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Vitamins

The 13 essential vitamins your body needs but cannot make.

📖 The Story: Why Modern Deficiencies Are Invisible

Meet Sarah and Jennifer—both 35, both eating "healthy," both exhausted.

Sarah's doctor runs standard blood tests: everything normal. She's told to sleep more, stress less. But Sarah's vitamin D is 18 ng/mL (technically not "deficient" by some outdated cutoffs), her B12 is 250 pg/mL (low-normal but causing symptoms), and she's never been tested for folate, magnesium, or zinc. She feels terrible but has no diagnosis.

Jennifer takes a different approach. She requests specific nutrient testing and discovers her vitamin D is 18 ng/mL, her B12 is 220 pg/mL, and she has an MTHFR variant affecting folate metabolism. Six months of targeted supplementation later, her energy is back, her brain fog is gone, and she finally feels like herself again.

The same story, different outcomes. The difference? Understanding that modern vitamin problems aren't about scurvy or rickets—they're about subclinical insufficiency: levels low enough to impair optimal function but not low enough to trigger obvious disease.

In 1912, Casimir Funk discovered that certain diseases were caused by the absence of something in food. He called these substances "vitamines." That discovery ended epidemics of beriberi, scurvy, pellagra, and rickets.

Today's challenge is subtler. You won't get scurvy eating a modern diet. But you might have:

  • Vitamin D at 22 ng/mL instead of optimal 40-60 ng/mL
  • B12 at 300 pg/mL instead of optimal 500+ pg/mL
  • Folate issues hidden by MTHFR variants affecting 40-50% of people

The result? Fatigue, brain fog, mood issues, frequent illness, slow recovery—symptoms that get blamed on aging, stress, or "just life."

The 13 essential vitamins don't provide calories, but without them, you can't convert food to energy, build tissues, fight infections, or perform the thousands of biochemical reactions that make you feel alive.

🚶 The Journey: How Vitamins Get From Food to Function

When you eat a colorful salad with salmon, your body begins an intricate sorting and delivery process. Here's what happens:

Stage 1: Liberation (Mouth → Stomach)​

What happens: Chewing breaks food apart. Stomach acid releases vitamins from food proteins and fibers.

Why it matters:

  • Low stomach acid (common with age, PPIs, stress) = poor vitamin release
  • This is why older adults often absorb B12 poorly—it's stuck in food proteins
  • Fat-soluble vitamins (A, D, E, K) begin separating into fat droplets

Stage 2: Preparation (Small Intestine - Upper)​

What happens: Pancreatic enzymes and bile prepare vitamins for absorption.

The fat-soluble vitamin process:

Why fat matters: Without dietary fat, fat-soluble vitamins pass right through you. That fat-free salad dressing? Your body barely absorbs the vitamins from your vegetables.

Stage 3: Absorption (Small Intestine - Various Locations)​

Different vitamins have specific absorption sites:

LocationVitamins AbsorbedWhat Can Go Wrong
DuodenumIron, calcium, folateCeliac damage, bypass surgery
JejunumA, D, E, K, most B vitaminsCrohn's disease, infection
IleumB12 (requires intrinsic factor)Crohn's, resection, pernicious anemia
Whole intestineVitamin CGenerally resilient

B12's special journey: B12 must bind to Intrinsic Factor (made by stomach) to be absorbed in the ileum. This is why B12 deficiency is so common—failure at any step blocks absorption.

Stage 4: Transport (Blood & Lymph)​

Water-soluble vitamins (B, C): Enter bloodstream directly → travel to liver → distributed to cells

Fat-soluble vitamins (A, D, E, K):

  • Packaged into chylomicrons → enter lymphatic system → eventually reach bloodstream
  • Stored in liver and fat tissue (this is why toxicity is possible)

Stage 5: Cellular Use & Storage​

Practical implications:

  • Fat-soluble: Don't need daily intake, but can build up to toxic levels
  • Water-soluble: Need regular intake, but excess is simply excreted (usually)
  • B12: The exception—years of storage, but once depleted, symptoms appear
🧠 The Science: Understanding Vitamins

The 13 Essential Vitamins​

Fat-Soluble vs. Water-Soluble: Key Differences​

PropertyFat-Soluble (A, D, E, K)Water-Soluble (B, C)
StorageLiver, fat tissueMinimal (except B12)
Toxicity riskHigher (can accumulate)Lower (excreted in urine)
Intake frequencyDon't need dailyNeed regular intake
AbsorptionRequire dietary fatAbsorb directly
Deficiency timelineMonths to yearsWeeks to months

Fat-Soluble Vitamins​

Vitamin A (Retinol / Beta-Carotene)​

What it does:

  • Vision (rhodopsin for night vision, retinal health)
  • Immune function (epithelial barrier, immune cell development)
  • Cell growth and differentiation
  • Reproduction and fetal development
  • Skin health

Two forms:

  1. Preformed vitamin A (retinol) — Found in animal foods, directly usable
  2. Provitamin A (beta-carotene) — Found in plants, must be converted

Conversion efficiency: Beta-carotene → Retinol is only 12:1 (you need 12 mcg beta-carotene to get 1 mcg retinol). Some people convert even more poorly due to genetics (BCMO1 gene variants).

caution

Don't mega-dose retinol supplements, especially during pregnancy. Beta-carotene from food is safe—your body regulates conversion.

