Laura: A 2007 study by the International Agency for Research on Cancer added something to its list of 'probable' human carcinogens. It wasn't a chemical or a new type of radiation. It was night-shift work. Sophia: Hold on. Just… working at night? Like, the job itself is a carcinogen? That sounds terrifying. I mean, I’ve pulled my share of all-nighters staring at a laptop. Does that count? Laura: That is precisely the kind of unsettling question at the heart of the book we're diving into today. It's Chasing the Sun: The New Science of Sunlight and How It Shapes Our Bodies and Minds by Linda Geddes. And she argues that yes, in a way, it does count. Sophia: Wow. Okay, so who is Linda Geddes to be making these huge claims? Laura: She's the perfect guide for this journey. Geddes is an award-winning British science journalist with a degree in cell biology. But what makes this book so compelling is that she's not just a theorist. For the book, she actually ran a personal experiment where she and her family tried to live without artificial light after 6 p.m. Sophia: She did what? With kids? That’s commitment. Okay, I'm listening. So before we get to the scary cancer stuff, what is actually going on inside our bodies? What is this 'clock' that my late-night Netflix binge is supposedly breaking?

Laura: It’s a beautiful and incredibly complex system. The simple version is that you don't just have one body clock. You have trillions. Nearly every single cell in your body, from your liver to your skin to your lungs, has its own tiny, molecular clock ticking away. Sophia: Trillions? That sounds like chaos. How does anything get done on time? Laura: That's where the master clock comes in. Deep in your brain, in the hypothalamus, there’s a tiny cluster of about 20,000 neurons called the suprachiasmatic nucleus, or SCN. Think of it as the conductor of a massive, body-wide orchestra. It sends out signals to make sure all those cellular clocks are playing in rhythm. Sophia: An orchestra conductor in my brain. I like that. So what’s the conductor’s baton? How does it know when to start the music? Laura: Light. Specifically, sunlight. Light hits the retina in your eyes and travels down a dedicated nerve pathway straight to the SCN. It’s the primary signal that tells your brain, "Okay, it's morning! Reset the clocks! Time to be awake and alert!" Without that daily reset, the whole orchestra starts to drift. Sophia: And what happens when it drifts? I mean, how bad can it be? Laura: It can be life-altering. Geddes tells the story of a man named Mark Galvin, who suffered from something called non-24-hour sleep-wake disorder. For most of us, our internal clock runs on a cycle that's roughly 24 hours long. His was longer. Sophia: What does that even mean in practice? Laura: It means that every day, his natural urge to sleep and wake shifted a little later. One week, he might be on a normal schedule. The next, he’d feel the need to go to bed at 4 a.m. and wake up at noon. The week after that, he’d be completely nocturnal. He couldn't hold a job. His relationships fell apart. He describes the constant disappointment on his girlfriend's face when he couldn't wake up for things. For years, people just told him he was lazy or undisciplined. Sophia: Oh, that's heartbreaking. To have your own biology betray you like that, and for no one to believe you. It must have been so isolating. Laura: Exactly. He said that finally getting a diagnosis at age thirty was a massive relief. A neurologist told him, "This is real," and for the first time, he felt validated. He wasn't mad, and he wasn't lazy. His clock was simply untethered from the 24-hour world because his brain wasn't getting or responding to that strong light signal needed for the daily reset. Sophia: So for the rest of us, that morning sunlight is literally the anchor that stops our bodies from just drifting off into jejich own timezone. Laura: It's the most powerful anchor we have. And that's where the modern world creates a massive problem. We've weakened that anchor and introduced a thousand false signals.

Sophia: Okay, so our bodies are these ancient, sun-powered machines. But we don't live in the ancient world. We live in Las Vegas, metaphorically speaking. That brings us to this idea of the 'Great Disruption,' right? Laura: Perfectly put. Geddes opens the book with this brilliant story of being at a conference in Las Vegas. She's in a windowless casino, under a ceiling painted to look like a sky, and she feels this desperate, primal need for real sunlight. But the entire city is designed to make you forget the sun exists. The goal is to keep you inside, spending money, unaware of whether it's 3 p.m. or 3 a.m. It's the ultimate symbol of our modern war on natural time. Sophia: It's a war we're all fighting, even if our living room isn't a casino floor. The book was praised for making this science accessible, but some readers felt it was a bit superficial. Does it offer a real counter-example? A control group for this crazy experiment we're all living in? Laura: It does, and it's fascinating. She looks at the Old Order Amish. They live in the modern world, but their rules limit their use of grid electricity. They spend their days working outdoors, getting four times as much bright light exposure as the average American. And at night? They use propane lamps, which are about a thousand times dimmer than a typical modern living room. Sophia: And what's the result? Laura: They go to bed earlier, sleep more soundly, and report far lower rates of the 'winter blues' or Seasonal Affective Disorder. Their melatonin levels rise and fall in perfect sync with the sun. They are a living testament to how our bodies are supposed to work. Sophia: But we can't all be Amish. We have jobs, we have screens. Is the book just saying we're all doomed? Laura: It's not about being doomed, it's about understanding the stakes. And for that, she gives a much more extreme example: US Navy submariners. For decades, they ran on an 18-hour 'day' to maximize efficiency. Six hours on watch, six hours for chores and food, six hours for sleep. Sophia: An 18-hour day? My brain hurts just thinking about that. Your body would never know what time it is. Laura: It was a disaster. The sailors were in a constant state of circadian chaos. Geddes tells the story of a commander, Seth Burton, who was routinely getting by on four hours of sleep a day in this high-stress, sunless environment. At age twenty-seven, he developed an aggressive cancer in his chest. He's convinced it was a direct result of the relentless schedule and profound sleep deprivation. Sophia: That is terrifying. And it shows that this isn't just about feeling a little groggy. This disruption has life-or-death consequences. Laura: Absolutely. The Navy eventually tested a 24-hour watch schedule and found the crew's reaction times were faster and their sleep quality dramatically improved. It proves that even in a submarine deep underwater, your ancient, 24-hour biology still rules. You can't just hack it with a new schedule. Sophia: This also explains what Geddes calls 'social jet lag,' doesn't it? The feeling you get on a Monday morning after staying up late and sleeping in all weekend. It's a mini-version of what those submariners went through. Laura: Exactly. Your body clock shifts a few hours over the weekend, and then on Monday, you force it back. For every hour of social jet lag, your risk of heart disease and obesity goes up. We're all giving ourselves a mild case of jet lag every single week.

