How Our Bodies Adapt to Early Fall: Light, minerals & the physiology of seasonal change

A Rewilded Wellness approach to seasonal health

What happens during a seasonal transition, and how our relationship with our foundations can change as we become more capable of responding to our bodies.

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We crossed the fall equinox on September 22, the start of Libra season and the real turn into autumn. The equinox is the moment light and dark come into balance, and they don't stay there. The days keep getting shorter from that point on, which is a good picture of what balance looks like in a living system. It moves.

We're at the very beginning of fall. When most of us think about fall, we jump ahead to Halloween, Thanksgiving, the clocks changing, and cold and flu season. Those belong to later phases. Right now the season is still establishing itself, and many of us are adjusting to it without having named what we're adjusting to.

I noticed it this year because the weather turned on me fast. The temperature dropped hard right around the equinox, and I felt myself tighten in response, less loose, less fluid, more contracted than I'd felt even a week earlier. I can't tell you what was happening in my tissue. I can tell you that I noticed the change almost exactly when the season changed, and that noticing is the point of this piece.

Ayurveda has a concept called ritusandhi, the junction between seasons, which John Douillard often teaches. It gives special attention to the seven days before a seasonal change and the seven days after. I find that framing useful because it names something I recognize, which is that the handoff between seasons deserves attention as much as the seasons themselves. Fall has phases, the way any season does, and the middle of fall and the run into winter will ask different things of us than these first weeks do. So what is changing this early in fall, and what do you need to know about this stretch of the year?

Libra season, and the doorway it opens

One way into that question is through Libra, the sign we just entered. Libra is symbolized by the scales, which fits a season that opens right at the point where light and dark come into balance. In traditional medical astrology, Libra is also associated with the kidneys and the lower back.

Whether or not you use astrology as a health framework, I find that pairing worth paying attention to, because the kidneys are one of the clearest examples we have of what balance looks like in the body. They don't hold one steady setting. All day long they adjust how much water you keep, how much sodium you hold onto, and how much pressure your system runs at, based on what's happening to you at that moment. That's the idea I want to follow through the rest of this piece: balance is responsive, not static. So let's start with the kidneys and what they're responding to now.

What's shifting in your fluid and mineral physiology

July and October place different fluid and electrolyte demands on your body. Hot weather, heavy sweating, and higher activity create one set of losses and one set of regulatory responses. Cooler weather, less sweating, and different thirst, activity, and vascular conditions create another. Your kidneys keep regulating sodium, potassium, and water according to what's happening around you, using hormones like aldosterone and vasopressin to make those adjustments in real time.

Blood pressure shifts with the season as well. In large clinic datasets the average swing between summer and winter is modest, roughly a point or two of systolic pressure, and it tends to be larger in some groups, such as older adults with high blood pressure. Cold-induced vasoconstriction is one contributor. As your blood vessels narrow in response to cold, resistance rises and your heart works against more pressure. It isn't the whole explanation, but it is a well-documented piece of it.

Most of us don't think of fluid and mineral needs as something that changes with context, and the marketing for electrolyte products often doesn't help. It's the same packet and the same ratio in every season, as if your relationship to salt and water were a constant you correct once and maintain forever. Why would we turn electrolytes into a static rule when electrolyte balance itself is dynamic?

My own practice is a good example of that. I lean on my electrolyte drink mostly in summer, and I reach for it at other times of year when it fits, not on a fixed schedule. The rest of the year, minerals and hydration show up throughout my day in other ways: mineral-containing water, herbal infusions, broth, and food that's salted well. It took time to get here. When I first started paying close attention to my hydration and mineral status, I needed more structure, more deliberate tracking, and more conscious effort to build the habit at all. Over the years, as I gained experience and capacity, much of that structure became part of how I already eat and live, so I don't have to manage it the way I once did.

[mention my mineral foundation mini course here]

That doesn't mean the original structure was wrong, and it doesn't mean anyone should drop a practice the moment it starts working. My electrolyte recipe can still be a useful starting structure for someone. A foundation doesn't have to stay a permanent rigid rule just because it was useful during one phase. Rewilding isn't about trading structure for intuition. It's about letting knowledge, observation, and lived experience start working together, so something that began as a deliberate practice can become part of a more responsive relationship with your body.

