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Ozempic Vitamin Deficiency: Vitamin D, B12, Iron, Protein

October 26, 2026 · 6 min read · By the Sharpy team
The short answer

Ozempic does not pull vitamins out of your body, but eating much less can leave you short. In a study of about 461,000 adults starting a GLP-1, 22.4% were diagnosed with a nutritional deficiency within a year, and vitamin D was the most common at 13.6%. A September 2026 study found the same pattern in teens, at 16.8%. The fix is mostly food quality and protein, plus asking your doctor whether to test vitamin D, B12 and iron. Sharpy helps by giving you one daily protein target so your smaller meals still count.

Can Ozempic cause a vitamin deficiency? Not directly, but it can set one up. Semaglutide is not known to block vitamins. It makes you eat much less, and less food means fewer vitamins and minerals. In the largest study so far, 22.4% of adults who started a GLP-1 were diagnosed with a nutritional deficiency within a year. Vitamin D was the most common. The good news: most of this can be caught with a blood test and prevented with better food choices.

The topic is back in the news this week, with NewsNation reporting on October 26, 2026 that experts warn Ozempic users may face protein and vitamin D shortfalls. Here is what the research actually shows, which nutrients to watch and what to ask your doctor.

What do the studies say about GLP-1 vitamin deficiency?

Three studies are behind most of the headlines. None proves the drugs cause deficiencies, but they all point the same way.

Study Who was studied What they found
Butsch et al., Obesity Pillars, 2025 461,382 adults newly prescribed a GLP-1 (2017 to 2021), mostly with type 2 diabetes 12.7% had a deficiency diagnosed within 6 months, 22.4% within 12 months. Vitamin D was most common: 7.5% at 6 months, 13.6% at 12 months
Kerr, Ryder et al., Childhood Obesity, September 2026 2,031 GLP-1 users aged 10 to 17 16.8% had a deficiency diagnosis within a year. Vitamin D was most common at 12.4%. Only 5% got nutrition counseling in the first 30 days
Johnson et al., Frontiers in Nutrition, 2025 69 adults on a GLP-1 who kept a 3-day food record Below recommended intake for fiber, calcium, iron, magnesium, potassium, vitamins A, C, D and E. Protein was below needs per kilogram of body weight

A few things to keep in mind. The two big studies used insurance claims, so they count diagnoses, not blood levels. Some people may have had low vitamin D before they started. Abbott, which makes nutrition products, funded the adult study, and the teen study shares several of its authors. The food record study was small and run by GNC staff. Even so, the message is consistent: people on GLP-1s often eat too little of the good stuff, and few get nutrition help. If your appetite is so low that whole meals go missing, our guide to not eating enough on Ozempic covers the warning signs and a small-meal plan.

Which nutrients run low on Ozempic and other GLP-1s?

This table lists the nutrients that show up most in the research and in the 2025 joint advisory from four obesity and nutrition groups. The daily amounts are the general adult targets from the NIH Office of Dietary Supplements.

Nutrient Why it matters on a GLP-1 Adult daily target (NIH) Easy food sources
Vitamin D Bones and muscle; the most common deficiency in both big studies 600 IU (15 mcg); 800 IU over age 70 Salmon, trout, fortified milk, eggs
Vitamin B12 Nerves and red blood cells; metformin can lower it 2.4 mcg Fish, meat, eggs, dairy, fortified cereal
Iron Energy and oxygen in the blood 8 mg (men, women over 50); 18 mg (women 19 to 50) Lean beef, lentils, beans, spinach
Calcium Bone loss is a known risk during fast weight loss 1,000 to 1,200 mg Greek yogurt, milk, cheese, tofu made with calcium
Protein Protects muscle while you lose weight See our protein target guide Chicken, fish, eggs, cottage cheese, protein shakes
Fiber Helps with constipation, a common GLP-1 side effect 25 to 34 g (varies by age and sex) Beans, oats, berries, vegetables

Does Ozempic deplete vitamin B12?

There is no good evidence that semaglutide itself lowers B12. But many people who take Ozempic for type 2 diabetes also take metformin, and the metformin label says it can lower B12 levels and advises checking them. If you take both, ask your doctor when your B12 was last tested. People who eat little meat, fish, eggs or dairy are also at higher risk.

If you eat vegan, plant foods have no B12 unless it is added, so fortified foods or a supplement matter even more; our vegan GLP-1 guide covers B12 and protein on a plant diet.

