December is supposed to feel magical — yet somehow it’s also the month when everyone is exhausted, overstimulated, emotional, and running on fumes.

But here’s the truth most people don’t realize:

Your hormones literally shift in December.
Not metaphorically. Not emotionally.
Physically. Biochemically. Measurably.

And once you understand what’s happening inside your body, the holiday “why do I feel like this?” finally makes sense.

Let’s break down what’s actually going on.

Shorter Days = Your Cortisol Rhythm Gets Thrown Off

Cortisol gets a bad reputation, but you need it.
It helps you wake up, stay focused, and handle stress.

But in December?

• Later sunrise → delayed cortisol awakening response
• Less sunlight → weaker signal to your brain
• Holiday stress → cortisol spikes at the wrong time

So instead of this:

High in the morning, low at night

You get this:

Low in the morning, HIGH at night.

Which feels like:

• Waking up groggy
• Afternoon crashes
• Nighttime anxiety
• Difficulty falling asleep
• Feeling “wired but tired”

This isn’t a mindset issue — it’s physiology.

Less Sunlight = Lower Serotonin (Your Mood + Appetite Hormone)

Serotonin is your natural “I’m okay” chemical.
It stabilizes mood, supports digestion, and helps regulate appetite.

But shorter days = less light hitting your retina = less serotonin production.

Low serotonin can show up as:

• Irritability
• Low motivation
• Emotional eating
• Sugar and carb cravings
• Anxiety or mental fatigue

This is also why December suddenly makes you crave pasta, bread, desserts, and salty snacks.
Your brain is trying to self-medicate with the fastest serotonin boosters: carbs + sugar.

Melatonin Rises Earlier — And Makes You Feel Off

The darker it gets, the earlier melatonin rises. But when melatonin increases too soon, you feel:

• Sleepy at the wrong time
• Moody
• Foggy
• Disconnected
• Less productive

This early melatonin spillover also suppresses dopamine — the motivation and drive hormone.

So if December feels like “I can’t get myself to do anything”… it’s not you. It’s your neurochemistry adjusting to winter.

Stress + Overstimulation = Cortisol + Insulin Imbalance

Holiday expectations + social events + money stress + travel = your stress hormones working overtime.

When cortisol stays elevated:

• Blood sugar spikes
• Insulin increases
• You crave more carbs
• You store more fat (especially belly fat)
• You feel hungrier, even after eating

This combo is what makes December feel like:
“I want to stop eating junk but my body is requesting it.”

Emotional Eating Isn’t a Lack of Willpower — It’s Biology

Low sunlight + high stress + altered circadian rhythm = your brain seeking comfort.

Food becomes a quick dopamine hit because:

• Dopamine drops in winter
• Serotonin dips
• Cortisol rises
• Melatonin disrupts appetite cues

This mix leads to:

• Comfort eating
• Snacking when bored
• Craving sweets after dinner
• Eating to “feel normal”

It’s not a personality flaw. It’s a hormonal stress response.

So… How Do You Balance Your Hormones in December?

Here are functional medicine basics that make a big difference:

Get morning sunlight in your eyes

10 minutes helps reset cortisol and serotonin.

Keep your mornings predictable

Your hormones love routine: hydration, protein, light.

Prioritize protein + whole foods early in the day

Helps steady serotonin and blood sugar.

Move your body daily

Not intense — just consistent (walks, stretching, light strength).

Reduce blue light at night

If you love Christmas lights, turn off the bright white LED ones and switch to warm tones.

Don’t skip meals

This worsens cortisol spikes → cravings → overeating later.

Normalize rest

Force breaks. Say no to overstimulation.

The Bottom Line

If December makes you feel:

✔ more tired
✔ more emotional
✔ more hungry
✔ more irritable
✔ more overwhelmed
✔ more “off”
✔ more like hiding from social events

…it’s not all “holiday stress.”

It’s your cortisol, melatonin, serotonin, insulin, and dopamine shifting with the season.

Your hormones respond to light — and December changes everything.

When you understand this, the holidays feel less confusing…
and you can support your body instead of pushing against it.

Sources

• Lambert GW et al. Effect of sunlight on serotonin levels. The Lancet.
• Lewy AJ. Melatonin and winter mood changes. Archives of General Psychiatry.
• Goldstein-Piekarski et al. Cortisol rhythms and sleep disruption. Sleep Medicine Reviews.
• Boden G. Effects of stress and cortisol on insulin resistance. Endocrine Practice.
• Rosenthal NE. Seasonal changes in mood and behavior. New England Journal of Medicine.