You wake up and the light is different. Not just dimmer, but a sort of bruised gold color that wasn't there last week. Your nose is slightly stuffed, your joints feel like they need a hit of WD-40, and you’re suddenly exhausted by 4:00 PM. It isn’t just in your head. The changing of the seasons is a massive physiological event that triggers everything from your endocrine system to your gut microbiome. Most people think it’s just about swapping sweaters for T-shirts, but it’s actually a violent recalibration of your internal clock.
Honestly, the planet is shifting, and you’re just along for the ride.
The Earth’s axial tilt—that 23.5-degree lean—is the culprit here. As we orbit the sun, the angle of light hitting your specific patch of dirt changes. This isn't just "weather." It's a fundamental shift in the amount of UV radiation and photoperiod (day length) your eyes perceive. Your retina sends this data straight to the suprachiasmatic nucleus in your brain. That’s your master clock. When it gets confused by the changing of the seasons, your whole system goes into a bit of a tailspin.
The Biological Reality of the Changing of the Seasons
We talk about "Spring Fever" or "Autumn Blues" like they’re poetic metaphors. They aren't. They are chemical reactions.
Take Vitamin D, for example. In the Northern Hemisphere, between October and March, the sun literally doesn’t get high enough in the sky for your skin to produce Vitamin D3 if you live above a certain latitude (roughly 37 degrees north). That’s the "Vitamin D Winter." When your levels crater during the changing of the seasons, your serotonin drops too. Serotonin isn't just for mood; it helps regulate your appetite and sleep. This is why you suddenly want to eat an entire loaf of sourdough bread when the leaves start to turn. Your body is screaming for a quick glucose hit to compensate for the lack of "sunny" neurochemistry.
Then there's melatonin. This hormone is light-sensitive. As days shorten, your body starts producing it earlier in the evening. You feel sluggish. You feel like a human version of a computer running too many background apps. Conversely, when spring hits, the sudden surge in light suppresses melatonin and spikes cortisol. It’s a shock. You might find yourself staring at the ceiling at 3:00 AM, wondering why your brain won't shut up.
It's in your blood—literally
Research from the University of Cambridge in 2015 actually found that our very genes change with the seasons. They analyzed the blood and fat tissue of over 16,000 people and found that thousands of genes—about a quarter of the entire genome—showed seasonal variation. In the winter, your immune system goes into a pro-inflammatory state. It's preparing to fight off the flu and other respiratory nasties. In the summer, your body shifts its genetic expression toward heat regulation and tissue repair.
This isn't a "soft" change. It's a hard-coded biological survival mechanism.
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Why "Fall Back" and "Spring Forward" Still Ruins Everything
We can't talk about the changing of the seasons without mentioning the nightmare that is Daylight Saving Time (DST). While the physical tilt of the Earth moves gradually, our clocks move abruptly. It’s a self-inflicted wound.
The American Academy of Sleep Medicine has been shouting into the void for years about how the spring transition increases the risk of heart attacks by about 24% on the Monday following the switch. Why? Because the sudden loss of an hour of sleep, combined with the seasonal shift in light, creates a massive spike in systemic stress. Your heart basically says, "I wasn't ready for this."
Even without the clock change, the atmospheric pressure shifts that accompany the changing of the seasons are brutal on people with migraines or arthritis. When a cold front moves in, barometric pressure drops. This allows tissues in your body to expand slightly—not enough to see, but enough to put pressure on your nerves and joints. If you've ever heard an older relative say they can "feel the rain coming in their bones," they aren't kidding. They are living barometers.
The Seasonal Affective Disorder (SAD) Misconception
Most people think SAD is just feeling a bit "meh" in December. But it’s a clinical subtype of major depression. And here’s the kicker: it’s not just a winter thing. There is such a thing as Summer SAD.
While Winter SAD is linked to a lack of light and a surplus of melatonin, Summer SAD is often triggered by too much heat and humidity. Some researchers believe it's a "heat intolerance" issue. Instead of the lethargy and overeating seen in winter, summer sufferers often deal with agitation, insomnia, and poor appetite. It’s the flip side of the same seasonal coin.
The changing of the seasons acts as a trigger for these vulnerabilities. If your circadian rhythm is brittle, these transitions break it. This is why light therapy is so effective for some—it’s not about "fake sun," it’s about providing a clear, high-contrast signal to the brain so it knows exactly what time it is.
