Conditions
You’re taking supplements. You’re eating well. But your levels aren’t moving. Iron stays low. B12 stays low. Magnesium, zinc, calcium. The problem might not be what you’re putting in. It might be what your stomach isn’t doing.
Written by Michael D. Erdman, MBBS · Reviewed May 2026
Your iron is low. Your B12 won’t budge. Your doctor keeps increasing the dose and nothing changes. You’re taking everything right, but your body isn’t absorbing any of it. The problem might not be what you’re putting in. It might be what your stomach isn’t doing with it.
Your stomach acid isn’t just for digestion. It’s essential for unlocking nutrients from food and making them available for absorption. Iron needs an acidic environment to convert into a form your body can use. B12 requires acid to be released from the proteins it’s bound to in food. Calcium and magnesium absorption both depend on adequate stomach acidity.
But B12 absorption has a second layer. The parietal cells that produce hydrochloric acid also produce intrinsic factor, the specific transport protein that binds B12 in the small intestine and enables its absorption. When parietal cell function declines, both acid and intrinsic factor production fall. This means B12 absorption is impaired through two separate mechanisms: the acid-dependent release of B12 from food, and the intrinsic-factor-dependent uptake of B12 in the ileum. Oral B12 supplementation may not overcome a true intrinsic factor deficiency, which is why some patients require injections.
When acid is low, these nutrients pass through your digestive system without being properly absorbed. You can take high-dose supplements and still see no improvement. The bottleneck isn’t intake. It’s upstream, in the stomach.
People with persistent nutrient deficiencies despite adequate supplementation. Iron infusions that provide temporary relief but levels that drop again. B12 injections because oral supplements don’t absorb. Calcium supplementation that doesn’t prevent bone density decline.
In many of these cases, nobody has looked at stomach acid. The assumption is that if you take the nutrient, it absorbs. But absorption requires the right environment. If your stomach isn’t producing enough acid to create that environment, supplementation is working against a closed door.
The Heidelberg test measures your stomach acid in real time. For someone with persistent nutrient deficiencies, this answers a fundamental question: is your stomach creating the right environment for absorption?
If the test shows normal acid production, the malabsorption has a different cause. If it shows low acid, you and your practitioner have a clear starting point for addressing the root of the problem rather than endlessly supplementing around it.
If your nutrient levels aren’t responding to supplementation, a Heidelberg test can show whether your stomach acid is part of the equation. About an hour, no sedation, results the same day.
See if the Heidelberg test is your next step.