Chasing the Sun

Have you ever noticed how your mood brightens on a sunny day, or how sluggish you feel after a week of rain? In Chasing the Sun: The New Science of Sunlight and How It Shapes Our Bodies and Minds, Linda Geddes explores why this happens — and why, despite living in a world saturated with artificial light, we’re still biologically tethered to the rhythms of our ancient star. Her central argument is both simple and profound: sunlight doesn’t just illuminate the world — it orchestrates nearly every aspect of our physiology and psychology, from our sleep and immune systems to our mood, metabolism, and lifespan.

Geddes contends that our modern relationship with light is profoundly unbalanced. We spend our days inside, away from natural daylight, and flood our nights with blue-rich artificial light. The result is a society chronically out of sync with the solar cycle that shaped our evolution. Drawing on research in chronobiology, neuroscience, dermatology, and history, Chasing the Sun shows that this disconnection from sunlight may underlie many of the diseases and stresses of modern life — from depression to diabetes, obesity to insomnia, and even cancer.

Rediscovering Our Solar Connection

Geddes opens by transporting readers to the Mojave Desert — a landscape that makes vivid the extremes of our relationship with the sun: life’s dependence on its energy and the danger of its excess. From there, she builds an argument that the sun has not only shaped evolution on Earth but continues to govern our internal clocks. We are, in her words, ‘children of the sun.’ This relationship, forgotten amid our electric modernity, governs our hormonal cycles, brain chemistry, immune responses, and even our lifespan.

She describes how humanity’s fascination with the sun has ancient roots — from the solstice rituals at Stonehenge and Newgrange to the solar deities of Egypt, Greece, and the Americas. These ancient intuitions, she argues, were not misplaced: our biology is indeed designed to track the sun’s rhythms. The alternating cycles of light and darkness help regulate everything from when we sleep to how our cells repair DNA damage. But unlike our ancestors, we now live largely divorced from this natural oscillation.

How Modern Light Distorts Our Clocks

At the heart of Geddes’s argument lies a paradox: the same artificial light that has liberated us from darkness now enslaves our biology to a perpetual twilight. The electric light bulb — Thomas Edison’s great invention — extended our days and revolutionized productivity, but it also blurred the natural boundary between night and day. Today, we spend more than 90% of our waking hours indoors, bathed in dim, constant light by day and harsh blue light at night. This inversion dampens the strength of our circadian rhythms — the daily biological cycles that evolved to mirror the sun’s rise and fall.

Circadian misalignment, Geddes explains, is no small issue: nearly half our genes follow these daily rhythms, influencing everything from metabolism and immunity to mental health. When we ignore them, we invite disease. Through the stories of blind individuals with drifting sleep-wake cycles, night-shift workers suffering from metabolic syndrome, and even astronauts trying to manage 16 sunsets a day aboard the International Space Station, Geddes shows what happens when our ‘body clocks’ lose touch with the solar clock.

The Many Faces of Sunlight

But Chasing the Sun is more than a story of loss — it’s a rediscovery of light’s healing power. Geddes resurrects forgotten history: Florence Nightingale’s belief that hospital patients need “not just light, but direct sunlight,” and Niels Finsen’s ultraviolet light therapy that cured tuberculosis patients a century before antibiotics. She traces how sunlight fuels our skin’s production of vitamin D, nitric oxide, and endorphins, and how these molecules lower blood pressure, lift mood, and protect against autoimmune disease. The sun, long demonized as a carcinogen, turns out also to be a powerful immunoregulator and antidepressant.

From Scandinavian light rooms to the mirror-laden valley town of Rjukan in Norway that literally reflects sunlight into its dark streets, Geddes explores how modern societies are reclaiming light in surprising ways. She also examines its darker side — ultraviolet radiation’s link to skin cancer, the sleep deprivation epidemic, and the risks of synthetic replacements like vitamin D supplements or blue-light-heavy LEDs.

A New Light-Driven Lifestyle

Ultimately, Geddes’s message is both scientific and moral: to heal ourselves, we must relearn to live by the sun. She calls for reimagining how we design buildings, cities, and even work schedules to align with daylight. Just as ancient civilizations oriented their temples toward the solstice sunrise, she suggests our modern world must orient its rhythms toward the sun once again. Her travels — from Amish farms that live by candlelight to high-tech hospitals using circadian lighting systems — reveal practical ways we can recalibrate daily life to our biology.

