The Vitamin D Problem in Winter

In the Northern Hemisphere (especially above ~40° latitude), UVB rays are too weak from roughly October to March to trigger meaningful vitamin D synthesis in the skin.

So unless one:

• eats vitamin D–rich foods (fatty fish, egg yolks, liver, cod liver oil), or
• uses supplements,

blood 25(OH)D levels will steadily drop during winter.

Did We Evolve to Handle This?

Yes, but not necessarily in the “optimal modern health” sense.

Evolutionary adaptation:

Before supplements, northern populations survived winters with seasonally lower vitamin D levels, but also had:

• Higher intake of animal fats and fish liver (traditional Arctic and Nordic diets are loaded with D, A, and omega-3s).
• Reduced metabolic demand — slower pace of life, less activity, shorter days.
• Greater reliance on stored D in body fat from the summer months.
• Physiological downshifting: thyroid and reproductive hormones adapt to darker months (mild “winter torpor,” not true hibernation).

So yes, the body partially adapts, but it was always accompanied by diet and lifestyle patterns that supported that adaptation.

Winter is High Melatonin and Low Vitamin D: Recalibration

In winter, longer nights and lower UV exposure make melatonin levels rise for several months.

That’s not a deficiency — it’s a seasonal recalibration.

Melatonin slows metabolism and cellular turnover, allowing repair and immune regulation.

Because energy use is reduced, your body requires less vitamin D for calcium metabolism, immunity, and mitochondrial activity.

It’s like switching from “growth and reproduction mode” to “maintenance and restoration mode.”

Recent research (PMID: 39488920) shows that melatonin and vitamin D:

• Share nuclear receptor crosstalk (e.g. VDR and RORα/β receptors).
• Regulate each other’s synthesis enzymes in mitochondria.
• Act as antioxidants and immune modulators in similar ways.
• Have synergistic effects on inflammation control, mitochondrial protection, and fertility regulation.

In winter, elevated melatonin partly substitutes for vitamin D’s anti-inflammatory and antioxidant roles.

Your physiology doesn’t need to maintain high D levels because melatonin is covering part of that job.

What “Adaptation” Means Functionally

Here’s how your body compensates naturally for less sunlight:

Function	Seasonal Adaptation
Calcium metabolism	Body may become more efficient at reusing calcium, slowing bone turnover.
Thyroid activity	T3 naturally drops in winter → lower metabolism → less D use.
Melatonin	Increases with darkness → modulates immune system and energy use.
Immune function	Certain immune pathways ramp up independent of D (cold adaptation).
Mitochondria	Shift from UV-driven metabolism to more brown fat thermogenesis (heat production).

So “adapting” doesn’t mean you no longer need vitamin D: it means your physiology is recalibrating energy and hormonal priorities for winter.

The “Hibernation” Parallel

Humans don’t truly hibernate, but we do have a circannual rhythm (an annual metabolic pattern shaped by light exposure, temperature, and food availability).

Low light and low D are signals to:

1. Sleep more and conserve energy,
2. Increase melatonin and brown fat activity,
3. Shift from growth/reproduction toward repair and preservation.

If we align with this rhythm (sleep earlier, eat more warming fats, avoid artificial light late at night), our need for supplements may decrease somewhat, because our metabolism becomes more efficient under “winter mode.”

Functional Ways to Reduce Dependence on Vitamin D Supplements

To teach your body the right “information” for seasonal adaptation, think in terms of environmental coherence:

Light

• Get morning sunlight daily (even weak light entrains circadian rhythms).
• Use bright white or red-infrared light therapy in the morning if you live far north — not to make D directly, but to mimic daylight cues and support endocrine balance.
• Avoid strong artificial light at night (it blocks melatonin).

Diet

• Eat seasonally appropriate fats:
  • Fatty fish (herring, salmon, mackerel, sardines)
  • Pastured butter, egg yolks, cod liver oil (natural D and A synergy)
  • Liver once a week (vitamin A helps D function)
• Keep magnesium, zinc, and K2 sufficient: these are D cofactors.

Temperature

• Cold exposure (walks in snow, lukewarm showers) activates brown fat and improves mitochondrial efficiency, part of the natural winter adaptation.

Rest & Circadian rhythm

• Earlier sleep, slower evenings, candlelight/dim light cues signal “winter mode.”
• This lowers cortisol and energy demand, so less D is consumed.

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Your body can adapt to less sunlight if:

1. You live seasonally (light, sleep, diet, pace),
2. You nourish yourself with ancestral nutrient sources,
3. And you reduce modern mismatches (nighttime light, constant stress, processed foods).