Laura: And it's not just about avoiding the harm of disruption. The book argues we're actively missing out on the sun's benefits. We've become so afraid of it, but Geddes calls it 'Doctor Sunshine' for a reason. Sophia: Which feels so counterintuitive. My entire life, the message has been 'the sun is dangerous, it causes cancer, cover up.' Laura: And that risk is real. The book doesn't deny it. But it presents a fascinating paradox. A massive study in Sweden followed nearly 30,000 women for 20 years. It was called the Melanoma in Southern Sweden study. They wanted to understand melanoma risks. Sophia: Okay, and what did they find? I'm guessing the sun-worshippers had worse outcomes. Laura: The opposite. The women who actively sought out the sun—the sunbathers—had a longer life expectancy, by one to two years, than the women who actively avoided the sun. Sophia: Hold on. That can't be right. How? Weren't they getting more skin cancer? Laura: They were. They had a higher rate of melanoma. But here's the twist: their overall mortality rate was lower. They were far less likely to die from cardiovascular disease and other non-cancer illnesses. The study concluded that avoiding the sun was a risk factor for death on par with smoking. Sophia: That is a bombshell. It completely flips the script on public health messaging. So what is the sun doing for us that's so protective? Is it just vitamin D? Laura: That's part of it, and vitamin D is crucial for our immune system. The book links low vitamin D from lack of sun to higher rates of things like Multiple Sclerosis, especially in countries farther from the equator. But Geddes argues it's more than that. Popping a vitamin D pill isn't the same as getting sunlight. Sophia: Why not? Laura: Because sunlight does other things. For instance, when UV light hits our skin, it triggers the release of nitric oxide into our bloodstream. Nitric oxide is a powerful vasodilator, meaning it relaxes our blood vessels and lowers blood pressure. This might be a huge reason why sun exposure is linked to better heart health. Sophia: So the sun is literally helping our hearts relax. Laura: And it’s making us happier. Sunlight on the skin also triggers the release of ß-endorphin, the body's natural opiate. It’s a feel-good chemical. That's not just a poetic idea; it's a biological reality. It's why being in the sun feels so good. It’s a genuine, chemical-driven pleasure response. Sophia: This is blowing my mind. We've been so focused on the one major risk—skin cancer—that we've ignored this whole portfolio of benefits for our heart, our immune system, and our mood. Laura: Precisely. The book's argument is that we need a more nuanced relationship with the sun. It's not about choosing between being a sun-avoider or a reckless tanner. It's about finding a healthy, respectful balance. It's a double-edged sword, and we need to learn how to handle it wisely.

Sophia: So where does this leave us? It feels like we're caught in this impossible bind between our ancient biology, which craves the sun, and our modern reality, which is all about screens, offices, and fear of UV rays. What's the big takeaway here? Laura: I think the core message is that our relationship with light is a biological necessity, not a lifestyle choice. For the last century, we've treated sunlight as optional—something to be managed, avoided, or replaced with an artificial substitute. But the evidence Geddes presents shows that the consequences of that severance are written all over our health statistics. Sophia: It’s a contract we broke without realizing it. Laura: Exactly. The book isn't a prescription to abandon modern life and live in a field. It's a powerful plea to remember that we are, fundamentally, animals who evolved on a rotating planet. Our health depends on honoring that rhythm. We need the bright, brilliant light of day, and we need the true, profound dark of night. Sophia: So it’s about reintroducing those extremes back into our lives. Laura: Yes. And it doesn't have to be radical. Maybe the first practical step, the one thing anyone can do, is just to get 10 or 15 minutes of direct sunlight first thing in the morning. No sunglasses. Just let that bright, natural light hit your eyes and tell your brain's conductor, "It's time to start the day." Sophia: That feels manageable. And maybe it makes you ask a bigger question, too. When was the last time you were somewhere so dark you could actually see the Milky Way? When was the last time you really experienced true darkness? Laura: A perfect question to end on. It's about rediscovering both sides of that coin. We'd love to hear from our listeners about this. What's your relationship with sunlight and darkness? Have you noticed how it affects your mood or your sleep? Find us on our social channels and share your story. Sophia: It’s a conversation we all need to be having. Laura: This is Aibrary, signing off.