Can Vitamin B12 Cause Acid Reflux? Eye-opening Studies

As I explain in my Q&A on Vitamin B Deficiency and Acid Reflux Vitamins Guide, B12 absorption depends on having enough stomach acid. But many people with reflux are dealing with low stomach acid—often due to acid-blocking medications, H. pylori infection, chronic stress, nutrient deficiencies, aging, or other underlying issues.

A study published in the National Library of Medicine highlights that low stomach acid—no matter the cause—can interfere with digestion and nutrient absorption. This includes key micronutrients like calcium, iron, folic acid, vitamin B6, and, of course, vitamin B12.

And here’s something most people don’t realize: certain vitamins can directly trigger reflux. I took a daily multivitamin for years without realizing it was making my symptoms worse. After eliminating obvious triggers, I finally noticed that even my vitamins were contributing—just in a more subtle way.

For example, my gummy multivitamin contained added sugar, a well-known reflux trigger. My fish oil supplement also made my symptoms worse. The sugar, synthetic ingredients, and even the fat in the fish oil were hard on my compromised digestion.
It was a wake-up call. The very vitamins I was taking to support my health were actually making my symptoms worse. That’s when I started looking more closely at ingredient labels and paying attention to how different forms of vitamins affected my digestion.

For most people, oral B12 is easy on the stomach—as long as you’re taking the right kind. Some supplements sneak in added sugar, artificial sweeteners, or synthetic fillers that can irritate digestion, especially if you’re already dealing with reflux. If that’s you, choosing a cleaner option can make a big difference while you work on getting your gut back on track.

But the injected form is a different story. Some people feel great on B12 shots, while others experience nausea, diarrhea, or other digestive discomforts. The nasal spray isn’t always trouble-free either—it can sometimes bring on nausea as well. If you’re reacting to a supplement or treatment, it doesn’t necessarily mean B12 isn’t right for you—it just might mean you need to find a better delivery method.

Absolutely. B12 is essential for nerve function, including the nerves that control digestion. When levels are low, digestion can slow down, leading to constipation. On the flip side, some people experience the opposite problem—food moving too quickly through the intestines, causing diarrhea.

If you’ve been struggling with irregular bowel movements and haven’t considered B12 as a factor, it’s worth checking your levels. Getting enough B12 can help keep digestion running smoothly and support a healthier gut over time.

B12 itself doesn’t cause gas and bloating, but a deficiency can set the stage for digestive discomfort. Since B12 helps regulate nerve function in the gut, low levels can slow digestion, allowing food to sit in the stomach longer and ferment—leading to gas and bloating.

If you’re taking B12 and still experiencing these symptoms, the real culprit might not be the vitamin itself but what’s in your supplement. Sugar, artificial sweeteners, and synthetic fillers can feed harmful bacteria in the gut, worsening bloating and even deepening reflux symptoms. Switching to a cleaner B12 supplement can be an easy fix that makes a big difference.