Vitamin D (Cholecalciferol / Ergocalciferol)​

What it does:

  • Calcium and phosphorus absorption (essential for bones)
  • Bone mineralization and remodeling
  • Immune function (both innate and adaptive immunity)
  • Muscle function
  • Cell growth regulation
  • Mood and brain function

Two forms:

  1. D3 (cholecalciferol) — From animal sources and sun exposure; more effective
  2. D2 (ergocalciferol) — From plants/fungi; less potent, shorter-acting

The "sunshine vitamin": Your skin synthesizes D3 when exposed to UVB rays. However, synthesis is impaired by:

  • High latitude (above ~35°N in winter)
  • Dark skin (melanin blocks UVB)
  • Sunscreen (SPF 15 blocks 93% of UVB)
  • Age (elderly produce 75% less)
  • Indoor lifestyle
For Mo

Most people need D3 supplementation, especially those with limited sun exposure, dark skin, or living at high latitudes. Test annually and supplement to reach 40-60 ng/mL.

Vitamin E (Tocopherols / Tocotrienols)​

What it does:

  • Primary antioxidant — Protects cell membranes from oxidative damage
  • Protects polyunsaturated fats (PUFAs) from lipid peroxidation
  • Immune function
  • Cell signaling
  • Cardiovascular health (prevents LDL oxidation)

Eight forms exist:

  • 4 tocopherols (alpha, beta, gamma, delta)
  • 4 tocotrienols (alpha, beta, gamma, delta)

Only alpha-tocopherol is maintained in blood by the liver. RDA is based on alpha-tocopherol only.

Natural vs. Synthetic:

  • Natural: d-alpha-tocopherol (better absorbed and retained)
  • Synthetic: dl-alpha-tocopherol (50% as bioavailable)

Vitamin K (Phylloquinone / Menaquinones)​

What it does:

  • Blood clotting — Activates clotting factors (II, VII, IX, X)
  • Bone health — Activates osteocalcin (puts calcium into bones)
  • Cardiovascular health — Activates matrix GLA protein (keeps calcium OUT of arteries)

Two main forms:

FormSourceFunction
K1 (Phylloquinone)Leafy greensPrimarily clotting
K2 (Menaquinones)Fermented foods, animal products, gut bacteriaClotting + bones + arteries

K2 subtypes:

  • MK-4 — Short half-life (hours); from animal foods
  • MK-7 — Long half-life (days); from natto, fermented foods; reaches bones/arteries better
tip

K2 (especially MK-7) is increasingly recognized as important for bone and cardiovascular health beyond clotting. Consider supplementing if not eating fermented foods or quality animal products.

Water-Soluble Vitamins​

The B Vitamins: Energy Metabolism Team​

The 8 B vitamins work together as coenzymes in energy metabolism. They're often found together in foods and supplements as "B complex."

Vitamin B1 (Thiamin)​

What it does:

  • Carbohydrate metabolism (pyruvate dehydrogenase)
  • Nerve function and muscle contraction
  • ATP production

RDA: 1.1-1.2 mg/day

Best sources: Pork, whole grains, legumes, fortified cereals, sunflower seeds

Deficiency:

  • Beriberi — Wet (cardiovascular) or dry (neurological)
  • Wernicke-Korsakoff syndrome — In alcoholics (alcohol impairs absorption)
  • Symptoms: fatigue, irritability, poor memory, muscle weakness

At-risk: Alcoholics, elderly, bariatric surgery patients, those with HIV

Vitamin B2 (Riboflavin)​

What it does:

  • Coenzyme in energy metabolism (FAD, FMN)
  • Antioxidant (glutathione reductase)
  • Iron metabolism
  • Activates B6 and folate

RDA: 1.1-1.3 mg/day

Best sources: Dairy, eggs, lean meats, fortified cereals, mushrooms, almonds

Deficiency signs:

  • Cracked lips (cheilosis)
  • Sore throat
  • Inflamed tongue (glossitis)
  • Skin rashes
  • Anemia

Fun fact: Riboflavin turns urine bright yellow (harmless)

Vitamin B3 (Niacin)​

What it does:

  • Coenzyme in 400+ metabolic reactions (NAD, NADP)
  • Energy production
  • DNA repair
  • Cell signaling

Two forms:

  • Nicotinic acid — Causes flushing at high doses; lowers cholesterol
  • Niacinamide (nicotinamide) — No flushing; no cholesterol effect

