Sunlight affects hormones and sleep, specifically the circadian rhythm.

Question

Think about the ideas in the two passages, and then write an explanatory essay that explains the connection among light, hormones, and sleep.

Be sure to use information from BOTH texts in your explanatory essay. Write your answer in the space provided.

Before you write, be sure to:

• think about ideas, facts, definitions, details, and other information and examples you want to use;
• think about how you will introduce your topic and what the main topic will be for each paragraph;
• develop your ideas clearly and use your own words, except when quoting directly from the source texts;
• be sure to identify the sources by title or number when using details or facts directly from the sources.

Now write your explanatory essay in the space provided. Be sure to:

• use information from the two texts so that your essay includes important details;
• introduce the topic clearly, provide a focus, and organize information in a way that makes sense;
• develop the topic with facts, definitions, details, quotations, or other information and examples related to the topic;
• use appropriate and varied transitions to create cohesion;
• clarify the relationships among ideas and concepts;
• use clear language and vocabulary to inform about the topic;
• provide a conclusion that follows the information presented; and
• check your work for correct grammar, usage, capitalization, spelling, and punctuation.

PASSAGE 1: Melatonin and Sunlight

By Priyanka Walker

When the Sun sets on the horizon, cities around the globe slow down, people begin to yawn, and bedtime ensues. In contrast, when the Sun rises, the world repeatedly wakes. What causes this consistent sleep and wake cycle that coincides with dawn and dusk? Is it simply a universal human habit that most people continue to do because everyone else is doing it? No, it’s not a habit or a tradition handed down from our great-grandparents’ great-grandparents. Like many things, science explains that our tendency to follow this pattern is deeply rooted in both our physiology and our body’s connection to its environment. Our desire to sleep when it’s dark and to rise when it’s light is due to a complex and fascinating phenomenon called the circadian rhythm, a twenty-four-hour cycle connected to our exposure to sunlight as well as the activation of several hormones within us.

To understand circadian rhythm, one has to first understand melatonin, the sleep hormone. Hormones are the chemical messengers our body uses to initiate activity in various anatomical systems. In this case, the hormone melatonin triggers our bodies to transition into sleep mode, and then the hormone continues to be produced for several hours each evening, reminding several of our bodily systems to remain in resting state.

Melatonin is released from tissue all over the body, but the primary producer of this sleepy-time hormone is a part of the brain called the pineal gland. The pineal gland usually starts producing melatonin around 9 p.m. as long as it is uninhibited by human routines such as nightshift schedules, bright light, or travel to different time zones (also known as “jet lag”). Melatonin levels at night in a healthy human are typically ten times what they are during the day. It’s no wonder that it can be extremely difficult to fight off sleep at night—there’s an entire army of hormones at work.

When this blast of nighttime melatonin takes place in the pineal gland, it uses the circulatory system to carry melatonin through the blood to various parts of the body that have melatonin receptors. When these receptors receive melatonin, they respond in a variety of ways. For example, the heart rate slows and the body temperature lowers which both encourage relaxation so that sleep takes place. Eventually, melatonin stops being released (it is typically sometime around 6:30 a.m.), and these same body systems start waking up. Later in the day, the process repeats itself again starting with the melatonin release from the pineal gland.

Clearly, melatonin is tightly linked to our circadian rhythm, but what causes the pineal gland to kick into action and start releasing melatonin? You probably guessed it—it’s the Sun that triggers this entire process. Sunlight hits our eyes, and even more specifically, it hits the retina. It may surprise you to find out that our eyes are actually a part of the brain—a very important part at that! Your retina, the innermost lining of the eye, takes in visual information and sends it to other parts of the brain using the optic nerve. In this case, the optic nerve prompts the pineal gland to get to work releasing melatonin. This connection of sunlight to the release of melatonin is crucial to keeping us on a healthy sleep schedule.

PASSAGE 2: Impact of Blue Light on Sleep

By Tyler Jackson

If you have ever been on a beach at sunset, you may have noticed that crowds gather with quiet reverence to watch the Sun lower in the distance. Interestingly, the quiet reverence may not simply be due to the beauty of the moment, but it might be because at sunset our eyes detect a specific type of sunlight which sets off an array of activity within our bodies that notify all the necessary systems that it is time to sleep. Likewise, at dawn as the Sun rises, this same light, blue light, reaches our eyes. Blue light is an integral part of maintaining our circadian rhythm, but too much of it at the wrong time can cause sleep problems.

