The Science of Seasonal Affective Disorder: How Heat + Cold Contrast Therapy Regulates Your Circadian Rhythm

You've noticed it, haven't you?

The sun's setting before dinner now. An unexplained heaviness settles in around 3pm. You're hitting snooze more often, and your morning coffee isn't cutting through the fog like it used to. Maybe you chalked it up to summer being over, back-to-school chaos, or just "getting older."

Here's what's actually happening: October is when your circadian rhythm—your body's internal 24-hour clock—begins its seasonal disruption. And this isn't "just in your head." This is measurable and biological… and it's happening in your brain right now.

The good news? While most people wait until they're deep in the winter blues to take action, science shows us that October is actually the perfect time for intervention.

And one of the most effective tools isn't a pill or a therapy session—it's an ancient practice modern research is finally understanding:

Contrast Therapy, or using heat and cold.

Let's talk about what's really going on in your body this fall, and what you can do about it.

What Seasonal Affective Disorder is Doing to Your Body in October

Your circadian rhythm is controlled by a cluster of neurons in your brain called the suprachiasmatic nuclei (SCN). These neurons are remarkably sensitive to light and act as your body’s master clock, coordinating everything from when you feel sleepy to how your immune system functions.

Here's the problem: as daylight hours shrink in October, that earlier sunset doesn't just mean less time at the park with your kids. It's triggering a biological cascade that affects your hormones, your mood, and your energy levels.

The science is clear. Studies published in major journals like PNAS and Nature Translational Psychiatry have documented this phenomenon extensively. When fall arrives at temperate latitudes like Northern California, something called a "phase delay" occurs. Your body's internal clock starts to lag behind your actual sleep-wake schedule. It's like permanent jet lag, except you never left town.

This delay triggers a domino effect:

Melatonin (your sleep hormone) starts being produced earlier in the day, making you feel sluggish when you should feel alert. 

Serotonin levels drop as its metabolic relationship with melatonin shifts. 

Cortisol timing gets thrown off, disrupting your stress response and energy patterns throughout the day.

The result? Depression, anxiety, difficulty concentrating, and that frustrating feeling of "non-restorative sleep"—where you sleep 8 hours but wake up exhausted. This affects an estimated 10 to 20% of people in regions like ours, with women being particularly susceptible.

Here's what most people don't realize: Seasonal Affective Disorder doesn't start in January when you're buried under gray skies. It begins now, in the fall, when your body first loses its rhythm. By the time winter hits, you're months into dysregulation.

The good news? October is the perfect time to get ahead of the ‘sadsies’ and get your rhythm back! 

The Cold Plunge Effect: Your Biological Reset to Regulate Your Rhythm

This is where the science gets really interesting.

When researchers immerse people in cold water—around 57°F (14°C)—something remarkable happens almost immediately. The body releases a massive surge of neurotransmitters, including norepinephrine and dopamine. We're not talking about modest increases. Studies document a 530% increase in norepinephrine and a 250% increase in dopamine during cold water immersion.

To put that in perspective, many antidepressant medications work by increasing norepinephrine levels. You're getting a similar biochemical effect, but through a natural mechanism that your body has been designed to respond to for thousands of years.

But here's what makes this particularly relevant for seasonal circadian disruption:

Norepinephrine is your brain's natural wake-up call. It increases arousal, cognitive function, energy, and focus. When your circadian rhythm is delayed—when your body thinks it's time to sleep but your life says it's time to work—norepinephrine acts as a powerful corrective signal. It's directly involved in regulating your sleep-wake cycle, and low levels are linked to depression.

Dopamine enhances your goal-directed behavior, mood, motivation, and focus. Unlike the quick spike you get from social media or sugar (followed by a crash), cold-induced dopamine elevation lasts for 5 to 6 sustained hours. This is your body giving you natural, crash-free energy.

But the circadian benefits go even deeper. Recent fMRI studies (brain imaging) show that cold water immersion actually increases neural communication between large-scale brain networks—particularly in areas involving emotion regulation and self-control like the medial prefrontal cortex and anterior insula. People in these studies consistently reported feeling more active, alert, attentive, inspired, and less distressed after cold exposure.

