Vitamin B12: Why It Matters More as You Change Your Diet or Age

What Vitamin B12 Actually Does in the Body

Vitamin B12 works quietly behind the scenes on several fundamental processes. Its most well-known roles include:

• Red blood cell formation: B12 helps the bone marrow produce mature red blood cells that carry oxygen efficiently. Without adequate B12, cells can become abnormally large and poorly functioning — a condition called megaloblastic anemia.
• Nervous system maintenance: B12 is critical for producing myelin, the protective sheath that surrounds nerve fibers and allows signals to travel correctly between the brain and the rest of the body.
• DNA synthesis: Every time cells divide, they need B12 to replicate genetic material accurately.

Because B12 is stored in the liver, the body can draw on reserves for a period of time — but this also means deficiency can develop slowly and go unnoticed until reserves are significantly depleted.

Who Is at Greater Risk of Low B12 Status

B12 deficiency is not randomly distributed. Certain groups have consistently higher rates of inadequate intake or absorption:

People Following Plant-Based Diets

B12 occurs naturally almost exclusively in animal-derived foods — meat, fish, dairy, and eggs. People who reduce or eliminate these foods face a meaningful gap that fortified foods and supplements must fill. This applies to vegans and strict vegetarians especially. As more adults shift toward plant-forward eating patterns, awareness of this gap is increasingly important. The broader nutritional changes that accompany dietary shifts across a lifetime are worth understanding in context.

Adults Over 50

Aging reduces stomach acid production, which is needed to release B12 from food proteins. This makes it harder for older adults to absorb B12 from meat and dairy, even when intake appears adequate. The NIH notes that this is precisely why older adults may benefit from fortified sources or supplements — forms of B12 that don't require the same digestive steps. For a broader look at how nutrient needs evolve over time, see how nutrient requirements shift across life stages.

People With Certain Digestive Conditions

Conditions that affect the stomach lining or small intestine — including pernicious anemia, Crohn's disease, and celiac disease — can impair intrinsic factor production or B12 absorption. Surgery on the stomach or intestines may also reduce absorption capacity.

People on Certain Long-Term Medications

Proton pump inhibitors (PPIs), commonly used for acid reflux, and metformin, used for type 2 diabetes, have both been associated with reduced B12 absorption over time. People on long-term courses of these medications should discuss B12 monitoring with their doctor.

Where B12 Comes From — and How to Maintain Adequate Intake

For people who eat animal products regularly, dietary B12 is generally accessible. Key natural sources include clams and other shellfish (among the richest sources), beef liver, fish such as salmon and tuna, poultry, eggs, and dairy products including milk and cheese.

For those who eat little or no animal food, options include:

• Fortified foods: Many plant milks, breakfast cereals, and nutritional yeast products are fortified with B12. Checking nutrition labels is important, as not all products in these categories are fortified.
• Dietary supplements: B12 is widely available as cyanocobalamin or methylcobalamin in oral tablet, sublingual (under-the-tongue), or liquid forms. A healthcare provider or registered dietitian can help determine whether supplementation is appropriate and in what form.

Men navigating dietary changes should note that B12 is among the micronutrients men most commonly fall short on, particularly as diets shift. Similarly, understanding how nutritional needs shift for men through their 30s and beyond can provide useful context.

This article is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider with questions about your health or nutritional needs.