Vitamin D: The Complete Guide

Look, I dropped 17kg in 6 months with 36-hour weekend fasts, and vitamin D was a game-changer. Not because it's some magic weight loss pill—it's not. But because when you're deficient (and 42% of people are), everything feels harder. Your energy tanks, your mood crashes, and those 36-hour fasts become absolute misery instead of the sustainable approach they should be.

This isn't about expensive supplements or complicated protocols. It's about understanding what vitamin D actually does, why most people are deficient, and how to fix it with real, evidence-based strategies that actually work.

Skip & Fuel Hack: During my transformation, getting my vitamin D levels right was crucial. No more winter blues, better energy during fasts, and my immune system actually worked. The difference was night and day.

What Is Vitamin D and Why Should You Care?

Vitamin D isn't just another supplement to add to your stack. It's a hormone that your body makes when sunlight hits your skin, and it affects nearly every system in your body. Think of it as the conductor of your body's orchestra—when it's out of tune, everything sounds off.

The shocking truth: 42% of people are deficient, and most don't even know it. You could be feeling tired, moody, and run down not because you're lazy or unmotivated, but because you're simply not getting enough vitamin D.

The Two Types That Matter

Vitamin D3 (Cholecalciferol): The good stuff. Made in your skin from sunlight, found in animal foods
Vitamin D2 (Ergocalciferol): The weaker version. Found in some plants and fortified foods

Skip & Fuel Reality Check: D3 is what you want. It's more effective, stays in your body longer, and actually works. Don't waste your money on D2 supplements.

Why You're Probably Deficient (And Don't Know It)

Here's the thing about vitamin D deficiency—it's sneaky. You don't wake up one day with rickets like they did in the 1800s. Instead, you just feel... off. Tired all the time, moody, getting sick more often, maybe some muscle aches.

The modern lifestyle is killing your vitamin D:

Working indoors all day
Wearing sunscreen (which blocks vitamin D production)
Living in northern climates
Having darker skin (needs more sun exposure)
Being overweight (vitamin D gets trapped in fat)

Skip & Fuel Insight: During my weight loss journey, I realized I'd been deficient for years. I thought I was just "not a morning person" and "prone to winter blues." Nope—I was just vitamin D deficient. Getting my levels right changed everything.

What Vitamin D Actually Does in Your Body

Vitamin D isn't just about strong bones—though that's important too. It's involved in so many processes that when you're deficient, everything feels harder.

1. Immune System Support

Your immune system has vitamin D receptors everywhere. When you're deficient, you get sick more often, take longer to recover, and your body struggles to fight off infections.

Skip & Fuel Reality: During my 36-hour fasts, I used to get sick constantly. Turns out, I was vitamin D deficient. Once I fixed it, I could fast without getting run down or catching every cold that went around.

2. Mood and Mental Health

Vitamin D helps regulate serotonin (your "feel good" hormone). Low levels are linked to depression, anxiety, and seasonal affective disorder.

3. Muscle Function

Ever feel weak or get muscle cramps? Vitamin D deficiency can cause muscle weakness and pain. It's essential for muscle contractions and strength.

4. Bone Health

This is the classic one—vitamin D helps your body absorb calcium. Without it, your bones get weak and brittle.

5. Heart Health

Vitamin D helps regulate blood pressure and supports cardiovascular function. Deficiency is linked to higher risk of heart disease.

6. Weight Management

Here's where it gets interesting for weight loss. Vitamin D deficiency is linked to insulin resistance, which makes it harder to lose weight and easier to gain it.

Skip & Fuel Insight: This was a game-changer for me. Once I got my vitamin D levels up, my insulin sensitivity improved, and the weight started coming off more easily. It wasn't magic, but it removed a major roadblock.

The Real Signs You're Deficient

Most people think vitamin D deficiency means weak bones, but the signs are way more subtle and common than you'd think:

Physical Symptoms:

Constant fatigue (even with enough sleep)
Muscle weakness or aches
Bone pain or back pain
Getting sick frequently
Slow wound healing
Hair loss

Mental/Emotional Symptoms:

Depression or low mood
Anxiety
Brain fog or difficulty concentrating
Irritability
Seasonal depression (winter blues)

Skip & Fuel Reality Check: I had most of these symptoms for years and just thought I was "stressed" or "getting older." Turns out, I was just vitamin D deficient. The fatigue alone was killing my motivation to stick with my fasting routine.

The sneaky part: These symptoms can be so gradual that you don't even notice them until they're gone. You just think "this is how I am" when really, you're just deficient in a crucial nutrient.

How Much Vitamin D Do You Actually Need?

Here's where it gets confusing because the official recommendations are way too low for most people.

The official recommendations (way too low):

Adults: 600-800 IU per day
Elderly: 800-1000 IU per day

What you actually need (based on real research):

Maintenance: 2000-4000 IU per day
Deficiency treatment: 5000-10000 IU per day for 8-12 weeks
Severe deficiency: 10000+ IU per day under medical supervision

Skip & Fuel Reality: The official recommendations are based on preventing rickets, not optimizing health. Most people need 3-5x more than the official recommendations to feel their best.

Blood Level Targets (This Is What Matters)

Deficient: Under 20 ng/mL (you feel terrible)
Insufficient: 20-30 ng/mL (you feel okay but not great)
Adequate: 30-50 ng/mL (you feel decent)
Optimal: 50-80 ng/mL (you feel amazing)
Toxic: Over 100 ng/mL (dangerous)

The goal: Get to 50-80 ng/mL and stay there. Most people need 3000-5000 IU daily to maintain this level.