According to health.ucdavis.edu, “Blue light is part of the visible light spectrum—what the human eye can see…it has the shortest wavelength and highest energy. About one-third of all visible light is considered high-energy visible, or ‘blue,’ light. Sunlight is the most significant source of blue light. Artificial sources of blue light include fluorescent light, compact fluorescent lightbulbs, LEDs, flat screen LED televisions, computer monitors, smart phones and tablet screens.” In 1981, Dr Charles Czeisler of Harvard Medical School showed that a person’s circadian rhythm is aligned with the environment specifically because of the blue light in daylight, but scientists are now discovering that an excessive amount of artificial sources of blue light contribute to sleep disturbances.

Blue light from the Sun is especially prevalent at dawn and dusk because it emerges when the Sun is 4-8 degrees below the horizon. Without a person knowing it, his or her retina detects these blue light rays, and by way of the optic nerve, it lets the body know that the blue light of dawn has arrived. This causes the production of melatonin to stop, and the body’s systems that were in sleep-mode begin to awaken. Later, as the Sun sets, our eyes take in the blue light again, but this time rather than stopping the production of melatonin, it encourages it, making us ready for sleep.

For centuries, our bodies and our melatonin flowed to the rhythm of the Sun, but the advent of the lightbulb and artificial light complicated our bodies’ relationship with the natural rhythms that regulated our sleep. Bright lights confuse our bodies into thinking it’s time to be awake and we often don’t get the rest our body needs. Researchers have found that bright overhead lights are especially disruptive to our sleep patterns. Lighting placed at a lower height tends to have less impact on our circadian rhythm, and one study showed that using candlelight causes no disruption to our melatonin production. Scientists are still researching and learning about how the blue light emitted from computer screens and smart phones affects our sleep patterns. The current findings suggest that screens are an intense form of blue light and are especially toxic to our circadian rhythm. Studies show that exposure to blue light from artificial light sometimes suppresses the release of melatonin for several hours.

Answer 1

The Connection Among Light, Hormones, and Sleep

The intricate interplay between light, hormones, and sleep is vital for maintaining a healthy circadian rhythm, which is our body’s internal clock that regulates sleep-wake cycles. As denoted in both passages by Priyanka Walker in "Melatonin and Sunlight" and Tyler Jackson in "Impact of Blue Light on Sleep," this relationship is fundamentally rooted in our biology and the environment around us. The primary focus of this essay is to elucidate how sunlight triggers hormonal changes in the body, specifically the production of melatonin, which in turn dictates our sleep patterns.

At the core of the circadian rhythm is the hormone melatonin, often referred to as the sleep hormone. Walker emphasizes that melatonin is primarily produced in the pineal gland as night falls. When the sun sets and darkness prevails, the pineal gland releases melatonin into the bloodstream, signaling to the body that it is time to rest. This release of melatonin results in physical changes that promote relaxation, such as a decrease in heart rate and body temperature, thereby facilitating the transition into sleep. The cycle continues, with melatonin levels decreasing in the morning as sunlight exposure increases, allowing the body to awaken and resume its daytime functions. This natural ebb and flow of melatonin is harmonized with the rising and setting of the sun, exemplifying the biological grasp of the human body on environmental light conditions.

Furthermore, Jackson addresses the vital role of specific wavelengths of light, particularly blue light, in regulating the production of melatonin. Blue light, abundant in sunlight, reaches our retina and is crucial in signaling the body about the time of day. At dawn, the presence of blue light halts the production of melatonin, effectively waking the body from its sleep state. Conversely, as daylight fades and the blue light diminishes, melatonin production resumes, encouraging us to prepare for sleep. This delicate balance between light exposure and hormonal response underscores the importance of natural light in synchronizing our internal biological clock.

However, the introduction of artificial light has disrupted our natural circadian rhythm. Jackson notes that exposure to artificial blue light from modern devices—such as smartphones and LED screens—can lead to significant sleep disturbances. This form of high-energy visible light can suppress melatonin production for hours, confusing the body into thinking it is still daytime, and ultimately delaying sleep onset. The erosion of our body’s natural responses to light due to artificial illumination poses a growing concern in the modern era, highlighting the need for awareness of how light exposure relates to sleep health.

In conclusion, the relationship among light, hormones, and sleep is both profound and complex. Sunlight governs our production of melatonin, which orchestrates our sleep-wake cycles through intricate hormonal processes. However, while natural light reinforces this connection and keeps our circadian rhythm intact, artificial light presents challenges that can disrupt our sleep patterns. Awareness of these dynamics can empower individuals to cultivate healthier sleep habits by moderating exposure to artificial light, particularly in the evening. Ultimately, understanding the interplay of light and hormones is crucial for promoting better sleep and overall well-being.