None of this lands the same way on everyone, because our exposures differ. Air conditioning changes how much summer heat you encounter, and heating changes how much cold you experience. How much time you spend outside, how active you are, how much you sweat, and what you eat and drink all change the conditions your body is responding to. Season matters, and so does the life you're living inside that season.

Light gives us another example

Light is the main timer your nervous system uses to know what time of day, and what time of year, it is. Your eyes take in the changing quality and duration of daylight and use it to set your internal clock. That clock does more than govern when you feel alert or sleepy. It organizes a cascade underneath that, including the timing of your cortisol and melatonin rhythms, your appetite and meal timing, and how your body handles glucose across the day. Light is one of the main inputs your body uses to organize its physiology across each 24-hour cycle, and that input is changing every day as the days get shorter.

Here's where it gets complicated. Most of us aren't living inside the natural light environment that shaped this system. Our bodies can only respond to the light information they receive, and indoor lighting is a tiny fraction of the brightness of daylight, even on a gray day outside. If you wake up under artificial light, commute in a car, and work indoors under fluorescents or LEDs, your circadian system is getting a muted version of the signal that's shifting outside.

Why we stopped noticing

Most of us have stopped noticing the season because our lives are built to make that easy. Our houses stay the same temperature in July and January, and our evenings stay bright long after the sun goes down. You can buy a tomato any month of the year, even though tomatoes peak from late summer into early fall, and the one you find in January isn't the same tomato you'd pull off the vine in September. I'm grateful for a lot of that comfort. It does mean the cues that used to announce the time of year, the heat, the cold, the length of the day, and the food in front of us, reach us in a much quieter form.

My garden makes the season easy to see, because it has no way of ignoring it. Right now I'm pulling storage crops out of the ground, roots and tubers built to carry through the dark months instead of being eaten fresh this week. The plants around them are doing something different than they were doing in June. Some are dying back, some are setting seed, and all of them are responding to the shortening light. Nobody in the garden is debating whether the season has changed. Food is shifting right now too, and I'm saving that conversation for another episode, but the garden already shows the larger picture: the season keeps moving whether or not we're outside to see it.

What to do with all of this

I don't want to leave this as an interesting conversation about seasonal physiology, because the whole point is learning how to notice these shifts in your own life. Light and fluids give us two simple places to practice. Sun, sleep, hydration, minerals, and movement matter in every season, and none of them needs replacing. What changes is the environment we're practicing them in.

Start with light. Over the next week or two, pay attention to how much daylight reaches you and when. Notice when the sun is coming up compared with a month ago, and whether you're outside for any of it. Try getting outside in the morning and again later in the day, and watch what happens to your energy, your sleepiness in the evening, and your appetite. Bright light in the evening, from screens and overhead lights long after dark, is also a signal your body responds to, so it's worth looking at what your evenings are like now that the dark comes earlier.

Then look at your fluids. In August you were probably sweating more, and whatever you were doing for hydration and minerals was sized for that. Now it's cooler and you may be sweating a lot less, so ask whether what you're drinking still fits the day you're having. If you use an electrolyte product every day, ask whether the conditions that made it useful in August are still there. Some days they are, if you're training hard, sweating, or sick, and some days they aren't. Watch what your thirst, your energy, and your sweating are doing, and adjust from there. If a doctor has told you to limit fluids or sodium, or you take blood pressure medication, keep following that guidance and bring these questions into that conversation.

Every seasonal transition is also a natural time to take stock, the way I do in the garden this time of year. I'm noticing what grew well and what didn't, what's worth storing, what has finished its cycle, and what I want to carry forward. I don't think our bodies go through a prescribed autumn detox. The conditions around us have changed, and that makes this a useful time to ask what still fits.

Balance isn't a setting we reach. It's something our bodies are continually negotiating, and the more we practice noticing what they're responding to, the better we get at adjusting along with them.

Season shows up in lab work too. Some studies have found that markers like fasting glucose, insulin, and thyroid hormones vary with the time of year, though the results differ between studies, and even without that, a lab result is a snapshot of one body under one set of conditions. That's why I don't treat testing as an answer by itself.

Testing gives you information, and the work is learning what it means in the context of your body, your history, and what we learn as we watch your patterns over time. If you've been collecting health information for a while, testing, supplements, recommendations from a dozen directions, and you still don't know what matters for you right now, that's the gap this work is for. I currently have four October openings for Minerals & Microbes if you're ready to do that work with me directly.