RDA: 14-16 mg NE (niacin equivalents)

Best sources: Poultry, fish, beef, peanuts, mushrooms, fortified grains

Deficiency (Pellagra): The "4 D's" — Dermatitis, Diarrhea, Dementia, Death

Toxicity: High-dose nicotinic acid (>35 mg) causes flushing, liver damage, glucose elevation

Vitamin B5 (Pantothenic Acid)​

What it does:

  • Component of Coenzyme A (CoA) — central to all macronutrient metabolism
  • Fatty acid synthesis
  • Cholesterol and hormone synthesis
  • Neurotransmitter production (acetylcholine)

AI: 5 mg/day

Best sources: Widespread in food ("pantothenic" = "from everywhere"). Liver, mushrooms, avocado, eggs, chicken, whole grains.

Deficiency: Extremely rare. "Burning feet syndrome" (paresthesia)

Vitamin B6 (Pyridoxine)​

What it does:

  • Protein metabolism (over 100 enzyme reactions)
  • Neurotransmitter synthesis (serotonin, dopamine, GABA)
  • Hemoglobin production
  • Immune function
  • Homocysteine metabolism

RDA: 1.3-1.7 mg/day (increases with age)

Best sources: Poultry, fish, potatoes, bananas, chickpeas, fortified cereals

Deficiency signs:

  • Peripheral neuropathy
  • Dermatitis, cracked lips
  • Depression, confusion
  • Weakened immunity
  • Anemia

Toxicity: High doses (>100 mg/day long-term) cause sensory neuropathy

At-risk: Alcoholics, elderly, those on certain medications, kidney disease

Vitamin B7 (Biotin)​

What it does:

  • Coenzyme for carboxylases (fat, carb, protein metabolism)
  • Gene regulation
  • Cell signaling

AI: 30 mcg/day

Best sources: Egg yolks, liver, nuts, seeds, salmon, avocado, sweet potato

Deficiency: Rare (gut bacteria produce some biotin). Signs: hair loss, skin rashes, brittle nails, neurological symptoms.

Caution: Raw egg whites contain avidin, which binds biotin. Cooking denatures avidin.

Lab interference: High-dose biotin supplements can interfere with lab tests (thyroid, troponin, hormone panels). Stop 2-3 days before testing.

Vitamin B9 (Folate / Folic Acid)​

What it does:

  • DNA synthesis and repair
  • Cell division (crucial for rapidly dividing cells)
  • Red blood cell formation
  • Neural tube development in pregnancy
  • Homocysteine metabolism (with B12, B6)

Forms:

  • Folate — Natural form in food
  • Folic acid — Synthetic form in supplements and fortified foods
  • Methylfolate (5-MTHF) — Active form; used by body directly
caution

Folate deficiency during pregnancy causes neural tube defects (spina bifida, anencephaly). Women of childbearing age should ensure adequate intake BEFORE conception.

Vitamin B12 (Cobalamin)​

What it does:

  • DNA synthesis (with folate)
  • Red blood cell formation
  • Nerve function (myelin synthesis)
  • Homocysteine metabolism
  • Energy metabolism

Unique among vitamins:

  • Only vitamin containing cobalt (mineral)
  • Only made by bacteria (not plants or animals)
  • Animals get it from gut bacteria or eating bacteria-contaminated food
  • Stored in liver (2-5 year supply) — deficiency takes years to develop

Forms:

  • Cyanocobalamin — Synthetic, stable, must convert to active forms
  • Methylcobalamin — Active form for methylation reactions
  • Adenosylcobalamin — Active form for energy metabolism
danger

Vegans absolutely must supplement B12. There are no adequate plant sources. Deficiency causes irreversible neurological damage if untreated.

Vitamin C (Ascorbic Acid)​

What it does:

  • Collagen synthesis — Essential for skin, tendons, blood vessels, bone
  • Antioxidant — Donates electrons to neutralize free radicals
  • Immune function — Supports various immune cells
  • Iron absorption — Converts non-heme iron to absorbable form
  • Neurotransmitter synthesis — Dopamine, norepinephrine
  • Carnitine synthesis — For fat metabolism
  • Regenerates vitamin E

Humans cannot make vitamin C (unlike most animals) due to a genetic mutation. We must get it from food.

Choline: The Forgotten Essential​

Choline is not officially a vitamin but was designated an essential nutrient in 1998. Most people don't get enough.

What it does:

  • Acetylcholine synthesis — Neurotransmitter for memory, muscle control
  • Cell membrane structure — Phosphatidylcholine is a major membrane component
  • Methylation — Methyl donor (like folate, B12)
  • Fat transport — Lipoproteins require phosphatidylcholine
  • Fetal brain development — Critical during pregnancy

Requirements:

GroupAI
Adult men550 mg
Adult women425 mg
Pregnancy450 mg
Lactation550 mg

Best sources:

FoodAmountCholine (mg)
Beef liver (3 oz)85g356
Egg (1 large)50g147
Beef (3 oz)85g97
Chicken breast (3 oz)85g72
Salmon (3 oz)85g75
Kidney beans (1/2 cup)90g45

90% of Americans don't meet AI. Eggs are one of the best sources.