Micro-seasons and the 72-season calendar
In Japan, there is a traditional calendar that divides the year into 72 micro-seasons, each lasting about five days. This reflects a much deeper understanding of the changing of the seasons than our blunt "four seasons" model. It recognizes things like "The first frogs start to croak" or "The wind blows the hibiscus flowers."
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When we only acknowledge four big blocks of time, we miss the subtlety of the transition. We expect ourselves to be the same person on September 1st as we were on August 31st. We aren't. The humidity dropped 20%, the dew point shifted, and your body is trying to figure out how to conserve water differently.
How Your Microbiome Joins the Party
This is the part that usually surprises people. Your gut bacteria actually change during the changing of the seasons.
A study of the Hadza hunter-gatherers in Tanzania showed that their gut biomes shifted dramatically between the wet and dry seasons. While modern humans have air conditioning and grocery stores, our guts still hold onto some of that ancient programming. In the winter, we tend to eat more fat and preserved foods. In the summer, we lean toward fresh fiber.
Your microbes are like a tiny, invisible garden. When the "climate" of your body changes—due to temperature shifts or different seasonal foods—the species that thrive in your gut change too. If you’re feeling bloated or "off" during a seasonal transition, it might just be your microbiome going through a hostile takeover.
What Most People Get Wrong About Seasonal Wardrobes
We think of clothes as "fashion," but they are actually external thermoregulation. During the changing of the seasons, the biggest mistake people make is ignoring their extremities.
Your body prioritizes keeping your core warm. When the temperature drops, it pulls blood away from your hands and feet (vasoconstriction). If you’re walking around in a heavy coat but wearing thin socks and no hat, your body is working twice as hard to maintain its equilibrium. This causes fatigue. You’re literally burning calories just trying to keep your blood moving correctly.
Pro tip: In the transition months, focus on your neck and ankles. These are high-heat-loss areas where blood vessels are close to the surface. Keeping them covered tells your nervous system that everything is okay and it doesn't need to go into "survival mode."
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Navigating the Shift: Practical Survival Steps
Stop fighting the changing of the seasons and start leaning into the biological reality. You can't out-hustle the Earth's orbit.
Prioritize Light Hygiene
In the autumn and winter, get outside within 30 minutes of waking up. Even if it’s cloudy. The lux (light intensity) outside is still significantly higher than your indoor LED bulbs. This resets your clock. In the spring and summer, wear sunglasses in the afternoon to signal to your brain that the day is actually ending, even if the sun is still up at 8:00 PM.
Adjust Your Internal Thermostat
Stop keeping your house at a constant 72 degrees year-round. It’s making you "thermally brittle." Letting your environment fluctuate a bit—cooler in the winter, warmer in the summer—helps your body maintain its ability to adapt. This is called "metabolic flexibility."
Eat for the Light, Not the Calendar
If the sun is setting early, eat your heaviest meal earlier. Your body's ability to process glucose drops after dark. During the changing of the seasons, your insulin sensitivity follows the light. Eating a big bowl of pasta at 9:00 PM in the winter is much harder on your system than doing it in July.
The "Two-Week Grace Period"
Give yourself a buffer. Every time the season shifts, acknowledge that your cognitive performance might dip for about 14 days. You’ll be more forgetful. You’ll be tired. You’ll probably be a bit cranky. That’s not a character flaw; it’s a systemic reboot.
Actionable Insights for the Current Shift:
- Check your labs: If you feel "seasonal" fatigue, get your Vitamin D and Ferritin (iron) levels checked. Don't just guess.
- Morning Sunlight: Use a 10,000 lux light box if you can't get outside in the winter. 20 minutes is the sweet spot.
- Temperature Exposure: Try contrast showers (hot/cold) to help your blood vessels regain the elasticity they need for seasonal temperature swings.
- Hydration Shift: You need more electrolytes in the winter than you think. Indoor heating is incredibly dehydrating, often more so than summer sweat.
The changing of the seasons is the most consistent thing in our lives, yet we’re surprised by it every single year. Stop trying to be a static being in a dynamic world. Your body is a biological machine that responds to the tilt of the planet. Let it do its job. Turn the lights down, put on the wool socks, and stop wondering why you're tired. You’re just being a human.