GLP-1 Vitamin Deficiencies: The 7 Nutrients You Are Most Likely Missing

May 24, 2026

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

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

Key Takeaways

Reduced food intake on GLP-1 → reduced nutrient intake → deficiencies develop over weeks to months. These aren't theoretical — they're measurable on bloodwork and cause real symptoms.
GLP-1 medications also impair ABSORPTION of certain nutrients: delayed gastric emptying → altered nutrient timing, and potential effects on intestinal absorption. Eating less AND absorbing less is a double hit.
The 7 most common deficiencies: vitamin B12, vitamin D, iron, zinc, magnesium, calcium, and omega-3 fatty acids. Each has specific symptoms and consequences.
Proactive supplementation is far better than waiting for deficiency symptoms to appear. Get baseline bloodwork before or early in GLP-1 treatment, then monitor every 3-6 months.

1. Vitamin B12

Why GLP-1 depletes it: B12 absorption requires stomach acid and intrinsic factor. GLP-1 delays gastric emptying and may alter the environment needed for B12 release from food. Combined with reduced meat intake (a primary B12 source), deficiency develops.
Symptoms: Fatigue, brain fog, numbness/tingling in hands and feet (peripheral neuropathy), depression, memory problems.
Testing: Serum B12 (normal >400 pg/mL) and methylmalonic acid (MMA — a more sensitive marker).
Solution: Methylcobalamin (the active form) 1000-2000mcg daily. Sublingual absorption bypasses the GI tract entirely.

2. Vitamin D

Why GLP-1 depletes it: Vitamin D is fat-soluble — requires dietary fat for absorption. Reduced food intake + reduced fat intake = reduced D absorption. Many patients were already deficient before starting GLP-1 (over 40% of Americans are vitamin D deficient).
Symptoms: Fatigue, muscle weakness, bone pain, depression, frequent illness, impaired wound healing.
Testing: 25-OH vitamin D. Target 40-60 ng/mL.
Solution: Vitamin D3 2000-5000 IU daily with food containing fat. Higher doses under physician supervision if severely deficient.

3. Iron

Why GLP-1 depletes it: Iron absorption requires stomach acid. Reduced meat intake compounds the problem. Menstruating women are at highest risk.
Symptoms: Fatigue (the most common cause of persistent tiredness on GLP-1 beyond expected caloric restriction), weakness, pale skin, hair loss, cold extremities, restless legs.
Testing: Ferritin (storage iron — target >50 ng/mL for optimal energy), serum iron, TIBC.
Solution: Ferrous sulfate 325mg every other day with vitamin C (enhances absorption). Daily dosing is poorly absorbed and causes more GI side effects — alternate-day dosing is equally effective with better tolerance.

4. Zinc

Why GLP-1 depletes it: Zinc comes primarily from meat, shellfish, and seeds. Reduced food intake → reduced zinc. Additionally, zinc absorption requires adequate stomach acid.
Symptoms: Impaired immune function (frequent colds), hair loss, altered taste (food tastes "off"), slow wound healing, skin problems.
Testing: Serum zinc (though not highly reliable — normal range doesn't exclude tissue deficiency).
Solution: Zinc glycinate 15-30mg daily. Take separately from iron (they compete for absorption).

5. Magnesium

Why GLP-1 depletes it: Magnesium is found in nuts, seeds, leafy greens, and whole grains — foods often under-consumed on GLP-1. Also depleted by stress and poor sleep (common during weight loss).
Symptoms: Muscle cramps, anxiety, insomnia, constipation (very common complaint on GLP-1 — magnesium deficiency may be contributing), headaches, heart palpitations.
Testing: Serum magnesium (only reflects 1% of body stores — RBC magnesium is more accurate but rarely ordered).
Solution: Magnesium glycinate 200-400mg at bedtime (also helps sleep and constipation). Magnesium citrate if constipation is the primary concern.

6. Calcium

Why GLP-1 depletes it: Calcium absorption requires stomach acid and vitamin D. Dairy reduction (common with nausea on GLP-1) removes the primary dietary source. Weight loss itself increases bone turnover.
Symptoms: Often silent until bone density loss is significant. Muscle cramps, dental problems, and numbness in later deficiency.
Testing: Serum calcium is NOT useful (maintained by bone release). DEXA scan after significant weight loss to assess bone density.
Solution: Calcium citrate 500-600mg twice daily (citrate doesn't require stomach acid for absorption — better than carbonate for GLP-1 patients). Always take with vitamin D.

7. Omega-3 Fatty Acids (DHA/EPA)

Why GLP-1 depletes it: Primary sources are fatty fish, walnuts, and flaxseeds. Reduced food intake + nausea-driven fat avoidance → insufficient omega-3. These are essential fats — the body cannot make them.
Symptoms: Dry skin, brittle nails, joint stiffness, brain fog, increased inflammation, worsened mood.
Testing: Omega-3 index (measures EPA+DHA in red blood cell membranes — target >8%).
Solution: Fish oil 1000-2000mg EPA+DHA daily. Take with food. Algae-based omega-3 for vegetarians.

The Monitoring Schedule

Baseline (before starting GLP-1): CBC, CMP, B12, vitamin D, ferritin, magnesium, zinc.
3 months: Recheck ferritin, B12, vitamin D (the fastest to become deficient).
6 months: Full panel repeat. Adjust supplementation based on results.
12 months: Full panel + consider DEXA scan for bone density.
Annually thereafter.

🛒 Complete GLP-1 Nutritional Support

Daily Vitamin — Formulated by a physician specifically for the nutritional gaps that GLP-1 creates: bioavailable B12, vitamin D3, iron bisglycinate, zinc, magnesium, calcium, and the full spectrum of micronutrients most commonly depleted during significant weight loss. One supplement covers 6 of the 7 deficiency categories. This isn't optional on GLP-1 — it's essential preventive care.
Whey Protein — Protein is the vehicle for many micronutrients. Whey naturally contains calcium, B vitamins, and zinc. Each shake contributes to your protein target AND your micronutrient needs. When eating less, every calorie must do double duty — whey protein delivers both.
Collagen Peptides — Provides glycine, which is used for glutathione production (the body's master antioxidant). During weight loss, oxidative stress increases as stored toxins are released from fat cells. Adequate glycine supports the detoxification pathways that process these released compounds.

Medical Disclaimer: This article is for educational purposes only. Do not megadose vitamins without medical supervision. Iron supplementation should be based on bloodwork (excess iron is harmful). If you experience neurological symptoms (numbness, tingling, balance problems), get B12 tested urgently — untreated B12 deficiency can cause permanent nerve damage. Dr. Adegbola is the founder of Casa de Sante.

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