For Mo

Choline is critical during pregnancy for fetal brain development, yet prenatal vitamins often contain little or none. Encourage egg consumption or supplementation.

Vitamin-Like Compounds​

These aren't classified as vitamins (body makes some, or not proven essential) but play important roles:

CompoundWhat It DoesFood SourcesNotes
CoQ10Energy production in mitochondria, antioxidantOrgan meats, beef, fatty fishProduction decreases with age; statins deplete it
CarnitineTransports fatty acids into mitochondriaRed meat, dairyBody makes it but may benefit from more
Alpha-Lipoic AcidAntioxidant, glucose metabolismSpinach, broccoli, organ meatsBoth fat and water soluble
InositolCell signaling, neurotransmitter functionFruits, beans, grainsUsed therapeutically for anxiety, PCOS
PQQMitochondrial biogenesisParsley, kiwi, papayaEmerging research on neuroprotection
👀 Signs & Signals: Reading Your Body

Your body gives signals when vitamins are low. These aren't diagnostic (see a doctor for testing), but they can point you toward areas to investigate.

General Deficiency Patterns​

SignalPossible Vitamin ConnectionWhat to Check
Fatigue, low energyB12, D, B1, ironBlood panel, D test
Brain fog, poor concentrationB12, D, B1, folateB12, MMA, homocysteine
Frequent illnessD, C, A, zincVitamin D level
Slow wound healingC, A, zincDietary intake
Hair lossD, B7 (biotin), iron, zincFull thyroid + nutrient panel
Brittle nailsB7, iron, proteinDietary assessment
Cracks at mouth cornersB2, B6, ironB vitamin status
Muscle cramps/weaknessD, magnesium, potassiumD level, electrolytes
Night blindnessARetinol/carotenoid levels
Bleeding gumsCDietary vitamin C
Tingling/numbnessB12, B6, B1B12, MMA test
Depression/low moodD, B12, folate, B6D, B12, homocysteine
Bone painD25-OH vitamin D

Visual Clues​

Who Should Get Testing​

Definitely test if you:

  • Follow a vegan/vegetarian diet → B12, D, iron, zinc
  • Are over 50 → B12, D
  • Have gut issues (Crohn's, celiac, IBS) → All fat-soluble, B12
  • Take PPIs or metformin → B12
  • Have dark skin or limited sun → D
  • Are pregnant/planning pregnancy → Folate, D, B12, iron
  • Experience persistent fatigue → D, B12, iron, thyroid

Useful tests:

  • Vitamin D: 25-hydroxyvitamin D (aim for 40-60 ng/mL)
  • B12: Serum B12 + methylmalonic acid (MMA) for early detection
  • Folate: Serum folate + homocysteine
  • Iron: Full iron panel (ferritin, serum iron, TIBC)
🎯 Making It Work: Practical Vitamin Strategies

The "Big 5" Vitamins to Focus On​

Most people eating a reasonable diet get enough of most vitamins. But five deserve special attention:

Why it matters: 40%+ of adults are insufficient. Affects immunity, mood, bones, muscles.

Target: 40-60 ng/mL blood level (most people need 2,000-4,000 IU D3/day to reach this)

Strategy:

  1. Get tested (25-OH vitamin D)
  2. If <30 ng/mL: Supplement 2,000-4,000 IU D3 daily with fat
  3. Retest in 3 months
  4. Consider adding K2 (MK-7) 100-200 mcg

Food sources help but rarely sufficient: Fatty fish, egg yolks, fortified foods

Timing & Absorption Tips​

VitaminBest TimeWith Food?Notes
D3MorningWith fatTake with largest meal
K2Any timeWith fatCan take with D3
B12MorningOptionalCan be energizing
B ComplexMorningWith foodReduces nausea, can be energizing
CSplit dosesOptionalLarge doses: split to improve absorption
IronEmpty stomachAloneTake with vitamin C, away from calcium/coffee

Food-First Framework​

Breakfast additions:

  • 2 eggs = 294 mg choline + B12 + A + D
  • Orange or berries = vitamin C

Lunch/dinner additions:

  • Dark leafy greens = folate + K1 + A (as carotenoids)
  • Fatty fish 2x/week = D + B12 + omega-3s
  • Colorful vegetables = C + A (carotenoids)

Weekly:

  • Liver (3-4 oz) once = B12, A, folate, choline superload
  • Natto or aged cheese = K2
📸 What It Looks Like: A Vitamin-Rich Day