The Cofactors That Actually Matter

Vitamin D doesn't work alone. It needs other nutrients to do its job properly. Skip the cofactors, and you're basically throwing money away.

1. Magnesium (The Most Important)

Required for vitamin D activation
Most people are deficient in both
Take 200-400mg magnesium with your vitamin D
Skip & Fuel Hack: I take magnesium glycinate at night—better sleep and better vitamin D function

2. Vitamin K2 (MK-7)

Prevents calcium from building up in your arteries
Directs calcium to your bones where it belongs
Take 100-200mcg daily
Skip & Fuel Reality: Without K2, vitamin D can actually make your arteries stiffer. Not what we want.

3. Healthy Fats

Vitamin D is fat-soluble—it needs fat to be absorbed
Take it with a meal that contains fat
Skip & Fuel Tip: I take mine with my morning coffee (with cream) or with dinner

4. Zinc

Supports vitamin D receptor function
Most people are also zinc deficient
Take 8-15mg daily

Skip & Fuel Insight: I learned this the hard way. I was taking vitamin D for months and felt no difference. Once I added magnesium and K2, everything changed. The vitamin D actually started working.

How to Get Vitamin D (The Right Way)

1. Sunlight (The Natural Way)

Get 10-30 minutes of midday sun on bare skin
No sunscreen (it blocks vitamin D production)
More time needed if you have darker skin
Skip & Fuel Reality: This is hard in winter or if you work indoors. I supplement year-round and get sun when I can.

2. Food Sources (Limited but Important)

Fatty fish (salmon, sardines, mackerel)
Egg yolks
Fortified foods (milk, some cereals)
Skip & Fuel Tip: I eat salmon 2-3 times per week, but it's still not enough to meet your needs

3. Supplements (The Practical Choice)

Vitamin D3 (not D2)
Take with fat for better absorption
Start with 2000-4000 IU daily
Get your blood tested after 8-12 weeks

Skip & Fuel Hack: I take 5000 IU of D3 with my morning coffee (cream provides the fat). Simple, effective, and I don't have to think about it.

The Supplement Quality Trap

Not all vitamin D supplements are created equal. Here's what to look for:

What to Avoid

Vitamin D2 (less effective)
Cheap, generic brands (often underdosed)
Tablets without fat (poor absorption)
Mega-doses (10,000+ IU without testing)

What to Look For

Vitamin D3 (cholecalciferol)
Third-party tested (NSF, USP, or ConsumerLab)
Softgels or liquid (better absorption)
Reasonable dosing (2000-5000 IU)

Skip & Fuel Reality: I wasted money on cheap supplements for months. Once I switched to a quality D3 with K2, the difference was immediate. Don't cheap out on your health.

My Simple Stack

5000 IU D3 (with breakfast)
200mg Magnesium Glycinate (at bedtime)
100mcg K2-MK7 (with breakfast)
15mg Zinc (with dinner)

Total cost: About $30/month for everything. Way cheaper than feeling like crap.

When to Get Tested (And What to Ask For)

Get tested if you:

Feel tired, moody, or run down
Get sick frequently
Have muscle aches or weakness
Live in a northern climate
Work indoors most of the time
Have darker skin
Are overweight

What to ask for:

25(OH)D test (not 1,25(OH)D)
ng/mL units (not nmol/L)
Target range: 50-80 ng/mL

Skip & Fuel Reality: I got tested after feeling terrible for months. My level was 18 ng/mL—severely deficient. No wonder I felt like crap during my fasts.

How often to test:

First time: After 8-12 weeks of supplementation
Maintenance: Every 6-12 months
Adjustment: If you change your dose significantly

Cost: Usually $50-100, often covered by insurance. Worth every penny.

The Bottom Line

Vitamin D deficiency is sneaky, common, and fixable. Most people are walking around feeling terrible because they're deficient in a nutrient that costs pennies per day to fix.

Here's what you need to know:

42% of people are deficient (probably including you)
Official recommendations are too low (aim for 50-80 ng/mL)
You need cofactors (magnesium, K2, zinc)
Quality matters (don't cheap out on supplements)
Get tested (it's the only way to know for sure)

Skip & Fuel Reality: Getting my vitamin D levels right was one of the best things I did for my health and my fasting routine. No more winter blues, better energy, stronger immune system. It's not magic, but it removes a major roadblock to feeling your best.

The simple approach:

Get tested (25(OH)D, aim for 50-80 ng/mL)
Take 3000-5000 IU D3 daily (with fat)
Add magnesium and K2 (they're essential)
Retest in 8-12 weeks (adjust as needed)
Maintain optimal levels (test every 6-12 months)

Total investment: About $30/month for supplements, $50-100 for testing. Way cheaper than feeling like crap and way more effective than most expensive "health" products.

The cravings? They ghosted me by week 3 when I got my vitamin D levels right. Real people need real nutrition, not expensive supplements that don't work.

Ready to Try It Yourself?

This is exactly the approach I used to drop 17kg—36-hour weekend fasts (Friday 8pm to Sunday 8am), keto refueling on Sundays, and zero misery. The Skip & Fuel app will help you track it all, with electrolyte reminders and real support.

Join the waitlist to be first in line when we launch.

About the Author: Skip & Fuel was created by someone who lost 17kg in 6 months using the 36-hour weekend fasting approach. Real results, real strategies—no BS.

Vitamin D: The Complete Guide to Benefits, Deficiency & Supplementation