to boost wakefulness as exposure to sunlight will help reset the internal clock for the day.

• Skip the afternoon nap

Staying active throughout the day can help balance circadian rhythm by using energy stores before your sleeping hours.

If you have trouble sleeping, taking a nap can decrease the ability to fall asleep at night. So, it's better to be awake for longer hours, so it would be easy for the body to sleep toward the end of the day.

• Avoid heavy meals and caffeine later in the day

Whatever a person eats can impact their sleep. Heavy food and alcohol cause heartburn, and caffeine is a stimulant that triggers the brain to keep the body active.

Go easier on your liver by making it a point to eat before 7 PM in order. At night our body’s master clock triggers the release of melatonin and it sends signals to the liver to stop creating enzymes that turn calories into energy, and instead begin storing that energy.

• Limit the use of a screen at night

The blue light from the laptop and mobile phone's screen can trick the brain into thinking it’s still daytime, causing it to suppress melatonin secretion and delay in sleep.

If using your phone at night is unavoidable, at the very least, start dimming its lights two hours before bedtime, in order to get better on-time melatonin secretion and a sound sleep.

(Dr Ghizal Fatima is Assistant Professor, Department of Biotechnology, Era University, Lucknow. Her areas of works include biomedical research, chronobiology & nutritional sciences.)

(Dr Faiz Abbas Abidi is a junior doctor at Era Hospital working on biomedical research, public health issues and digital health interventions. Dr Faiz is working on ICMR supported project on Circadian rhythm and its association with cardiovascular diseases . Tweets at @doc_faiz.)