Supplements remain useful — but the goal isn’t to override winter; it’s to thrive within it.

your adaptation plan

Light Management: Teaching the Body It’s Winter

Morning

• Go outside within 30 min of waking, even if cloudy.
  → 10–15 min is enough to signal the hypothalamus and stabilise serotonin, thyroid, and cortisol.
• If mornings are pitch-dark:
  → Use a 10,000 lux daylight lamp for 20 min during breakfast.
  → Alternatively, a red/infrared light panel on face and chest for 5–10 min.

Daytime

• Keep curtains open — natural light intensity, even grey, is 100× stronger than indoor light.

Evening

• Dim everything 2 h before bed.
  → Use amber light or candles, never bright white LEDs.
  → This boosts melatonin, helping immunity, fertility, and mitochondrial repair.

Night

• Aim for 8–9 hours of sleep, or earlier bedtime (21:30–22:00).
  Winter is for rest and hormone recalibration.

Nutrition: Eating Like Winter Was Meant To Be

Core principles:

1. Warm, fatty, mineral-rich, and animal-based.
2. Lower in tropical foods (no summer signals: pineapples, citrus excess, etc.).
3. Focus on fat-soluble vitamins D, A, and K2 synergy.

Daily nourishment template:

Meal	What to focus on
Breakfast	Warm, grounding: eggs in butter, mushrooms, sourdough toast, broth, or porridge with cream.
Lunch	Fatty fish or meat stew with root vegetables (carrots, parsnips, celery root).
Dinner	Slow-cooked meats, soups, fermented veggies, ghee or butter, small starch portion.
Snacks	Liver pâté, cheese, cod liver oil (small spoon), nuts if tolerated, dark chocolate.

Key foods for natural vitamin D and cofactors:

• Cod livers (they come in tin cans): ½–1 tsp daily (balanced D + A + omega-3s).
• Herring, mackerel, salmon: 2–3× weekly.
• Egg yolks: daily.
• Liver: 1× weekly.
• Raw butter / aged cheese: daily (K2 + saturated fat synergy).
• Oysters or red meat: for zinc and magnesium.

→ These foods signal winter survival mode: dense, warming, nutrient-rich.

Supplementation — Smart, Minimal, Synergistic

Nutrient	Dose	Form	Why
Vitamin D3	1000–2000 IU 3–4x/week (not daily)	With K2	Just enough to prevent severe dip, not override seasonality
Vitamin A (retinyl palmitate or liver)	Through food or supplement 2500–5000 IU	Balances D and supports immunity
Magnesium glycinate	150–300 mg nightly	Helps D activation + sleep
Vitamin K2 (MK-7)	90–120 µg	Directs calcium correctly
Cod liver oil	Optional ½–1 tsp daily	Natural D + A + DHA source
Trace minerals (zinc, selenium)	Via food or minimal supplement	Thyroid, fertility, immune support

Temperature Adaptation — Brown Fat & Mitochondrial Training

Practice	Frequency	Benefits
Cold walks (5–20 min)	3–5× per week	Improves circulation, thermogenesis
Contrast showers	Finish warm showers with 30–60 sec lukewarm	Brown fat activation
Sauna (if available)	1–2× weekly	Mimics ancient winter heat exposure, detox, cardiovascular fitness

These practices tell your mitochondria: “We are in winter; time to run clean, efficient energy production.”

Rhythm and Lifestyle

Element	Practice	Why
Movement	Slow strength, yoga, winter walks, breath-work	Keeps metabolism and lymph moving without excess cortisol
Stress reduction	Meditation, warm baths, journaling	High stress = more vitamin D consumption
Creativity & reflection	Reading, art, planning	Winter is inner work season
Avoid overstimulation	No late scrolling, caffeine reduction	Supports circadian recalibration

Signs of Successful Adaptation

You’ll notice:

• Fewer sugar cravings
• More stable mood despite less sun
• Deep sleep, vivid dreams
• Warm hands/feet even in cold
• Steady energy without needing caffeine
• Mild, steady hunger (not extremes)

These indicate your mitochondria and hormones have synchronized with winter mode.

Spring Transition (March–April)

When daylight strengthens:

• Increase outdoor light exposure
• Reduce cod liver oil gradually
• Reintroduce fresh greens and lighter meals
• Extend daytime activity
• Begin more active training

You move from “repair and rest” to “growth and creation.”

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Has this been a fun article? Let me know how are you planning your winter rhythm and don’t hesitate to send me any question regarding this topic on my Instagram! :)

Also, I have a follow-up article on proper Vitamin D supplementation! Don’t miss it. Read it here.