Vitamin B12 is a nutrient that is needed for DNA synthesis, the formation of red blood cells, the functioning of the nervous system, normal growth and cell reproduction, and fish, dairy, and other animal products. In most cases, stomach acid and intrinsic factor are required for the binding and absorption of vitamin B12. However, when absorption is impaired, both oral and sublingual supplementation forms can be effective.
How Absorption Works
Oral capsule vitamin B₁₂ supplementation absorption involves two main mechanisms. First, active absorption depends on an intrinsic factor (IF), which is a glycoprotein made in the stomach. Once in the small intestine, Vitamin B₁₂ binds to IF, forming a complex that is recognized by receptors on the intestinal walls and then absorbed into the bloodstream. This pathway is efficient but saturable. Second, passive diffusion occurs when very high oral doses are consumed. A small percentage, around 1–2% of the dose, is absorbed passively across the gut lining without IF. This makes it possible for oral megadoses—such as 1,000 mg or more per day—to raise serum B12 levels even in people who have severe anemia or low stomach acid. Sublingual supplementation bypasses much of the digestive system. Tablets or lozenges are placed under the tongue and dissolve, allowing some vitamin B₁₂ to be absorbed directly through the oral mucosa into the bloodstream.
Vitamin B₁₂ absorption depends on the dose and route. At normal dietary levels (1–2 mcg), absorption relies on intrinsic factor and maxes out around 1.5–2 mcg per meal. At higher supplement doses (500–2000 mcg), only about 1–2% is absorbed passively, but this is still effective for treating a deficiency. Sublingual B₁₂ is often marketed as superior, but studies show it offers no significant absorption advantage over oral capsules, as both raise serum B12 levels similarly.
When It Is Hard to Take in Information In conditions like pernicious anemia or post-gastric surgery, intrinsic factor is insufficient. While intramuscular injections remain the gold standard, high-dose oral supplementation (≥1,000 µg daily) shows promising efficacy comparable to injections in many cases. Due to the potential bypass of the digestive tract, individuals with these issues frequently favor sublingual forms. Certain populations are at higher risk of vitamin B₁₂ deficiency and may benefit more from supplementation, regardless of their dietary intake. Older adults, for example, often experience conditions that affect their ability to absorb nutrients. For instance, atrophic gastritis reduces stomach acid necessary for releasing B₁₂ from food proteins. This makes them less able to absorb naturally occurring B₁₂, even if their diet includes animal products.
Additionally, individuals on long-term proton pump inhibitors (PPIs) or metformin therapy are at increased risk due to drug-related malabsorption. Lastly, vegetarians and vegans, who avoid animal products altogether, are also common candidates for B₁₂ supplementation.
When and How to Use Each Form Oral capsules work well for most adults with adequate stomach acid and intrinsic factor, especially when taking 1,000–2,000 µg daily.
Sublingual tablets may benefit individuals who have low stomach acid, pernicious anemia, gastrointestinal conditions, or difficulty swallowing pills.
Make sure to consult with your provider before taking any supplements! They will help guide you to make the best choice in terms of type and dosage.
Options for B12 Supplements Certified by NSF Choosing supplements that have been certified by a third-party ensures content safety, accuracy, and purity. The National Sanitation Foundation (NSF) grants its seal of approval when it determines that a product, its manufacturing process, and the manufacturing facility comply with its internal requirements. The following oral and sublingual B₁₂ supplements are some examples of NSF-certified for safety and label accuracy:
Oral Capsules: Naturewise Vitamin B12 1000mcg Softgels
Garden of Life Vitamin Code Raw B₁₂ Capsules
Thorne Vitamin B₁₂ capsules
Sublingual:
Pure TheraPro BioActive Vegan Methyl B₁₂ Sublingual Liquid
Perque Activated B‑12 Guard
Sublingual Methylcobalamin Solgar
Final Thoughts
Daily high-dose B12 supplements, whether taken orally or sublingually, can effectively restore levels in most people who are deficient, sometimes even in those whose B12 absorption is impaired. The evidence shows that any route of supplementation is effective, so use the therapy regimen that works best for you and your healthcare team. Always choose NSF-certified supplements to ensure purity and accuracy. If you have known absorption issues or medical conditions, work with a healthcare provider to determine the ideal route and dosage for your needs.