Example Day: Hitting Key Vitamins from Food​

Breakfast:

  • 2 scrambled eggs with spinach (B12: 1.2 mcg, choline: 294 mg, A, K1, folate)
  • 1/2 avocado (folate: 81 mcg, E, K1)
  • Orange (C: 70 mg)

Lunch:

  • Salmon salad with mixed greens, bell peppers, olive oil dressing (D: 570 IU, B12: 4.8 mcg, C, E, K1, A)
  • Side of lentils (folate: 179 mcg)

Snack:

  • Handful of almonds (E: 6.8 mg)
  • Carrot sticks with hummus (A as beta-carotene)

Dinner:

  • Chicken thighs with roasted broccoli and sweet potato (B vitamins, C: 51 mg, A: 1,096 mcg)
  • Side of sauerkraut (K2 from fermentation)

Daily totals (approximate):

VitaminAmount% of RDA
A1,500+ mcg RAE167%+
C150+ mg167%+
D600+ IU100%+
E10+ mg67%
K200+ mcg150%+
B126+ mcg250%
Folate400+ mcg100%
Choline400+ mg90%

What's still needed: Vitamin D is borderline (sunny day helps, or supplement). K2 MK-7 specifically is low (natto or supplement helps).

Budget-Friendly Vitamin Day (~$8)​

Breakfast ($1.50):

  • 2 eggs, scrambled ($0.60)
  • Frozen spinach, sautéed ($0.40)
  • Orange ($0.50)

Lunch ($2.50):

  • Canned salmon on whole wheat ($1.50)
  • Bagged salad mix ($1.00)

Dinner ($4.00):

  • Chicken thighs ($2.00)
  • Frozen broccoli ($1.00)
  • Sweet potato ($1.00)

Vitamins covered: A, C, D (partial), E (partial), K1, B12, folate, choline Worth supplementing: D3 (~$0.03/day), possibly K2

🚀 Getting Started: 5-Week Vitamin Optimization Plan

Week 1: Assessment​

Tasks:

  • Track your current diet for 3 days (use an app like Cronometer to see vitamin intake)
  • List any symptoms that might be vitamin-related (fatigue, brain fog, frequent illness, etc.)
  • Identify your risk factors (vegan/vegetarian? Over 50? Gut issues? Medications?)
  • Schedule vitamin D and B12 blood tests if you have risk factors

Focus: Just observe—no changes yet

Week 2: Foundation Foods​

Add these daily:

  • 2 eggs (choline, B12, A, D)
  • 1 serving colorful vegetables (C, A as carotenoids)
  • 1 serving leafy greens (K1, folate)

Focus: Build vitamin-rich eating habits

Week 3: Targeted Additions​

Based on your situation:

If you're...Add this
EveryoneFatty fish 2x/week OR D3 supplement
Vegan/vegetarianB12 supplement (1,000 mcg methylcobalamin)
Over 50B12 supplement
Limited sunD3 supplement (2,000-4,000 IU)
Pregnant/planningPrenatal with methylfolate
Not eating eggsCholine supplement or liver 1x/week

Week 4: Optimization​

Review:

  • Get test results back (if ordered)
  • Adjust D3 dose based on blood level
  • Consider adding K2 MK-7 (100-200 mcg) if taking D3
  • Fine-tune timing (fat-soluble with meals, B vitamins in morning)

Week 5 & Beyond: Maintenance​

Ongoing habits:

  • Eggs most days (easy choline + B vitamins)
  • Fatty fish 2x/week OR supplement D3
  • Colorful vegetables daily
  • Leafy greens daily
  • Liver monthly (optional but powerful)
  • Retest vitamin D annually

Signs you've got it right:

  • Better energy
  • Fewer infections
  • Clearer thinking
  • Improved mood
🔧 Troubleshooting: Common Vitamin Problems

Problem 1: "I take vitamins but still feel tired"​

Possible issues:

  1. Wrong form: Taking folic acid when you need methylfolate (MTHFR variant)
  2. Poor absorption: Taking D without fat, or B12 with coffee
  3. Testing the wrong thing: Serum B12 looks "normal" but MMA is elevated
  4. Not the vitamin: Could be iron, thyroid, sleep, or other causes
  5. Dose too low: RDA prevents deficiency but may not optimize

Solutions:

  • Take fat-soluble vitamins with food containing fat
  • Switch to methylated forms (methylfolate, methylcobalamin)
  • Get comprehensive testing (MMA for B12, free T3/T4 for thyroid)
  • Work with a practitioner to investigate further

Problem 2: "I can't afford quality supplements"​

Priority order if budget is limited:

  1. D3 (~$5-10/year) — The highest-impact, lowest-cost supplement
  2. B12 (if vegan/over 50) (~$10-15/year)
  3. Food first for everything else (eggs, canned fish, frozen vegetables)

Budget tips:

