Chasing the Sun

Chasing the Sun Plot Summary

Introduction

Have you ever noticed how your mood lifts on a sunny day, or how much better you sleep after spending time outdoors? These aren't coincidences - they're evidence of the profound relationship between sunlight and our bodies. For thousands of years, humans have worshipped the sun, structuring societies around its rhythms and celebrating its seasonal returns. Today, science is uncovering just how deeply our biology is intertwined with our nearest star. Our bodies evolved on a planet that rotates every 24 hours, creating predictable patterns of light and darkness. This daily cycle has shaped our internal biology so fundamentally that nearly half our genes operate on a daily rhythm. But modern life has disrupted this ancient relationship. We spend our days in dimly lit offices and our evenings bathed in artificial light from screens and bulbs. This mismatch between our evolutionary programming and current environment affects everything from our sleep quality to our mental health, immune function, and even our risk for diseases like cancer and diabetes. Understanding how sunlight shapes us doesn't just satisfy scientific curiosity - it provides practical insights that can help us sleep better, think more clearly, and live healthier lives in our modern world.

Chapter 1: The Body Clocks: Our Internal Timekeepers

Inside every cell of your body ticks a microscopic clock. These aren't actual timepieces with hands and gears, but rather collections of proteins that build up and break down in regular cycles, governing when cells perform various functions. These cellular timekeepers are orchestrated by a master clock in your brain - a tiny structure called the suprachiasmatic nucleus (SCN), located deep in the hypothalamus. Though only the size of a grain of rice, this remarkable brain region synchronizes billions of cellular clocks throughout your body. These internal timekeepers generate what scientists call circadian rhythms - from the Latin "circa" (around) and "diem" (day). They evolved because aligning our biology with the planet's rotation improved our ancestors' survival chances. When your circadian system is properly aligned with natural light cycles, it creates predictable patterns in your body temperature, hormone levels, alertness, and countless other functions. Your body temperature naturally peaks in late afternoon and reaches its lowest point in the early morning. Hormones like cortisol surge at dawn to wake you up, while melatonin rises after sunset to prepare you for sleep. The alignment of these rhythms affects nearly every aspect of health and performance. Athletic ability, cognitive function, immune response, and even wound healing all show distinct daily patterns. When researchers engineered mice with disrupted circadian clocks, they found these animals were more susceptible to disease and showed signs of premature aging. Your circadian system is so important that in 2017, the Nobel Prize in Medicine was awarded to scientists who uncovered the molecular mechanisms of these biological clocks. What synchronizes these clocks with the outside world? Primarily light, especially morning sunlight. Special cells in your retina called intrinsically photosensitive retinal ganglion cells (ipRGCs) detect light and send signals directly to your brain's master clock. These cells are particularly sensitive to blue wavelengths found in morning sunlight. When this blue-rich light hits your eyes, it resets your master clock, which then signals to all your cellular clocks that it's daytime. This explains why morning light exposure is so effective at regulating sleep patterns and why evening exposure to blue light from screens can disrupt sleep. Most people's internal clocks run slightly longer than 24 hours - closer to 24.2 hours on average - which means that without environmental cues like sunlight, we would gradually drift later and later each day. This is what happens when people participate in isolation experiments in underground bunkers with no time cues. Their sleep-wake cycles begin to "free-run" on their internal rhythm. Only through daily resetting by sunlight do our clocks stay synchronized with the 24-hour day. In our modern environment, with insufficient daylight exposure and excessive evening light, many people experience "social jet lag" - a mismatch between their internal clock and social schedule. This contributes to sleep problems, mood disorders, metabolic dysfunction, and even increased risk for serious diseases. Understanding your own circadian tendencies - whether you're naturally a "morning lark" or "night owl" - and aligning your life with these patterns where possible can dramatically improve your health and wellbeing.