“We evolved on a rotating planet, when day was day and night was night. It’s time to reconnect with those extremes.”

Spanning science, history, and personal experiment, Chasing the Sun ultimately reframes sunlight as a biological necessity rather than a mere environmental hazard. Geddes reminds us that our health depends on not just shielding ourselves from sunlight’s danger, but also embracing its power to nurture, balance, and heal. In this summary, we’ll explore how the sun governs sleep and mood, what happens when our circadian clocks derail, how sunlight shapes our health through vitamin D and immunity, and how society can realign itself with the rhythms of the natural world once again.

Geddes begins by examining the marvel of the circadian rhythm — the intrinsic 24-hour biological cycle that hums inside every human cell. Like the Earth itself, we are rotating systems, our internal clocks keeping time with the sun’s daily arc. This synchrony governs when we feel sleepy or alert, when our hormones surge or ebb, when immunity peaks, and when our body heals.

How the Body Tells Time

Each of us has clock genes that produce proteins oscillating through the day, forming biochemical pendulums. These cellular clocks are coordinated by a cluster of neurons in the brain called the suprachiasmatic nucleus (SCN), nestled deep in the hypothalamus — our biological Greenwich observatory. The SCN resets itself each morning when light hits special photoreceptor cells in our eyes, particularly sensitive to blue light. These cells, called ipRGCs, don’t help us see; they tell the brain what time it is. From there, the SCN orchestrates the body’s daily symphony: cortisol peaks in the morning to energize us, body temperature and alertness rise toward midday, and melatonin flows after dusk to nudge us into sleep.

When the Clock Breaks Down

Geddes illustrates the chaos of desynchronization through vivid case studies: Mark Galvin, whose non-24-hour sleep–wake disorder causes his body to run on a 25-hour day, slipping one hour later with each sunrise; the blind man Harry Kennett, whose body “free-runs” without light cues because he lost his eyes in a wartime explosion; and the teen whose hormones and phone screen light push his sleep later and later. Modern life, Geddes shows, mimics these disorders: screens, night shifts, and late-night lighting all distort our internal timekeeping, leaving most of us a little bit jet-lagged every day.

The Evolutionary Logic of Clocks

Even ancient microbes kept time. Geddes describes experiments with blue-green algae, where mutant strains with too-short or too-long biological days were outcompeted by those that matched the planet’s 24-hour cycle. Nature favors those who anticipate dawn and dusk. In humans, such rhythms enhance survival too — our strength, reaction speed, and immune defenses peak in daylight when we’re active; our healing and memory processes intensify at night when we rest. Without synchronized rhythms, chaos ensues: fatigue, metabolic dysfunction, and even a greater risk of Alzheimer’s disease, as the brain’s nightly “cleansing” process falters.

Our internal timekeeping, Geddes concludes, evolved to align our bodies with the natural solar rhythm. And every flick of an LED switch or late-night flight threatens that ancient harmony. If we want balanced sleep, robust health, and mental clarity, the first step is to rediscover the rhythm of light itself.

Before electricity, nights were truly dark. Geddes guides us through the light revolution — from candles and gas lamps to Edison’s incandescent bulb — showing how each technological leap changed not just how we lived but when. With the flick of a switch, the ancient divide between day and night collapsed.

The Birth of Artificial Day

Gaslight, first spreading in industrial Britain, turned night into day, birthing nightlife and evening productivity. By the late 1800s, Edison’s bulb extended these rhythms into homes worldwide. But where Victorians saw progress, Geddes sees the dawn of a biological experiment. Electric light exposed humanity to constant illumination — bright enough to suppress melatonin, dim enough to confuse the body’s sense of day. Today’s omnipresent screens and blue-rich LEDs deepen this confusion, disrupting our circadian rhythms far more than candlelight or firelight once did.

The Cost of Endless Light

The human body, Geddes explains, never adapted to perpetual brightness. Constant exposure to artificial light leads to fragmented sleep and weakens metabolic and emotional stability. She cites studies comparing Amish families — who live largely by gaslight and sunlight — with their electrified neighbors. The Amish, who rise with dawn and sleep soon after sunset, have lower rates of depression, obesity, and insomnia. Their daylight exposure averages thousands of lux higher than typical urban citizens. Simply put: we live our days in perpetual dimness and our nights in perpetual glow — a reversal of natural order.