Think of morning cold plunging as sending your body an undeniable signal: "It's time to be awake. It's time to be alert. It's time to engage with the day." When your circadian rhythm is trying to delay your wake time, cold immersion acts as a biological override, helping to correct that phase delay.

The optimal protocol based on research? Water temperature between 50 and 59°F, for 1 to 5 minutes, with morning exposure being most beneficial for those dealing with delayed circadian phase (which is most people with fall-onset mood changes).

The Complete Fire & Ice Cycle: Why Alternating Heat and Cold Is Even More Powerful

If cold water alone sends a wake-up signal, the complete Fire & Ice experience—alternating between heat and cold—creates something even more profound for your circadian health.

Here's the magic: One of the key signals your body uses to know it's time to sleep is a drop in core body temperature. This cooling triggers melatonin production in your brain. But in our modern world—with artificial light, temperature-controlled homes, and screen time before bed—this natural temperature curve often gets flattened or disrupted.

Capitol Floats' Fire & Ice rooms change that equation entirely.

Our contrast therapy rooms feature a steam sauna paired with cold plunge, designed for you to alternate between the two in a complete 45-minute cycle—the optimal appointment length for full circadian support.

How the Alternating Cycle Works

When you move between steam heat and cold immersion, you're not just raising and lowering your temperature. You're creating a vascular workout that amplifies all the benefits we've discussed.

The steam sauna phase intentionally raises your core body temperature while the humid heat opens your airways and deeply relaxes your muscles. Blood vessels dilate, circulation increases, and your body enters a state of profound relaxation. The heat triggers the production of heat shock proteins (HSPs)—specialized molecules that assist in cellular repair and protect against oxidative stress. Think of these as your body's maintenance crew, working to enhance recovery and build resilience.

The cold plunge phase then causes vasoconstriction—blood vessels tighten, blood shunts to your core, and that massive neurotransmitter release we discussed earlier floods your system.

The alternation itself—moving between these extremes 2-3 times within your 45-minute session—creates what researchers call a "pumping effect" in your circulatory system. Your blood vessels are essentially doing calisthenics, expanding and contracting, which enhances circulation far beyond what either temperature alone could achieve.

The Circadian Benefits of the Complete Cycle

This alternating pattern is particularly powerful for circadian regulation because it gives your body clear, unmistakable signals.

When practiced in the evening (1 to 3 hours before bed), the final cooling phase after your last round creates that pronounced temperature decline your body recognizes as bedtime preparation. Research shows this cooling mimics and enhances your natural sleep preparation process.

Studies on sauna use and sleep quality consistently find that people fall asleep more easily and experience deeper, more restorative slow-wave sleep after incorporating contrast therapy into their routine. One study published in Chronobiology International specifically examined the connection between sauna bathing and melatonin production, finding that the practice helps modulate the release of this crucial sleep hormone.

The steam sauna activates your parasympathetic nervous system (your "rest and digest" mode) and lowers cortisol levels. Cortisol is your stress hormone, and when it remains elevated in the evening, it directly suppresses your immune function and disrupts sleep. The combination of humid heat, the meditative quality of moving between temperatures, and the deep physical relaxation provides one of the most effective natural ways to down-regulate a stressed system.

Research from Finland—where sauna bathing is woven into the culture—has documented profound long-term benefits. Regular sauna use is associated with reduced cardiovascular disease risk, lower all-cause mortality, and even decreased risk of neurodegenerative diseases like dementia. The cardiovascular effects alone (increased heart rate, improved circulation, enhanced blood flow to the brain) support the kind of mental clarity that's often the first casualty of circadian disruption.

The 45-Minute Protocol

Capitol Floats' Fire & Ice sessions are designed as 45-minute appointments—the perfect length for 2-3 complete rounds of alternating heat and cold. This isn't arbitrary; it's the duration that allows your body to fully experience the benefits of contrast therapy while fitting into a realistic schedule.