Chapter 2: Modern Light vs. Natural Rhythms: A Disrupted Balance

Until about 150 years ago, humans lived in a world where daylight meant activity and darkness meant rest. The introduction of gas lighting in the early 1800s, followed by Edison's practical electric light bulb in 1879, fundamentally altered our relationship with light and darkness. Before electric lighting, people typically slept in two distinct segments - a "first sleep" shortly after sunset, followed by a wakeful period of an hour or two, then a "second sleep" until dawn. This pattern disappeared as artificial lighting extended our days. Modern homes and workplaces create a light environment vastly different from what our bodies evolved to expect. The average office provides only about 300 lux of illumination - a measure of light intensity - while a cloudy day outdoors delivers at least 3,000 lux, and direct sunlight can reach 100,000 lux. Meanwhile, our evenings are now filled with artificial light from ceiling fixtures, televisions, and the blue-wavelength light from computer screens and smartphones. This creates a flattened light exposure pattern where we get too little light during the day and too much at night. Our bodies interpret light signals according to rules established over millions of years of evolution. When light enters our eyes, particularly blue-wavelength light, it suppresses the production of melatonin, the hormone that signals to our body that it's nighttime. This made perfect sense in our evolutionary past - when the sun was up, melatonin was suppressed; when darkness fell, melatonin was released, preparing us for sleep. But now, evening exposure to blue-rich light from screens and LED lighting delays this natural melatonin release, making it harder to fall asleep and reducing sleep quality. Research has demonstrated the serious consequences of this disrupted light-dark cycle. A study at the University of Colorado sent participants camping for a week with no artificial light sources. After just seven days in natural light conditions, their internal clocks shifted nearly two hours earlier, and melatonin began rising at sunset rather than hours later. Other studies have shown that insufficient daytime light exposure combined with evening light pollution can reduce sleep quality, impair alertness, worsen mood, and even affect metabolic health by disrupting the timing of hunger hormones. The implications extend beyond just feeling tired. Our cells perform different functions depending on the time of day - DNA repair happens primarily during nighttime hours, while cell division occurs mostly during the day. Immune function, hormone production, and even gene expression follow daily patterns governed by our circadian system. When these patterns are disrupted by inappropriate light exposure, our bodies can't perform these functions optimally, potentially contributing to increased rates of cancer, diabetes, obesity, and depression in modern society. The good news is that being mindful about light exposure can help restore healthier patterns. Getting bright light exposure in the morning, spending time outdoors during daylight hours, dimming lights in the evening, and using blue-light blocking technology at night can help realign our internal clocks with natural rhythms. Many people report improved sleep, mood, and energy levels when they make these simple adjustments to their light environment.

Chapter 3: Shift Work and Circadian Misalignment: Health Consequences

Nearly 20 percent of the global workforce engages in shift work, keeping our hospitals, factories, transportation systems, and emergency services running around the clock. While this arrangement provides essential services, it creates a profound mismatch between these workers' internal biological rhythms and their work schedules. This mismatch, called circadian misalignment, has been linked to serious health consequences. When you work at night and attempt to sleep during the day, you're fighting against your body's fundamental programming. The circadian system sends strong alerting signals during daylight hours and promotes sleep at night. Even experienced night shift workers rarely achieve complete adaptation to their schedules. Their core body temperature, hormone levels, and alertness patterns remain partially tied to the solar day rather than their work schedule. This creates a state of internal confusion where different systems in the body run on different time schedules. The health impacts of this misalignment are becoming increasingly clear. In 2007, the International Agency for Research on Cancer classified shift work that disrupts circadian rhythms as a "probable carcinogen" after reviewing evidence linking it to increased breast cancer risk. Beyond cancer, shift workers face higher rates of cardiovascular disease, with studies showing a 40% increased risk of heart disease among those who work nights. Metabolic disruptions are also common - shift workers have higher rates of obesity, diabetes, and metabolic syndrome than day workers in the same jobs. One key mechanism behind these health effects involves how circadian disruption affects metabolism. In a groundbreaking study, researchers had healthy volunteers follow a protocol that gradually shifted their sleep times until they were completely misaligned with their internal clocks. After just ten days, participants showed dramatic metabolic changes - including insulin resistance similar to pre-diabetes and disruptions in hormones that regulate hunger and satiety. These same mechanisms likely contribute to the higher rates of obesity and diabetes seen in shift workers. Cognitive performance also suffers during night shifts. Alertness and decision-making abilities reach their lowest point between 2 a.m. and 6 a.m., coinciding with the nadir in core body temperature. This performance drop explains why catastrophic industrial accidents like Chernobyl, Three Mile Island, and the Exxon Valdez oil spill all occurred during night shifts. For shift workers in critical positions - like medical staff, pilots, or nuclear plant operators - these cognitive deficits can have life-or-death consequences. While eliminating shift work isn't realistic in our 24/7 society, certain strategies can mitigate its negative effects. Stable shift schedules are less disruptive than rotating ones. Strategic exposure to bright light during shifts and wearing blue-blocking glasses on the commute home can help regulate melatonin. Maintaining regular meal timing rather than eating throughout the night shift may help preserve metabolic health. Some organizations are implementing these insights by redesigning lighting systems and work schedules to better support their shift workers' biological needs, potentially improving both health outcomes and workplace safety.