Bringing Nature Indoors

Geddes shares her own experiment: living by candlelight for several weeks while maximizing daylight exposure. Within days, her sleep shifted earlier, her morning lethargy vanished, and she felt more cheerful and focused. These findings echoed controlled studies from chronobiologist Kenneth Wright, who sent volunteers camping without electronics and found their body clocks re-synced to natural solar time within a week. The lesson is strikingly clear: just as too much night light harms us, too little daylight leaves us biologically starved. Before optimizing our sleep routines, she suggests, we must first optimize our light diet.

What happens when human ambition outpaces the sun? Geddes examines the 24-hour economy through one of its toughest experiments — night-shift workers, submariners, and astronauts. She shows how our pursuit of round-the-clock productivity conflicts with biology’s demand for rest, triggering widespread health costs.

When Time Becomes Toxic

Submarine commander Seth Burton describes working eighteen-hour days beneath the sea, cut off from sunlight. His crew cycled through artificial lighting that never matched Earth’s 24-hour rhythm, leaving men pale, stressed, and ill. Many developed insomnia, fatigue, and disease over time. Burton himself survived an aggressive cancer, which he suspects was linked to decades of circadian disruption. Scientists now agree: shift work is a probable carcinogen, confirmed by the World Health Organization in 2007. Disrupted melatonin, hormone imbalance, and derailed cell-repair cycles make chronic night work biologically hazardous.

Metabolic Chaos

Beyond fatigue, circadian misalignment wreaks havoc on metabolism. Researchers at Brigham and Women’s Hospital in Boston found that even well-rested volunteers who slept at inconsistent times developed insulin resistance and pre-diabetic symptoms after just ten days. Night-shift workers, eating when their organs expect fasting, suffer digestive disorders, obesity, and higher rates of type 2 diabetes. Even irregular bedtimes — so-called ‘social jet lag’ — harm cardiovascular health. Every hour of weekend catch-up sleep misaligns your body clock further, increasing your risks of heart disease and depression.

The Light Cure at Work

Yet, Geddes offers hope. In Sweden’s Forsmark Nuclear Power Station, engineers tested “circadian lighting” — lamps that mimic daylight’s shifting color. Workers beneath the reactors reported better alertness on night shifts and improved sleep afterward. NASA takes this idea further, equipping astronauts with tunable LEDs aboard the International Space Station, cycling through blue-white “daylight” and amber “pre-sleep” modes to simulate Earth’s day-night rhythm. The technology echoes nature’s forgotten cycles, restoring balance to humans trapped in artificial time zones.

The healing power of light, once dismissed as quackery, is now returning to modern science. Geddes revives the story of Dr. Niels Finsen, the 19th-century pioneer who used focused ultraviolet light to treat skin tuberculosis, earning the 1903 Nobel Prize. His success sparked a global “sun-cure” movement that linked sunlight to vitality and healing — from Swiss tuberculosis sanatoria to children’s rickets treatments. Today, Geddes argues, new research is rediscovering those truths in biochemical detail.

Sunlight and Immunity

Beyond vitamin D, the sun produces molecules that defend us in subtler ways. Ultraviolet rays trigger the release of nitric oxide — lowering blood pressure and protecting the heart — and modulate immune cells that prevent autoimmune attacks. In mice, low doses of UV light prevent multiple sclerosis-like diseases. Human studies hint the same is true: people living farther from the equator, or who conceal their skin, have higher rates of heart disease, MS, and depression. Vitamin D supplements alone can’t replicate sunlight’s broad spectrum of benefits.

A Double-Edged Cure

Of course, sunlight’s healing power comes with a warning. The same UV that promotes health also causes skin cancer, as demonstrated by scientist Margaret Kripke, who showed that excessive UV suppresses immune surveillance in mice, allowing tumors to grow. Still, Geddes highlights a paradox: outdoor workers, chronically exposed but rarely burned, develop more benign skin cancers yet live longer overall than indoor workers — whose sporadic sunburns raise melanoma risk but whose cardiovascular systems suffer from sun deprivation. The key is balance, not avoidance.