What about vitamin B1 (thiamine)? Thiamine stores are small, so long stretches of vomiting or eating almost nothing can drain them. Doctors have reported rare cases in people on GLP-1s with severe, ongoing vomiting. If you cannot keep food down for days, call your doctor. Do not wait it out.

What about protein?

Protein is not a vitamin, but it is the shortfall that matters most for how you look and feel. When you lose weight fast, part of it can come from muscle. Eating too little protein makes that worse. The joint advisory lists "adequate protein intake and strength training to preserve lean mass" as one of its eight priorities.

This is the part you can fix yourself, every day. Sharpy gives you one protein target, a 20-minute workout and a Shape Score, so you can see your smaller meals are still feeding your muscles. For meal ideas, see our GLP-1 grocery list and 7-day GLP-1 meal plan.

What are the signs of a deficiency on a GLP-1?

Many signs overlap with normal side effects, which is why a test is better than guessing.

  • Tired all the time, even after the first few weeks. See our guide to fatigue on GLP-1.
  • Hair shedding or brittle nails. These have many causes. Our hair loss and Ozempic nails guides cover them.
  • Pale skin or getting out of breath easily, which can point to low iron or B12.
  • Tingling or numbness in the hands or feet, which can point to low B12.
  • Muscle weakness or bone aches, which can point to low vitamin D or too little protein.

How to lower your risk: a simple checklist

  1. Ask for a baseline check. The joint advisory recommends a nutrition assessment when you start a GLP-1. Ask your doctor whether to test vitamin D, B12, iron and a basic blood count.
  2. Eat protein first. Start each meal with the protein, then vegetables, then starch. Small appetite? This order matters most.
  3. Pick foods that pull double duty. Salmon (protein, vitamin D, B12), Greek yogurt (protein, calcium), eggs (protein, B12, vitamin D), lentils (protein, iron, fiber).
  4. Do not live on shakes and crackers. They are fine on bad days, but whole foods carry vitamins that snack foods do not.
  5. Talk to your prescriber before supplements. A basic multivitamin is common, but high doses of vitamin D or iron are not harmless. Be careful with products sold as "GLP-1 supplements," which we cover here.
  6. Recheck if symptoms show up. Do not stop or change your GLP-1 dose on your own. Talk to your prescriber.

If you are pregnant, under 18, or have a history of an eating disorder, your nutrition needs are different. Work with your doctor and a dietitian.

The bottom line

Ozempic vitamin deficiency is real but mostly preventable. The drug does not steal vitamins; eating much less does. About 1 in 5 adults starting a GLP-1 gets a deficiency diagnosis within a year, most often vitamin D. Ask about a baseline blood test, put protein and nutrient-dense foods first, and check with your doctor before taking supplements. To keep your daily protein on track and protect muscle while you lose fat, try Sharpy.

Sources

Questions people ask

Does Ozempic cause vitamin deficiency?

Not directly, as far as we know. The Ozempic label does not list vitamin deficiency as a side effect. But GLP-1 drugs cut appetite a lot, and when you eat less food you also get fewer vitamins and minerals. A large claims study found that 22.4% of adults starting a GLP-1 got a deficiency diagnosis within 12 months. It could not prove the drug caused it.

Can Ozempic cause vitamin D deficiency?

Vitamin D was the most common deficiency in both big studies. In adults, 13.6% were diagnosed with low vitamin D within a year of starting a GLP-1. In children and teens, it was 12.4%. Many people with obesity already have low vitamin D, so some of these cases may have been there before. Ask your doctor whether a blood test makes sense for you.

Does Ozempic deplete vitamin B12?

There is no good evidence that semaglutide itself lowers B12. Metformin is a different story: its label warns it can lower B12 levels. Many people with type 2 diabetes take both drugs, so B12 is worth asking about if you take metformin too.

Can I take vitamin D3 with Ozempic?

There is no known interaction between vitamin D3 and semaglutide in the Ozempic label. Still, the right dose depends on your blood level and health, so ask your doctor or pharmacist before starting a supplement, especially a high-dose one.

What vitamins should I take on a GLP-1?

There is no official vitamin list for GLP-1 users. A 2025 joint advisory from four obesity and nutrition groups says preventing micronutrient deficiencies is a priority and recommends a nutrition check at the start. Many doctors suggest a basic multivitamin when intake is very low, but that is a decision for you and your prescriber.

What are the signs of a nutrient deficiency on Ozempic?

Common signs are tiredness that does not go away, weakness, hair shedding, brittle nails, pale skin, shortness of breath on stairs, and tingling in the hands or feet. These overlap with normal GLP-1 side effects, so a blood test is the only way to know. Call your doctor if they last or get worse.

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