Chapter 4: Sunlight as Medicine: From Vitamin D to Immune Function

The healing power of sunlight has been recognized since ancient times. Hippocrates, the father of modern medicine, recommended sunbathing for restoration of health and built a large solarium for his patients. Ancient Egyptian healers used sunlight combined with plant extracts to treat skin diseases - a therapy remarkably similar to modern photodynamic treatments. These early practitioners didn't understand the mechanisms behind sunlight's healing properties, but they recognized its effectiveness. In the late 19th century, scientific investigation of sunlight's medical benefits began in earnest. In 1903, Niels Ryberg Finsen won the Nobel Prize for developing light therapy to treat tuberculosis of the skin (lupus vulgaris), a disfiguring condition that had previously been incurable. By filtering and concentrating ultraviolet rays through quartz lenses, Finsen successfully treated hundreds of patients who had failed to respond to other treatments. This sparked a medical revolution, with "heliotherapy" (sun therapy) becoming widely prescribed for various conditions throughout the early 20th century. The most dramatic example of sunlight's healing power emerged through the discovery of vitamin D. In the 1800s, rickets - a bone-deforming disease caused by vitamin D deficiency - affected up to 90% of children in some industrial cities. The connection between sunlight deprivation and rickets was first recognized by Theobald Palm, an English physician who noticed the disease was virtually absent in sunny countries regardless of poverty levels, yet rampant in prosperous but sun-deprived industrial cities. Scientists eventually discovered that ultraviolet rays from sunlight trigger vitamin D production in the skin, which is essential for calcium absorption and bone development. Today, we understand that vitamin D receptors exist throughout the body - in the brain, heart, immune cells, and more - suggesting its influence extends far beyond bone health. Modern research continues to uncover sunlight's therapeutic potential. Ultraviolet light therapy remains a standard treatment for psoriasis, eczema, and other inflammatory skin conditions. Beyond skin conditions, emerging evidence suggests sunlight exposure may help regulate immune function and reduce inflammation throughout the body. When UV light hits the skin, it triggers the release of specialized immune cells that help maintain a balanced immune response. This may explain why conditions like multiple sclerosis show a striking latitude gradient, becoming more common the further people live from the equator. Perhaps most surprisingly, sunlight appears to influence cardiovascular health through mechanisms separate from vitamin D. When sunlight hits the skin, it releases stores of nitric oxide, a molecule that dilates blood vessels and lowers blood pressure. This effect occurs within minutes of sun exposure and may help explain why blood pressure tends to be lower in summer months and in regions with more sunlight. Some studies have even found that regular, moderate sun exposure is associated with reduced mortality rates despite the increased skin cancer risk. The emerging picture suggests a complex relationship between sunlight and health that extends beyond vitamin D. While excessive sun exposure increases skin cancer risk, complete sun avoidance may create its own health problems. The challenge for modern health science is determining the optimal balance - enough sunlight to receive its health benefits while minimizing the risk of skin damage and cancer.

Chapter 5: Seasonal Moods: Understanding Winter Depression

As daylight shortens and temperatures drop with the approach of winter, many people experience a distinct shift in their mood and energy levels. For most, this manifests as a mild case of the "winter blues" - feeling a bit more tired, craving carbohydrates, and perhaps becoming less sociable. But for about 5-10% of people in northern latitudes, these symptoms intensify into a clinical condition called Seasonal Affective Disorder (SAD). Unlike general depression, SAD follows a predictable seasonal pattern, typically beginning in autumn as days shorten and resolving in spring when daylight increases. Its symptoms include not only low mood but also excessive sleepiness, increased appetite (particularly for carbohydrates), weight gain, and a heavy, leaden feeling in the arms and legs. The condition is markedly more common at higher latitudes with shorter winter days. In Florida, about 1% of the population experiences SAD, while in Alaska, the rate jumps to nearly 10%. The scientific understanding of SAD began in the early 1980s when researcher Norman Rosenthal and colleagues at the National Institute of Mental Health identified the condition. They discovered that many people with winter depression responded dramatically to treatment with bright artificial light. This observation led to the development of light therapy as the first-line treatment for SAD. Typically, patients sit in front of a specialized light box providing 10,000 lux of broad-spectrum light for 30-45 minutes each morning. Studies show this treatment is as effective as antidepressant medications for many people with SAD. What causes this seasonal mood shift? The leading theory involves how changing light patterns affect our internal clocks and key neurotransmitters. As days shorten, people with SAD appear to experience a phase delay in their circadian rhythms - their internal biological clocks drift later relative to the external clock. This misalignment means they're often still in "biological night" when they need to wake up for work or school, contributing to morning grogginess and depression. Additionally, the neurotransmitter serotonin, which helps regulate mood, naturally decreases during winter months, with this effect being more pronounced in people with SAD. Light therapy works by resetting the circadian clock and boosting serotonin levels. Morning light exposure suppresses melatonin (the sleep hormone) and signals to the brain that it's daytime, helping to advance the circadian clock to better align with social schedules. Regular morning light exposure also appears to increase serotonin availability in the brain, improving mood. For many people with SAD, combining light therapy with getting outdoors when possible, regular exercise, and maintaining social connections provides significant relief. Interestingly, cultural attitudes toward winter may also influence how we experience the season psychologically. Research in northern Norway, where winter brings months of polar darkness, found surprisingly low rates of seasonal depression. Interviews with residents revealed a mindset that embraced winter as a special, cozy time rather than something to be endured. They used terms like "koselig" (the Norwegian version of the Danish "hygge") to describe the warm, intimate atmosphere created by candles, fireplaces, and gatherings with friends during dark winter evenings. This suggests that while the biological effects of reduced light are real, our psychological approach to winter can either amplify or mitigate these effects.