Addicted to Sunlight

Perhaps evolution explains why we seek the sun’s warmth instinctively. When sunlight touches your skin, it releases beta-endorphins — natural opioids that induce calm and pleasure. Geddes suggests this may underlie humanity’s universal love of sunbathing — and its dangers. The same pleasurable feedback can make tanning addictive, leading some to compulsively seek UV exposure much like drug users chase a high. Light, it seems, touches both our skin and our psyche.

When winter descends, many of us feel it in our bones. Geddes devotes a moving chapter to Seasonal Affective Disorder (SAD) — the recurring winter depression that afflicts millions, particularly in northern latitudes. Through patient stories and cutting-edge research, she frames SAD not as psychological weakness but as a physiological response to insufficient light.

How Darkness Alters the Brain

In the 1980s, psychiatrist Norman Rosenthal identified SAD after observing patients — including a data-obsessed engineer named Herb Kern — whose winter moods brightened with exposure to bright light. These individuals weren’t imagining their malaise: lower daylight reduces serotonin, the brain’s mood-regulating chemical, while prolonged melatonin secretion stretches biological night. Morning light therapy — 10,000 lux for 30 minutes — can reverse these changes in days. No pill acts faster.

The Power of Attitude and Culture

Yet, Geddes emphasizes, our mindset toward winter matters too. In Tromsø, Norway, where the sun vanishes for months, psychologist Kari Leibowitz found residents remarkably optimistic. Rather than battle winter, they embrace it with koselig — coziness, community, and outdoor activity. Their positivity protects them as much as artificial light does. Similarly, Scandinavian traditions of bright indoor spaces, saunas, and social connection act as psychological solar substitutes. By contrast, cultures that fear winter often experience deeper gloom.

The message is liberating: you can’t control the length of your days, but you can control how you meet them — by seeking brightness, both outside and within.

In one of the book’s most hopeful sections, Geddes explores how medicine is embracing chronotherapy — healing through timing. She visits Milan’s San Raffaele Hospital, where psychiatrist Francesco Benedetti treats severe depression using “triple chronotherapy”: deliberate sleep deprivation, timed bright light, and lithium. Counterintuitive but effective, the therapy resets patients’ circadian rhythms within days — often succeeding where drugs fail.

The Biological Basis of Healing Time

Chronotherapy extends beyond psychiatry. Geddes introduces Professor Francis Levi, who discovered that cancer patients tolerate chemotherapy better — and live longer — when drugs are administered in sync with their body clocks. Heart surgeries performed in the afternoon yield better survival rates than morning ones. Likewise, wounds heal faster if inflicted during daylight, when cell-repair enzymes are most active. The timing of sleep, meals, and even vaccines can drastically alter outcomes. Morning flu shots, for example, generate stronger immune protection than afternoon ones.

Bringing Light Back to Healing Spaces

Hospitals, however, often ignore natural rhythms. Geddes describes wards lit 24/7, their patients losing sense of time. Yet when Danish stroke units installed circadian lighting systems — bright by day, dim and warm by night — recovery times dropped and depression lessened. Alzheimer’s wards using similar systems saw calmer patients who ate and slept better. As Florence Nightingale once observed, “Nature alone cures.” Letting daylight in simply gives nature a chance to work.

In her concluding chapters, Geddes asks: what if society itself obeyed the sun? Visiting Bad Kissingen, Germany — the world’s first self-proclaimed “Chronocity” — she finds a town redesigning life around internal time rather than the clock. Schools delay start times to match teenagers’ delayed rhythms; offices offer flexible schedules; and public buildings are reoriented for daylight. The aim is social as well as biological well-being.

The Case Against Daylight Saving

Geddes critiques our twice-yearly clock changes, showing how “springing forward” costs lives: heart attacks and accidents spike in the days after Daylight Saving begins. Sleep debt and social jet lag ripple through society, lowering productivity and mood. Scholars like Till Roenneberg argue for abolishing DST altogether and aligning civil time more closely with solar time — a shift that would literally bring us back into sync with nature.

A New Enlightenment

Geddes ends where she began — beneath the sky. Humanity’s next revolution, she suggests, will be less about technology and more about returning to light itself: cultivating workplaces that honor natural rhythm, designing cities that channel sunlight rather than block it, and restoring the primal balance between light and dark. After millennia worshipping the sun, then centuries fleeing it, she calls for a reconciliation — one that lets us live, once again, in time with the turning Earth.