  • Costco, Amazon Subscribe & Save for supplements
  • Skip the multivitamin—targeted supplements work better
  • Canned salmon is cheap vitamin D
  • Frozen vegetables retain vitamins and are affordable

Problem 3: "I'm vegan and worried about deficiencies"​

Non-negotiable supplements:

  • B12: 1,000 mcg methylcobalamin daily (NO plant sources exist)
  • D3: 2,000-4,000 IU (vegan D3 from lichen is available)

Monitor closely:

  • Iron (get ferritin tested)
  • Zinc (low bioavailability from plants)
  • Omega-3 DHA/EPA (algae-based supplements)
  • Iodine (if not using iodized salt)

Food strategies:

  • Fortified nutritional yeast for B vitamins
  • Mushrooms exposed to UV for some vitamin D
  • Legumes and leafy greens for folate
  • Consider algae-based DHA/EPA

Problem 4: "I have digestive issues and worry about absorption"​

Conditions affecting absorption:

  • Celiac/Crohn's: Fat-soluble vitamins, B12, iron, zinc most affected
  • Gastric bypass: B12, iron, calcium, D particularly affected
  • Low stomach acid (aging, PPIs): B12 from food (supplement form absorbs better)

Solutions:

  • Sublingual or liquid B12 (bypasses gut)
  • Higher doses of fat-soluble vitamins (under supervision)
  • Test levels regularly
  • Consider working with a gastroenterologist + dietitian

Problem 5: "I'm confused about what to take"​

The simplest approach for most people:

Start with:
├── D3 (2,000-4,000 IU) — almost everyone needs this
└── K2 MK-7 (100-200 mcg) — optional but synergistic with D

Add if applicable:
├── B12 — if vegan, vegetarian, over 50, or on PPIs/metformin
├── Methylfolate — if pregnant or planning, or known MTHFR variant
└── Omega-3 — if not eating fatty fish 2x/week

Skip:
├── Multivitamins — usually poor formulations, prefer targeted
├── Vitamin C mega-doses — food sources are plenty for most
└── Vitamin A (retinol) supplements — toxicity risk, get from food

Problem 6: "My doctor says my levels are 'normal' but I feel terrible"​

The difference between "normal" and "optimal":

VitaminLab "Normal"Optimal
D20-100 ng/mL40-60 ng/mL
B12200-900 pg/mL500+ pg/mL
Ferritin12-150 ng/mL50-100 ng/mL

What to do:

  • Ask for exact numbers, not just "normal"
  • Research optimal ranges (functional medicine ranges are often tighter)
  • Consider working with a practitioner who focuses on optimization
  • Trust your symptoms—"normal" doesn't always mean "optimal for you"
⚖️ Where Research Disagrees

Optimal Vitamin D Level​

The debate:

  • Institute of Medicine: 20 ng/mL is "sufficient"
  • Endocrine Society: 30 ng/mL minimum, 40-60 ng/mL preferred
  • Some researchers: 40-60 ng/mL for optimal immune and bone function

Evidence:

  • Bone health clearly benefits from 30+ ng/mL
  • Immune function may benefit from higher levels
  • Very high levels (>100 ng/mL) show no additional benefit and possible harm

Practical stance: Aim for 40-60 ng/mL. This is safely above any "deficient" cutoff and associated with best outcomes in most studies.

Folic Acid vs. Methylfolate​

The debate:

  • Folic acid is well-studied and effective for neural tube defect prevention
  • Methylfolate may be better for those with MTHFR variants
  • Some concern about unmetabolized folic acid in blood

Evidence:

  • Folic acid clearly prevents neural tube defects
  • Methylfolate works for MTHFR variants who don't convert well
  • Studies on UMFA risks are mixed

Practical stance: Methylfolate is a reasonable choice for everyone and necessary for those with MTHFR variants. It's becoming the standard in quality supplements.

High-Dose Vitamin C​

The debate:

  • Linus Pauling promoted mega-doses (grams per day)
  • Most research shows benefits plateau around 200-400 mg/day
  • IV vitamin C studied in cancer (as adjunct therapy)

Evidence:

  • Blood levels plateau around 200 mg/day intake
  • High oral doses cause GI upset and kidney stone risk in susceptible people
  • IV vitamin C is different (reaches much higher blood levels)

Practical stance: 200-500 mg/day from food and supplements is plenty for most people. Mega-dosing has limited evidence and potential downsides.

Should Everyone Take a Multivitamin?​

The debate:

  • Some argue it's cheap insurance
  • Others say it's money wasted (or even harmful—certain nutrients in excess)
  • Most studies show no mortality benefit

Evidence:

  • Large studies (Physicians' Health Study II) show modest benefits for cancer in men
  • No consistent mortality benefit in healthy adults
  • Poorly formulated multis may include problematic forms/doses

Practical stance: Targeted supplementation (D, B12, K2 as needed) is likely more effective than a multivitamin. If you want a multi, choose a quality brand with bioavailable forms.