Chapter 6: Optimizing Light Exposure: Strategies for Modern Life

Creating a healthier relationship with light doesn't require moving to a tropical paradise or abandoning modern technology. Strategic adjustments to your daily light exposure can significantly improve your sleep, mood, and overall health. The key is maximizing the contrast between your daytime and nighttime light environments to send clear signals to your circadian system. Morning light exposure is arguably the most powerful tool for regulating your body clock. Aim to get bright light, preferably natural sunlight, within the first hour after waking. This morning light suppresses lingering melatonin, increases alertness, and sets your circadian rhythm for the day. Even on cloudy days, outdoor light is significantly brighter than indoor lighting - typically 1,000 to 10,000 lux compared to the 300-500 lux found in most offices. If you can't get outside, position yourself near a window or consider using a light therapy box that provides 10,000 lux of broad-spectrum light. Throughout the day, continue to seek natural light when possible. Take walking meetings, eat lunch outdoors, or position your desk near a window. Research shows that office workers with greater daytime light exposure report better sleep quality, less daytime dysfunction, and improved mood. For those with limited access to natural light, new circadian lighting systems that mimic the changing spectrum and intensity of daylight can help maintain healthier rhythms. These systems provide bright, blue-enriched light during daytime hours and gradually shift to warmer, dimmer light in the evening. As evening approaches, begin reducing light exposure, especially from blue-wavelength sources. Blue light has the strongest effect on suppressing melatonin and delaying the circadian clock. Dim household lights 2-3 hours before bedtime and consider using warm-colored bulbs (yellows and ambers) in evening lighting. For electronic devices, activate night mode features or wear blue-blocking glasses if you must use screens in the evening. Some research suggests that blue-blocking glasses worn for 2-3 hours before bed can improve sleep quality and increase melatonin levels by up to 58%. Your bedroom should be optimized for sleep with complete darkness during sleeping hours. Use blackout curtains if outside light enters your windows, and eliminate sources of light within the room, including LED indicators on electronics. If you need to get up during the night, use dim red night lights rather than turning on regular lights, as red wavelengths have minimal impact on melatonin and circadian rhythms. Seasonal adjustments may also be beneficial, particularly during winter months. When daylight hours shorten, make a special effort to get outside during daylight, even on cloudy days. For those experiencing winter blues or seasonal depression, morning light therapy has proven highly effective. A typical regimen involves 30 minutes of exposure to a 10,000 lux light box shortly after waking. Travel across time zones creates another circadian challenge. Jet lag occurs because your internal clock remains synchronized to your departure time zone while your body is physically in a new time zone. Strategic light exposure can accelerate adjustment: when traveling eastward, seek morning light and avoid evening light to advance your clock; when traveling westward, seek evening light and avoid morning light to delay your clock. This approach can reduce recovery time from jet lag by 50% or more.

