When you’re on a GLP-1 like semaglutide or tirzepatide, eating less is the point. The food noise quiets down. Portions shrink. For a lot of people, it’s the first time weight loss has felt possible.
But here’s a question that doesn’t come up often enough: if you’re eating less food, are you getting less of the vitamins and minerals your body needs too? A 2026 research review suggests it’s worth checking. This guide explains GLP-1 vitamin labs in plain English, and what options exist after you have your numbers.
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What the 2026 Research Found
In January 2026, the journal Clinical Obesity published a review of studies on nutrition in people taking GLP-1 medicines. The researchers looked at six studies covering more than 480,000 adults. Here’s what they reported:
- Vitamin D was the most common shortfall. About 7.5% had low vitamin D at 6 months, and 13.6% at 12 months.
- Iron levels tended to be lower. GLP-1 users had 26% to 30% lower ferritin, a measure of stored iron, than people on a different type of diabetes medicine.
- Intake was often low. More than 60% of users ate less calcium and iron than recommended.
- B vitamins, including B1 and B12, showed shortfalls that grew over time.
Now the honest part. These were mostly observational studies. That means they found patterns, but they can’t prove the medicine caused the low levels. The authors suggested “targeted nutritional assessment” for people at higher risk. In plain English: check, don’t guess.
Why Eating Less Can Mean Fewer Nutrients
This one is simple math. Vitamins and minerals come mostly from food. If you eat a third less food, you may get a third less of everything in it, unless you plan for it.
GLP-1 medicines may also slow how fast your stomach empties, and some people find certain foods harder to tolerate, like meat. Meat is a major source of iron and B12. Skip it often, and those numbers can slip.
Other things that raise your risk:
- Past weight loss surgery
- Eating little or no meat or dairy
- Taking metformin, which is linked to lower B12 in some people
- Taking acid-reducing medicines for a long time
- Heavy periods, which drain iron
5 GLP-1 Vitamin Labs Worth Asking About
These are common tests your doctor may consider. Your doctor decides which ones fit you.
- Vitamin D (25-hydroxy vitamin D). The most common shortfall in the 2026 review.
- Ferritin and iron studies. Ferritin shows your stored iron. A complete blood count shows if you’re anemic.
- Vitamin B12. Sometimes with extra tests if the result is borderline, since B12 tests can be tricky to read.
- A basic metabolic panel. This includes electrolytes and kidney function, which matters if you’ve had nausea or dehydration.
- Folate and other B vitamins, if your doctor thinks they fit.
A note about B12 tests
B12 results aren’t always simple. A published case report described a woman on semaglutide whose B12 looked low on a standard test, but more detailed tests showed it was actually normal. That’s why your doctor may want to confirm a low result before treating it. Don’t start high doses of anything based on one number alone.
What Your GLP-1 Vitamin Labs Can Tell You
Your results usually land in one of three places:
- Normal. Keep eating well and recheck when your doctor suggests.
- A little low. Often a food plan or an oral supplement is the first step.
- Clearly low. Your doctor may suggest a stronger option, like an injection or, for iron, an infusion, depending on the cause.
The key word is your. Your labs, your health, your plan. Not a one-size package.
How to Get Your Vitamin Labs Done
You have a few easy paths:
- Your primary care doctor. Ask at your next visit, or call to request the tests.
- Your weight loss prescriber. Many programs include check-ins where vitamin labs can be ordered.
- A recent physical. You may already have some results. Check your patient portal.
When you go, ask whether you need to fast. Most vitamin labs don’t require it, but some panels do.
How often to recheck
There’s no single schedule for everyone. Your doctor may suggest checking before you start a GLP-1, again after a few months, and then about once a year, or sooner if you feel run down. If you change your diet a lot, like cutting out meat, that’s a good reason to recheck GLP-1 vitamin labs sooner.
Bring your results to your visit
If you already have vitamin labs from the last few months, bring them. It saves time and helps your clinician make a clear plan without repeating tests you don’t need.
Options After Your GLP-1 Vitamin Labs
At our physician-led practice in Greenacres, these are options we may discuss, only if your clinician says they fit:
- B12 shot. Listed as an add-on on our IV drip menu.
- Vitamin D add-on. Also listed on the menu.
- Metabolism Support Drip. Fluids with B12, B-complex, and MIC (methionine, inositol, choline). It supports a weight plan. It doesn’t replace food, movement, or your medicine.
- Iron Infusion. Only for people whose blood work shows low iron, and only when labs and your clinician say it fits. Read more in our guide to low ferritin.
None of these are needed just because you take a GLP-1. They’re tools for real gaps, found with real labs.
Food comes first
Before any shot or drip, we’ll talk about food. Protein at every meal. Leafy greens and beans for folate and iron. Dairy or fortified foods for vitamin D and calcium. Small, steady meals work better than skipping and then eating big.
For Our Medical Weight Loss Patients
If you’re on our medical weight loss program, ask us about GLP-1 vitamin labs at your next check-in. If you’ve been feeling more tired than expected, tell us. Fatigue on a GLP-1 can come from eating too little, poor sleep, low iron, or dehydration. Our guides to semaglutide dehydration and IV therapy for energy cover more.
Frequently Asked Questions
Do GLP-1 medicines cause vitamin deficiencies?
Studies show patterns of lower vitamin D, iron, and some B vitamins in GLP-1 users, but they can’t prove the medicine is the cause. Eating less is a big factor. Lab checks help sort it out.
Which GLP-1 vitamin labs should I ask about?
Common ones include vitamin D, ferritin and iron studies, B12, and a basic metabolic panel. Your doctor decides which fit you.
Should everyone on semaglutide get B12 shots?
No. B12 shots make sense for people with a confirmed low level or a clear risk. Labs come first.
Can I just take a multivitamin?
For some people, a multivitamin plus a good food plan is enough. Ask your doctor, since some supplements interact with medicines.
Is an iron infusion common on a GLP-1?
Not routinely. An iron infusion is only for lab-confirmed low iron when your clinician says it fits.
Check, Don’t Guess
You’re doing the hard work of changing your health. Make sure your body has what it needs along the way. Book a visit, bring your recent labs if you have them, and we’ll walk through what makes sense for you.
Book a private consultation or call (561) 363-5538.
Majestic Aesthetics · 5315 Lake Worth Road, Greenacres, FL 33463 · (561) 363-5538
This article is general education, not medical advice. Individual results vary. Consultation required. Not all patients are candidates.
Want to keep reading? Find more plain-English guides on our blog, or start with our IV therapy overview.
Related reading: Semaglutide Nausea and Dehydration: When to Call Your Prescriber and When to Ask About IV Fluids · IV Therapy for Energy: What It May Help and What It Won’t · Tired All the Time? What the 2026 Ferritin Guidelines Mean for Women in Palm Beach County
