It’s 4:47 PM and it’s already dark outside. You’re sitting at your desk, staring at your screen, and you realize you haven’t stepped outside since this morning. There’s a heaviness in your chest you can’t quite name. It’s not depression, exactly. Just… less. Less energy. Less motivation. Less you.

If this sounds familiar, you’re not alone. And more importantly — you’re not imagining it.

Here’s What I See All the Time

When the days get shorter, something shifts in your body that most people never connect to the calendar. You wake up in the dark, work through the daylight hours indoors, and by the time you’re done, it’s dark again. Your body starts to feel it before your mind catches up.

The sluggishness. The brain fog. The way coffee stops working around 2 PM.

You tell yourself you’re just tired, or stressed, or getting older. Maybe you need to optimize your schedule better. Maybe you’re not disciplined enough. So you try the usual fixes — more coffee, earlier bedtimes, pushing through the fatigue — but nothing quite lands.

The tiredness lingers. The mental fog stays. And slowly, without realizing it, you start to accept this dimmed-down version of yourself as normal for this time of year.

But here’s what most people don’t see: the cost isn’t just productivity. It’s the way you show up at home. The patience you don’t have with your kids. The evening workout you skip because you’re too drained. The weekend plans you cancel because leaving the house feels like too much effort.

You’re functioning, but you’re not thriving. And somewhere deep down, you know this isn’t how it’s supposed to feel.

Let Me Share What’s Actually Happening

Your body needs sunlight to produce Vitamin D. Not just for bone health — that’s what most people think — but for something much more immediate: Vitamin D plays a direct role in regulating serotonin, the neurotransmitter that helps you feel balanced, focused, and like yourself.

When sunlight disappears for months at a time, your Vitamin D levels drop. And when that happens, your mood, energy, and mental clarity follow.

This isn’t about being weak or needing to push harder. It’s physiology. Your brain is running on less of what it needs to function well.

Here’s the thing most people don’t realize: the decline is gradual. You don’t wake up one day with a Vitamin D deficiency — it creeps in over weeks. By November or December, your levels may have dropped 30-40% from where they were in August, but because it happens slowly, you attribute the symptoms to stress, aging, or just “the season.” You never think to check whether your body is literally running on less fuel than it needs.

For high-performers, this is particularly challenging because you’re used to solving problems with strategy and discipline. But no amount of willpower can compensate for a biochemical deficiency. You can’t think your way out of low Vitamin D the same way you can’t think your way out of dehydration.

💡 Performance Insight: Studies show that up to 42% of U.S. adults are Vitamin D deficient, with rates climbing even higher during winter months and among people who work indoors. Research published in the Journal of Clinical Endocrinology & Metabolism found that adequate Vitamin D levels are associated with improved mood, cognitive function, and sleep quality.

Your brain needs the raw materials to produce the neurotransmitters that regulate mood, focus, and energy. When those raw materials are missing, everything gets harder.

A Moment from the Coaching Room

I had a client — let’s call him David — who came to me in January completely convinced he was burned out. He was an executive at a tech company, running on fumes, struggling to make decisions, dreading mornings.

We went through his schedule. His sleep. His workload. Everything looked manageable on paper. No red flags. No obvious stressors beyond the normal executive load.

Then I asked: “When’s the last time you had bloodwork done?”

He paused. “Uh… maybe two years ago? For my annual physical?”

I suggested he get a full panel, including Vitamin D. Two weeks later, he texted me a screenshot of his lab results. His Vitamin D was 22 ng/mL — technically not “deficient” by clinical standards, but well below the optimal range of 40-60 ng/mL that most functional medicine practitioners recommend for mood and energy.

We added a supplement (Vitamin D3 with K2, 5,000 IU daily), and I encouraged him to get outside for 10 minutes every morning, even if it was cloudy.

Within three weeks, he texted me: “I feel like myself again. I didn’t realize how much I’d been running on empty.”

It wasn’t burnout. It was biology.

⭐ Client Spotlight: Another client, Sarah, had been struggling with afternoon energy crashes and low mood every winter for years. After optimizing her Vitamin D levels and adding a morning light therapy routine, she reported: “I used to dread winter. Now I actually have energy in the afternoons, and I’m not fighting the urge to hibernate by 6 PM.”