❓ Common Questions

Should I take a multivitamin?​

Multivitamins provide "nutritional insurance" but are often poorly formulated—low doses, poor forms, too many fillers. Targeted supplementation (D3, K2, magnesium, omega-3s) based on your specific needs is generally more effective. If you take a multi, choose a quality brand with bioavailable forms.

Can vitamins replace a healthy diet?​

No. Whole foods provide thousands of beneficial compounds beyond vitamins—fiber, phytonutrients, antioxidants—that work synergistically. Supplements fill specific gaps; they don't replicate food.

Are synthetic vitamins as good as natural?​

For most vitamins, synthetic forms work well. Notable exceptions:

  • Vitamin E: Natural (d-alpha) is better retained than synthetic (dl-alpha)
  • Folate: Methylfolate may be superior to folic acid, especially for MTHFR variants
  • Vitamin D: D3 is more effective than D2

What's the best time to take vitamins?​

  • Fat-soluble vitamins (A, D, E, K): With a meal containing fat
  • B vitamins: Morning (can be energizing); with food to reduce nausea
  • Vitamin C: Any time; split doses if taking high amounts
  • Iron: Empty stomach for best absorption (or with vitamin C), away from calcium

Can I overdose on vitamins?​

Fat-soluble vitamins (A, D, E, K) can accumulate to toxic levels. Water-soluble vitamins are generally safer (excess excreted), but mega-doses of B6, niacin, or vitamin C can cause issues. Stick to recommended doses unless supervised.

✅ Quick Reference (click to expand)

The 13 Essential Vitamins at a Glance​

VitaminRDABest SourcesKey FunctionDeficiency Risk
A700-900 mcgLiver, sweet potato, carrotsVision, immunityLow in developing countries
D600-800 IUSun, fatty fish, fortifiedBones, immunityEpidemic (40%+)
E15 mgNuts, seeds, oilsAntioxidantRare
K90-120 mcgLeafy greens, nattoClotting, bonesRare (gut bacteria make some)
B11.1-1.2 mgPork, whole grainsEnergy metabolismAlcoholics
B21.1-1.3 mgDairy, eggs, meatEnergy metabolismLow
B314-16 mgPoultry, fish, peanutsNAD/NADPRare (pellagra)
B55 mgWidespreadCoAVery rare
B61.3-1.7 mgPoultry, fish, potatoesProtein metabolismElderly, alcoholics
B730 mcgEggs, nuts, liverMetabolismVery rare
B9400 mcgLegumes, leafy greensDNA synthesisPregnant women
B122.4 mcgAnimal foods onlyNerves, DNAVegans, elderly
C75-90 mgCitrus, peppers, broccoliCollagen, immunitySmokers, poor diet

Supplement Forms to Prefer​

VitaminPreferred FormAvoid
DD3 (cholecalciferol)D2 (less effective)
Ed-alpha-tocopherol (natural)dl-alpha (synthetic)
KK2 MK-7 (for bone/heart)K1 alone (for clotting only)
B9Methylfolate (5-MTHF)Folic acid (for some people)
B12MethylcobalaminCyanocobalamin (less direct)

💡 Key Takeaways​

Essential Insights
  • 13 essential vitamins cannot be made by your body in adequate amounts—you must get them from food or supplements
  • Fat-soluble vitamins (A, D, E, K) are stored and can accumulate to toxic levels; water-soluble vitamins need regular intake
  • Vitamin D deficiency is epidemic — Test your levels and supplement if needed (most people need 1,000-4,000 IU D3)
  • B12 is only in animal foods — Vegans must supplement; elderly absorb it poorly
  • Folate vs folic acid: 40-50% of people have MTHFR variants; methylfolate may be preferable
  • Vitamin K2 (MK-7) directs calcium to bones instead of arteries — consider supplementing with D3
  • Choline is overlooked but essential for brain function; eggs are an excellent source
  • Food first — Whole foods provide vitamins plus thousands of beneficial compounds supplements can't replicate
  • Form matters — Natural vitamin E, methylfolate, methylcobalamin, and D3 are generally preferable to synthetic alternatives
📚 Sources (click to expand)

General Vitamin Information:

Vitamin A:

  • Tanumihardjo SA. Vitamin A: biomarkers of nutrition for development. Am J Clin Nutr. 2011;94(2):658S-665S. DOI: 10.3945/ajcn.110.005777 — Tier A

Vitamin D:

  • Holick MF. Vitamin D deficiency. N Engl J Med. 2007;357(3):266-281. DOI: 10.1056/NEJMra070553 — Tier A

  • Cashman KD, et al. Vitamin D deficiency in Europe: pandemic? Am J Clin Nutr. 2016;103(4):1033-1044. DOI: 10.3945/ajcn.115.120873 — Tier A