Chapter 7: The Chronocity Vision: Designing Society Around Our Clocks

Imagine a society where school schedules accommodate teenagers' biological tendency to sleep later, where work hours flex to match individual chronotypes, and where hospitals use circadian lighting to improve patient recovery. This vision is beginning to take shape in pioneering communities that are redesigning their institutions around human biology rather than arbitrary social conventions. Our current social schedules largely ignore biological timing. The standard 9-to-5 workday and early school start times create significant challenges for many people, especially adolescents and natural "night owls." During puberty, biological changes shift teenagers' internal clocks later by about two hours, making it difficult for them to fall asleep before 11 p.m. or wake refreshed before 8 a.m. Yet most American high schools start before 8 a.m., effectively requiring teens to function during their biological night. The consequences are severe - chronic sleep deprivation affects 70% of high school students, contributing to poor academic performance, increased risk of depression, and higher rates of car accidents. When schools have experimented with later start times, the results have been remarkably positive. In Minnesota, shifting high school start times from 7:20 a.m. to 8:30 a.m. resulted in improved attendance, decreased depression symptoms, and fewer disciplinary problems. More dramatically, a British school that moved start times from 8:50 a.m. to 10 a.m. saw illness-related absences drop by half and student performance dramatically improve. As this evidence accumulates, more school districts are implementing later start times, although resistance remains due to concerns about bus schedules, after-school activities, and childcare arrangements. Workplaces are also beginning to recognize the importance of circadian biology. Some companies now offer flexible scheduling that allows employees to work according to their natural chronotypes - with morning larks starting and finishing earlier, while night owls arrive and depart later. This approach not only improves employee wellbeing but can enhance productivity. Research shows that matching work schedules to individual chronotypes results in better cognitive performance, reduced errors, and higher job satisfaction. Some organizations are also redesigning their office lighting to provide brighter, blue-enriched light during daytime hours to enhance alertness and concentration. Healthcare facilities represent another frontier for chronobiology-informed design. Hospitals traditionally maintain constant lighting throughout the day and night, disrupting patients' circadian rhythms at a time when robust rhythms could support healing. Innovative hospitals are now installing circadian lighting systems that provide bright, blue-enriched light during the day and dim, warmer light at night. Early research suggests these systems may reduce delirium in intensive care patients, improve mood in psychiatric units, and accelerate recovery from surgery. Similarly, care homes for people with dementia have found that strengthening light-dark patterns can reduce nighttime wandering and improve sleep quality. Perhaps the most ambitious vision comes from Bad Kissingen, Germany, which has declared itself the world's first "chronocity." This initiative aims to redesign multiple aspects of city life around biological timing - from school and work schedules to healthcare delivery and public lighting. While still in its early stages, the project represents a radical rethinking of how society might be structured if we prioritized alignment with our biological rhythms rather than industrial-era conventions. The growing interest in chronobiology-informed design reflects a broader recognition that human health and wellbeing depend on harmonizing our social schedules with our biological ones. By respecting rather than overriding our internal clocks, we can create communities that support better sleep, improved mental health, enhanced cognitive performance, and potentially reduced rates of chronic disease. The chronocity vision suggests that the next frontier in public health may not involve new medications or medical technologies, but rather a more thoughtful alignment between how we organize our society and how our bodies naturally function.

Summary

Our relationship with sunlight is far more profound than most of us realize. From the microscopic clocks ticking in every cell to the broad seasonal shifts in our mood and energy, light shapes nearly every aspect of our biology. The mismatch between our evolutionary programming and modern light environments - too little bright light during the day, too much artificial light at night - disrupts the rhythms that have guided human health for millennia. This disruption contributes to poor sleep, mood disorders, metabolic dysfunction, and increased vulnerability to diseases ranging from cancer to dementia. The good news is that we can reclaim a healthier relationship with light through relatively simple adjustments. Morning sunlight exposure, daytime brightness, evening darkness, and seasonal light therapy can dramatically improve sleep quality, mental health, and physical wellbeing. On a broader scale, redesigning our schools, workplaces, and healthcare facilities to respect human circadian biology could transform public health. The question now is whether we can collectively recognize the importance of these biological rhythms and create communities that support rather than override them. What might education look like if it were synchronized with students' biological clocks rather than administrative convenience? How might our cities be redesigned to provide adequate daylight access while reducing light pollution at night? As research in chronobiology continues to advance, these questions invite us to reimagine our relationship with the sun and with the rhythms that have guided life on earth since its beginning.

About Author

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Linda Geddes

Linda Geddes is a London-based journalist writing about biology, medicine and technology. Born in Cambridge, she graduated from Liverpool University with a first-class degree in Cell Biology. She has worked as both a news editor and reporter for New Scientist magazine, and has received numerous awards for her journalism, including the Association of British Science Writers’ awards for Best Investigative Journalism. She is married with two young children, Matilda and Max. (from http://www.lindageddes.com/biography)

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