Nutrient Gaps on Ozempic and Wegovy: Why GLP-1 Users Need B12 and Vitamin D
GLP-1 vitamin deficiency isn't a rare side note buried in a drug insert. It's showing up often enough in real-world data that obesity medicine researchers are now calling it a predictable consequence of how these medications work, not an occasional complication.
A 2025 study in Obesity Pillars tracked more than 460,000 adults starting GLP-1 receptor agonists like semaglutide (Ozempic, Wegovy) and tirzepatide (Mounjaro, Zepbound) and found that 12.7 percent developed a diagnosed nutritional deficiency within six months of starting treatment, and 22.4 percent had one within a year. Vitamin D deficiency was the most common finding, affecting 13.6 percent of users at the one-year mark.
Why This Happens
GLP-1 medications don't cause malabsorption the way bariatric surgery can. The mechanism is simpler and, in a way, more obvious once you see it: these drugs slow gastric emptying and suppress appetite, so people eat meaningfully less food overall, including less of the food that would otherwise supply vitamin D, B12, iron, and calcium.
A 2025 dietary-intake study in Frontiers in Nutrition put numbers on exactly how far short people fall. Among GLP-1 users studied, 98.6 percent were not meeting recommended vitamin D intake through diet, and most participants also fell short on magnesium, iron, potassium, and several other nutrients. A separate diet-record study summarized by Harvard Health found 72 percent of GLP-1 users weren't getting enough calcium and 64 percent weren't getting enough iron, with only 1.4 percent meeting vitamin D recommendations.
B12 is a slightly different story. Researchers haven't identified a direct pharmacological link between GLP-1 drugs and B12 absorption, but a 2025 obesity medicine commentary in the International Journal of Obesity points to several indirect mechanisms: reduced dietary variety, less intake of B12-rich foods like meat and dairy, and in some patients, interaction with metformin, which is independently known to lower B12 levels over time.
What Obesity Medicine Researchers Are Recommending
Formal clinical guidelines are still catching up to how fast GLP-1 prescriptions have grown, but the 2025 International Journal of Obesity commentary lays out an interim approach that's becoming common in practice:
- Baseline nutritional assessment before or shortly after starting treatment, including bloodwork for at-risk patients
- A daily multivitamin and mineral supplement containing iron, zinc, copper, B12, and folic acid as a pragmatic default while formal screening protocols develop
- Ongoing monitoring for patients who are older, menstruating, or already following a restrictive diet
- Referral to a registered dietitian for patients managing significant appetite suppression
That last point matters because appetite suppression doesn't just reduce meals. It also makes swallowing a handful of pills, on top of an already-reduced food intake, feel like one more unwanted task on a day when eating anything already feels effortful.
The Nausea Problem Nobody Talks About
Nausea, early fullness, and general GI discomfort are some of the most common side effects of GLP-1 therapy. For patients dealing with those symptoms, a large multivitamin tablet is genuinely harder to get down, and some people skip the supplement entirely on their worst days, which is exactly when they can least afford to.
Bariatric nutrition practice, which obesity medicine researchers now draw on directly for GLP-1 patients, has dealt with this exact problem for years. The common workaround is switching to formats that don't require swallowing a pill: chewables, liquids, or, in B12's case, sublingual delivery that dissolves under or on the tongue instead of needing to go down.
This is where Calmour's Vitamin B12 strips and Vitamin D3 strips fit into a GLP-1 routine. Both dissolve on the tongue in under 30 seconds with no water and nothing to swallow, which matters on a day when nausea is already working against you. Talk to your doctor about which nutrients to monitor and supplement, since GLP-1 treatment plans and existing conditions vary enough that a one-size answer doesn't apply.
What to Actually Ask Your Doctor
Bring up baseline labs for vitamin D and B12 when you start a GLP-1 medication, not six months in when a deficiency has already developed. If you're already several months into treatment and haven't had labs checked, that's a reasonable thing to ask for at your next appointment, especially if you've noticed fatigue, which is a symptom both deficiencies share and one that's easy to write off as just part of the medication.
FAQ
Do GLP-1 medications directly cause vitamin deficiencies?
Not through malabsorption. The mechanism is reduced food intake. Appetite suppression and slower gastric emptying mean less overall nutrient intake, which is why vitamin D and B12 gaps are common findings in GLP-1 users specifically.
How common is vitamin D deficiency in GLP-1 users?
A 2025 claims analysis of over 460,000 GLP-1 users found 13.6 percent had a diagnosed vitamin D deficiency within 12 months of starting treatment, making it the most frequently diagnosed nutrient gap in that population.
Should everyone on Ozempic or Wegovy take a B12 supplement?
There's no universal answer yet since formal guidelines are still developing. Obesity medicine researchers currently recommend baseline nutrient assessment and, often, a daily multivitamin containing B12 as a pragmatic interim approach. Talk to your doctor about your specific situation.
Why would a sublingual or dissolving strip work better than a pill for GLP-1 users?
GLP-1 medications commonly cause nausea and early fullness. A dissolving format that doesn't require swallowing can be easier to tolerate on days when even a small pill feels like too much.
The Takeaway
GLP-1 medications are doing exactly what they're designed to do when appetite drops. The nutrient gaps that can follow are a predictable side effect of that mechanism, not a personal failure to eat well enough. Baseline labs, a conversation with your doctor, and a supplement routine that doesn't fight against nausea are the three pieces that actually address it.
Ready to close the gap? Shop Calmour's Vitamin B12 strips and Vitamin D3 strips. Learn more about the strip format on the Calmour Difference page, or browse the full lineup at Calmour's collection page. For more on B12 specifically, see 12 warning signs of vitamin B12 deficiency.
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. Consult your doctor before starting any new supplement, especially if you are taking prescription medication.
