GLP-1 Vitamin Deficiencies: The 7 Nutrients Youre Probably Missing

May 24, 2026

GLP-1 Vitamin Deficiencies: The 7 Nutrients You're Probably Missing

By Dr. Onikepe Adegbola, MD PhD — Johns Hopkins-trained physician-scientist and founder of Casa de Sante

Key Takeaways

GLP-1 medications reduce food intake by 30-40%. This means 30-40% less of every vitamin and mineral that food provides. Nutritional deficiencies are not a possibility — they are a near-certainty without intervention.
The deficiencies develop slowly and insidiously. By the time symptoms appear (fatigue, hair loss, muscle weakness, mood changes), the deficit has been building for months.
Blood tests catch deficiencies early. Consider baseline labs before starting GLP-1 and monitoring every 6 months: CBC, iron panel, B12, folate, vitamin D, magnesium, zinc.

1. Vitamin D

Why it drops: Primary dietary sources (fatty fish, fortified dairy, eggs) are reduced. Less food = less vitamin D. Additionally, vitamin D is fat-soluble — reduced dietary fat impairs absorption.
Symptoms: Fatigue, bone pain, muscle weakness, frequent infections, depression.
Risk: Accelerated bone loss (already a concern on GLP-1 due to weight loss). Impaired immune function.
Solution: Test 25-OH vitamin D. Target 40-60 ng/mL. Supplement 2000-5000 IU daily with a fat-containing meal.

2. Iron

Why it drops: Major dietary sources (red meat, poultry, beans) are eaten in smaller quantities. GLP-1 can also reduce stomach acid production → impaired iron absorption (iron requires acid for conversion to absorbable form).
Symptoms: Fatigue (the most common symptom attributed to "just losing weight" but actually anemia), pale skin, cold hands/feet, brittle nails, hair loss, restless legs.
Risk: Women on GLP-1 + menstruation are at highest risk. Iron deficiency anemia can cause heart palpitations and exercise intolerance.
Solution: Test ferritin (storage iron) and CBC. Supplement if ferritin below 30. Take with vitamin C to enhance absorption. Take on an empty stomach if tolerated.

3. Vitamin B12

Why it drops: B12 requires stomach acid and intrinsic factor for absorption. GLP-1's effects on gastric function can impair both pathways. Reduced meat intake also reduces dietary B12.
Symptoms: Fatigue, brain fog, numbness/tingling in hands and feet, memory problems, balance issues, mood changes.
Risk: B12 deficiency causes irreversible nerve damage if left untreated. Patients on metformin + GLP-1 are at especially high risk (metformin also depletes B12).
Solution: Test serum B12 and methylmalonic acid (more sensitive). Supplement sublingual B12 1000mcg daily or B12 injections if severely deficient.

4. Magnesium

Why it drops: Found in nuts, seeds, leafy greens, whole grains — foods consumed in smaller quantities on GLP-1. Also lost in diarrhea (a GLP-1 side effect for some).
Symptoms: Muscle cramps, insomnia, anxiety, constipation, headaches, irregular heartbeat.
Risk: Magnesium is needed for 300+ enzymatic reactions. Deficiency affects bone health, cardiovascular function, blood sugar regulation, and mood.
Solution: Supplement 200-400mg glycinate (best absorbed, won't cause diarrhea) at bedtime. Also helps sleep quality.

5. Zinc

Why it drops: Red meat, shellfish, and legumes are primary sources — all typically reduced on GLP-1. Zinc absorption is also impaired by reduced stomach acid.
Symptoms: Hair loss (very common complaint on GLP-1 — often attributed to weight loss but may be zinc deficiency), impaired taste, slow wound healing, frequent infections, skin issues.
Risk: Hair loss on GLP-1 is multifactorial, but zinc deficiency is a correctable cause. Testing is inexpensive.
Solution: Test serum zinc. Supplement 15-30mg daily with food (zinc on empty stomach causes nausea).

6. Folate

Why it drops: Green leafy vegetables, legumes, and fortified grains are primary sources. Reduced intake → reduced folate.
Symptoms: Fatigue, mouth sores, mood changes, cognitive issues. In combination with B12 deficiency, can cause megaloblastic anemia.
Risk: Critical for women of childbearing age (neural tube defects). Important for DNA synthesis and repair.
Solution: Supplement methylfolate (the active form) 400-800mcg daily.

7. Calcium

Why it drops: Dairy products (major calcium source) are often reduced due to appetite suppression. Lactose-intolerant patients on GLP-1 may avoid dairy entirely.
Symptoms: Often silent until bone fracture occurs. Muscle cramps, numbness/tingling, and dental problems in severe deficiency.
Risk: Combined with weight-loss-related bone loss, calcium deficiency accelerates osteoporosis.
Solution: 1000-1200mg daily from food + supplements. Take in divided doses (500mg max per dose). Calcium citrate is better absorbed than calcium carbonate.

Monitoring Schedule

Test	Baseline	6 Months	12 Months	Annually
CBC + Iron Panel	✓	✓	✓	✓
Vitamin D (25-OH)	✓	✓	✓	✓
B12 + Folate	✓	✓	✓	✓
Magnesium	✓		✓	✓
Zinc	✓ (if hair loss)
DEXA (Bone Density)	✓ (if risk factors)		✓

🛒 GLP-1 Nutritional Insurance

Daily Vitamin — Specifically formulated to address the nutritional gaps created by reduced food intake on GLP-1. Contains therapeutic doses of vitamin D, B12, iron, magnesium, zinc, folate, and calcium — all 7 deficiency risks covered in one supplement. This is the single most important non-protein supplement on GLP-1.
Whey Protein — Protein deficiency is the 8th gap: not a vitamin, but the macronutrient most critically lacking on GLP-1. Protein is needed for iron transport (transferrin), B12 transport (transcobalamin), and calcium incorporation into bone (collagen). Without adequate protein, even perfect vitamin supplementation can't prevent complications.
Collagen Peptides — Provides glycine and proline for bone matrix formation (where calcium is deposited) and gut barrier repair (where nutrients are absorbed). If your gut barrier is compromised, you can't absorb the vitamins you're supplementing. Collagen fixes the absorption apparatus.

Medical Disclaimer: This article is for educational purposes only. Discuss lab monitoring with your prescribing physician. Self-treating suspected deficiencies without testing can mask serious conditions. Over-supplementation of certain nutrients (iron, vitamin A) can be harmful. Test, then treat. Dr. Adegbola is the founder of Casa de Sante.

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