Real Talk: What You Can Actually Do About This

Let’s be honest — you don’t need another overwhelming list of things to do. You need a few small, realistic actions you can take starting today. Here are the ones that actually move the needle:

Morning sunlight walk — Even 10 minutes outside before 9 AM helps your body regulate its internal clock and boosts natural Vitamin D production. Your skin is most efficient at producing Vitamin D when the sun is at a higher angle, and morning light also helps reset your circadian rhythm, which improves sleep quality. Cloudy day? Still counts. UVB rays penetrate clouds, and the exposure to natural light signals your brain to wake up. You’re not looking for perfection here — just consistent exposure.

Eat Vitamin D-rich foods — Salmon, mackerel, sardines, egg yolks, fortified dairy, and mushrooms that have been exposed to UV light are all solid sources. A 3-ounce serving of wild-caught salmon provides about 570 IU of Vitamin D. These won’t replace the sun entirely, especially in winter, but they help fill the gap and provide other nutrients that support overall health. If you’re meal prepping on Sundays, this is an easy add to your rotation.

Consider a Vitamin D3 supplement (with K2) — Most people benefit from 2,000–5,000 IU daily during fall and winter. Vitamin D3 is the form your body produces naturally from sunlight and is more effective than D2. K2 helps your body use the D3 properly by directing calcium to your bones instead of soft tissues. Check with your doctor and consider getting your levels tested so you know your baseline, but don’t wait months to feel better if this is the missing piece. Supplementation isn’t a sign of failure — it’s meeting your body where it actually is.

Light therapy in the morning — A 10,000-lux light therapy box for 20–30 minutes can mimic natural sunlight and help reset your circadian rhythm. Sit about 16–24 inches away from the light while you have coffee or read emails. It’s not a cure-all, but for some people dealing with Seasonal Affective Disorder (SAD), it’s a game-changer. Look for a box that’s specifically designed for SAD treatment and emits 10,000 lux at the recommended distance. You can find quality options for under $50.

Track how you feel — Notice patterns. If you feel worse in winter every year — lower energy, more irritability, less motivation — that’s data. Keep a simple log of your mood and energy levels for two weeks. Bring it to your doctor and ask for a Vitamin D test. Having concrete data makes it easier to advocate for the support you need. Too many high-performers dismiss their own experience because they don’t have “evidence.” Your lived experience is evidence.

You don’t have to do all of this at once. Pick one thing. Try it for a week. See what shifts.

⚠️ Reality Check: Even with all these strategies, some people will still struggle with seasonal mood changes. If you’ve optimized your Vitamin D, tried light therapy, and you’re still feeling significantly low, talk to your doctor. Sometimes seasonal depression requires additional support, whether that’s therapy, medication, or a combination. There’s no shame in getting help — it’s actually the smartest move you can make.

Making It Stick

The key to making these practices stick is attaching them to something you’re already doing. If you have morning coffee, do it by a window or take your mug outside for 10 minutes. If you check emails first thing, do it next to your light therapy box. If you meal prep on Sundays, add salmon or eggs to your rotation.

The less friction, the more likely you’ll keep doing it.

Over time, you’ll notice shifts that go beyond just “feeling better.” Your sleep may improve because your circadian rhythm is more regulated. Your afternoon slumps may disappear because your body is producing serotonin more efficiently. You might find that you’re more patient, more present, and more like the version of yourself you recognize.

After 2–4 weeks of consistent practice, these changes often become self-reinforcing — you keep doing them because they work, not because you’re forcing yourself to.

Coach’s Note

I’ve noticed in my own journey that winter used to hit me hard — brain fog, low energy, the whole thing. Once I started paying attention to Vitamin D and morning light, it completely shifted. I’m not saying winter is easy now, but I’m not white-knuckling my way through it anymore.

You’re not imagining this. And you’re not failing at resilience. Sometimes the answer isn’t mindset — it’s meeting your body where it actually is. You’re closer to feeling like yourself again than you think.

If this hit home, save it for later. Share it with someone who might need to hear it. And if you want support figuring out what’s getting in the way of your energy and focus, I have a few openings for 1:1 coaching. DM me — I’d love to hear what’s showing up for you.