A typical session might look like:

• Steam sauna: 10-15 minutes

• Cold plunge: 1-3 minutes (start slowly and build up your tolerance)

• Rest/transition: 2-3 minutes

• Repeat for 2-3 rounds

  
  

Morning Protocol (For Energy, Alertness, and Phase Correction)

Start with a gentle sauna warm-up—around 10 minutes. This prepares your body and isn't the main event.

Move to the cold plunge for 2 to 3 minutes. If you're new to cold exposure, start with 30 seconds and build from there. The goal isn't suffering; it's adaptation. Focus on your breath and staying calm. Research actually shows that the more you’re able to relax into the cold, the better your results. Think calm, slow breathing, relaxed muscles and soft face. This is where the magic happens.

Repeat 2-3 times and always end on cold for that alertness boost.

Frequency: 2 to 3 times per week.

What you're accomplishing: You're training your nervous system to wake up on command. You're flooding your brain with the exact neurotransmitters that counteract delayed circadian phase. You're telling your body, in the most primal language it understands, that it's time to be active and engaged.

Evening Protocol (For Sleep Quality and Relaxation)

This one's sauna-focused. Spend 15 to 20 minutes in the warmth, allowing your muscles to fully relax and your core temperature to rise.

Follow with a brief cold plunge—just 1 to 2 minutes. This isn't about intensity; it's about the contrast. The goal is the cooling phase that happens afterward. Always end on cold. 

Do this 1 to 4 hours before you want to be asleep.

Frequency: 2 to 4 times per week.

What you're accomplishing: You're creating that clear temperature signal your body needs to prepare for sleep. You're lowering stress hormones. You're activating your parasympathetic nervous system. You're essentially giving your circadian rhythm a roadmap when seasonal changes have made the path unclear.

Amplify with Float Therapy

Consider adding a float session 24 to 48 hours after your Fire & Ice practice. The 1,100+ pounds of magnesium sulfate in our float tanks supports stress reduction and sleep quality, while the sensory deprivation allows your nervous system complete rest. It's integration time for everything your Fire & Ice practice initiated.

What to Expect

Immediately: You'll notice the mood shift and energy change. Most people walk out of their first session surprised by how alert yet calm they feel.

Week 1-2: Better sleep onset, easier morning wake-ups, more stable afternoon energy.

Week 3-4: The circadian rhythm starts stabilizing. You'll notice you're more resilient to those darker evenings. Your mood feels more even.

Ongoing: By consistently practicing through October and into winter, you're building resilience to the seasonal changes rather than just reacting to them once they've already taken hold.

Your Body Is Speaking—Are You Listening?

Here's what we want you to understand: Your circadian system is sophisticated. It evolved over millions of years to help you adapt to changing seasons. But it evolved in a world where humans were much more exposed to temperature extremes, where wake and sleep times aligned more closely with light availability, where artificial light didn't convince our brains it was noon at 10pm.

Contrast therapy—alternating heat and cold exposure—isn't a "biohack" or a wellness trend. It's a way of speaking to your biology in its native language. It's providing the signals your body would have naturally encountered before our modern, temperature-controlled, artificially-lit world flattened out those experiences.

The science backing this isn't fringe. These are peer-reviewed studies published in journals like PNAS, Nature, and BMC Biology. This is research from institutions like Stanford, Harvard, and universities across Finland (where they've been studying sauna therapy for decades).

At Capitol Floats, our job is simple: we create the environment where your body can remember what it already knows how to do. We provide the tools—the precisely controlled temperature, the privacy, the guidance, the time.

All you have to do? Try something that might feel unfamiliar at first, but that humans have been doing for thousands of years.

We'll be here when you're ready.

Book your Fire & Ice session at Capitol Floats! First-time? Our staff will walk you through everything. You've got this.

Seasoned pro and ready to full send? Explore our Unlimited Fire & Ice Membership

Pro tip: Combine your Fire & Ice practice with morning outdoor light exposure (even 10 minutes helps) and a consistent sleep schedule. Your circadian rhythm responds to multiple inputs, and the more aligned signals you provide, the faster it recalibrates.