How B12 Absorption Actually Works
When you eat a B12-rich food, the vitamin doesn’t simply pass into your bloodstream. It goes through a multi-step process:
1 – Stomach acid releases B12 from the food protein it’s attached to.
2 – B12 binds to a protein called intrinsic factor, produced by cells in the stomach lining.
3 – This travels to the end of the small intestine, where it is absorbed into the bloodstream.
4 – B12 is sent through the bloodstream to anywhere the body needs.
5 – If it gets sent to the brain, it must cross the blood brain barrier (we’ll cover that below).
If anything disrupts this chain – low stomach acid, insufficient intrinsic factor, or a damaged small intestine – B12 absorption drops significantly, even if you’re eating plenty of B12-rich foods. This is why B12 deficiency can occur even if you eat enough.
What gets in the way of B12 absorption
Low Stomach Acid – Stomach acid is essential for releasing B12 from food in the first place. Several common factors reduce stomach acid production:
- Chronic stress
- Proton pump inhibitors (PPIs) and antacids
- Eating too quickly or in a rushed, distracted state
- Age: stomach acid production tends to decline over time
If you have a dysregulated nervous system, you’re likely not absorbing B12 well. This is why I always recommend people start with my guides to nervous system regulation and interoception with ADHD before following the ADHD diet. To learn more, visit my store here.
Gut Inflammation or Damage – The small intestine is where B12 is absorbed, and any inflammation or damage to its lining reduces absorptive capacity. Conditions like coeliac disease, Crohn’s disease, or general gut dysbiosis can all impair B12 uptake.
Certain Medications – Certain medications are well documented to affect B12 levels. These include:
- Metformin
- Some antacids and PPIs (proton pump inhibitors, if used more than 8 weeks in a row typically)
- Oral birth control (women)
Restrictive or selective eating – Many people with ADHD are selective eaters. Whether it’s sensory sensitivities, impulsivity, hyper-palatable food cravings, or random food intolerance at mealtimes can significantly narrow the range of nutrients.
Continued below…
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How to Support Better B12 Absorption
Chew Thoroughly and Eat Without Rushing
Digestion begins in the mouth, and proper chewing signals the stomach to produce acid and enzymes. Eating in a calm, seated, unhurried environment makes a genuine difference to digestive function. If that’s difficult, taking a short walk or movement after may help. Even a ritual like 3 deep breaths, dimmer lights to reduce sensory overload, or a prayer before a meal is better than nothing.
Include Zinc-Rich Foods
Zinc is needed for the production of stomach acid and digestive enzymes. Good food sources include pumpkin seeds, meat, eggs, and legumes. Zinc deficiency is also common in children with ADHD, making zinc-rich foods a double win.
Address Gut Health if Needed
If you have frequent digestive symptoms — bloating, reflux, loose stools, constipation, or stomach pain — alongside ADHD, it is worth investigating gut health with a healthcare provider. Poor gut integrity can impair B12 absorption.
Practice Nervous System Regulation Skills
Anything counts: listening to your body when it needs to use the bathroom, taking deep breaths, taking a break every hour, going outside. The goal is to teach your body that it’s safe. The unfortunate truth is that it is a long process that takes daily practice. But remember: something is always better than nothing. And something one day and nothing another is better than nothing all week.
Foods Highest in B12
B12 is found almost exclusively in animal products. If you don’t use animal products, it’s also found in nutritional yeast. Here are the best dietary sources, roughly ordered by B12 content:
Richest sources:
- Clams and oysters
- Beef liver
- Salmon and trout
- Sardines and tuna
- Beef and lamb
Good everyday sources:
- Eggs
- Milk and yogurt
- Cheese
- Chicken and turkey
For Plant-Based or Restricted Diets:
- Nutritional yeast
- Fortified plant milks
- Fortified breakfast cereals
Final Thoughts
At the end of the day, remember optimizing your nutrient absorption is a high level executive function. You can usually enhance your absorption simply by following these three guidelines:
- Practice nervous system regulation and interoception
- Eat plenty of protein
- Eat plenty of plants
Do that, and usually the rest will follow once you have the energy to focus on higher level functions.
This article summarizes the research from the linked studies and the author’s knowledge. It is for educational purposes only. Nothing in this article constitutes medical advice.