Vitamin K:

  • Schurgers LJ, Vermeer C. Differential lipoprotein transport pathways of K-vitamins in healthy subjects. Biochim Biophys Acta. 2002;1570(1):27-32. DOI: 10.1016/s0304-4165(02)00147-2 — Tier A

B Vitamins & Methylation:

  • Scaglione F, Panzavolta G. Folate, folic acid and 5-methyltetrahydrofolate are not the same thing. Xenobiotica. 2014;44(5):480-488. DOI: 10.3109/00498254.2013.845705 — Tier A

  • Bailey RL, et al. Monitoring of vitamin B-12 nutritional status in the United States. Am J Clin Nutr. 2011;94(2):552S-561S. DOI: 10.3945/ajcn.110.004143 — Tier A

Choline:

BCMO1 Gene (Beta-Carotene Conversion):

  • Leung WC, et al. Two common single nucleotide polymorphisms in the gene encoding beta-carotene 15,15'-monoxygenase alter beta-carotene metabolism in female volunteers. FASEB J. 2009;23(4):1041-1053. DOI: 10.1096/fj.08-121962 — Tier A

See the Sources Library for complete references.

🔗 Related Topics​

For Mo

When coaching users on vitamins:

Assessment First​

Before making recommendations, understand:

  1. Diet pattern: Vegan/vegetarian? Eggs? Fatty fish? (B12 and D risk assessment)
  2. Age: Over 50? (B12 absorption declines)
  3. Sun exposure: Limited outdoor time? Dark skin? High latitude? (D deficiency risk)
  4. Medications: PPIs, metformin, statins? (Nutrient depletion)
  5. Gut health: Any digestive issues? (Absorption concerns)
  6. Goals: Energy? Immunity? Pregnancy planning? (Prioritization)

Priority Recommendations​

For almost everyone:

  • Recommend vitamin D testing and likely supplementation (2,000-4,000 IU D3)
  • Suggest D3 + K2 MK-7 combination if supplementing D

For vegans/vegetarians:

  • B12 supplementation is NON-NEGOTIABLE (emphasize irreversible nerve damage)
  • 1,000 mcg methylcobalamin daily
  • Also monitor D, iron, zinc, omega-3s

For those over 50:

  • Recommend B12 supplementation (absorption from food declines with age)
  • Vitamin D testing and supplementation
  • Consider more comprehensive testing if fatigue/cognitive issues

For women planning pregnancy:

  • Folate NOW (neural tube develops before most women know they're pregnant)
  • Methylfolate preferred over folic acid
  • Choline is critical but often missing from prenatals

Common Mistakes to Catch​

  1. Taking vitamins without fat: Fat-soluble vitamins (A, D, E, K) need dietary fat for absorption
  2. Folic acid for everyone: Some need methylfolate (MTHFR variants)
  3. Ignoring symptoms because labs are "normal": Optimal ≠ lab normal range
  4. Mega-dosing vitamin A (retinol): Toxicity risk, especially in pregnancy
  5. Relying on plant beta-carotene for vitamin A: Conversion varies greatly by genetics

Example Coaching Scenarios​

User: "I'm tired all the time but my doctor says my blood work is normal." Response: "Let's dig deeper. 'Normal' lab ranges are wide and don't always reflect optimal function. A few questions: What's your actual vitamin D level? (Aim for 40-60 ng/mL, not just 'above 20.') What's your B12? (500+ pg/mL is better than 'low normal' at 250.) Have you tested ferritin (iron stores)? Also, are you taking any medications like PPIs or metformin that can affect nutrient absorption?"

User: "I'm vegan. What vitamins do I need?" Response: "The most critical is B12—you absolutely must supplement this. There are no reliable plant sources, and deficiency causes irreversible nerve damage. Take 1,000 mcg of methylcobalamin daily. You'll also want vitamin D3 (vegan versions from lichen exist), and monitor your iron and zinc levels since plant-based sources have lower bioavailability. Consider an algae-based omega-3 for DHA/EPA as well."

User: "Should I just take a multivitamin?" Response: "Multivitamins are often poorly formulated—wrong forms, low doses, and too many fillers. Targeted supplementation based on your specific situation usually works better. For most people, that means: vitamin D3 (get tested first), maybe K2 with it, and B12 if you're vegan, vegetarian, or over 50. What's your current diet like? That'll help us identify if you have any specific gaps."

Red Flags to Address​

  • Vegan not supplementing B12: This is dangerous—escalate urgency
  • High-dose retinol supplements: Toxicity risk, especially in pregnancy
  • Multiple symptoms pointing to one vitamin: Recommend testing before assuming
  • Taking vitamins on empty stomach: Fat-soluble vitamins need fat
  • "I eat healthy so I don't need supplements": D deficiency affects 40%+ regardless of diet
  • Pregnant/planning without folate: Neural tube defects are preventable