Nutrition & Supplements

Vitamin B12 Deficiency: Why It's More Common Than You Think

Vitamin B12 deficiency is one of the most common and most commonly missed nutrient deficiencies in adults — particularly in people over 40, vegetarians, those on metformin or acid-blocking medications, and anyone with gut absorption problems.

What B12 Actually Does

Vitamin B12 (cobalamin) is essential for:

• Red blood cell formation — deficiency causes megaloblastic anemia
• Neurological function — B12 is required for myelin sheath synthesis; without it, nerves degenerate
• DNA synthesis — required for cell division and tissue repair
• Methylation — B12 is a critical cofactor in the methylation cycle, affecting gene expression, detoxification, and neurotransmitter production
• Energy production — B12 supports mitochondrial function
• Mood regulation — B12 is required for serotonin and dopamine synthesis

Because B12 is involved in so many fundamental processes, deficiency produces a wide-ranging constellation of symptoms.

Symptoms of B12 Deficiency

• Fatigue and weakness — often severe and unexplained
• Brain fog, poor memory, difficulty concentrating
• Depression, anxiety, and mood instability
• Tingling or numbness in the hands, feet, or legs (peripheral neuropathy)
• Balance problems and difficulty walking
• Pale or jaundiced skin
• Inflamed, red, or swollen tongue (glossitis)
• Shortness of breath and heart palpitations
• Mouth ulcers and soreness

Why So Many People Are Deficient

B12 is found almost exclusively in animal products — meat, fish, eggs, and dairy. Vegetarians and vegans are at high risk. But even meat-eaters are commonly deficient due to absorption problems.

B12 absorption requires a protein called intrinsic factor, produced by the stomach lining. Intrinsic factor production declines with age, with atrophic gastritis, and with the use of proton pump inhibitors (PPIs) like omeprazole or H2 blockers. Metformin — one of the most prescribed medications in the US — directly blocks B12 absorption and causes deficiency in up to 30% of long-term users.

Additionally, B12 requires healthy gut function throughout the small intestine for absorption. IBS, Crohn's disease, celiac disease, and intestinal dysbiosis all compromise absorption.

Why B12 Injection Is Superior to Oral

Oral B12 supplementation depends entirely on the same absorption pathway that is compromised in most deficient people — intrinsic factor and healthy gut function. If your stomach isn't making enough intrinsic factor, a pill will do very little.

B12 injection (intramuscular) bypasses the gut entirely. The vitamin is delivered directly into muscle tissue and absorbed into the bloodstream without any dependence on digestive function. For people with absorption problems, injections are not just preferable — they're often the only effective option.

At Full Circle Function, we offer B12 nutrient injections as a standalone service or as part of a comprehensive care plan. The most effective form is methylcobalamin — the active form your cells actually use. See our full comparison in the cyanocobalamin vs methylcobalamin article.

Who Should Consider B12 Injections

• Anyone with confirmed or suspected B12 deficiency
• Vegetarians and vegans
• People over 50 with declining stomach acid production
• Long-term metformin users
• Anyone taking PPIs or H2 blockers long-term
• People with gut absorption issues (IBS, Crohn's, celiac)
• Those with unexplained fatigue, brain fog, or neuropathy
• People with MTHFR variants who need methylated B12

Frequently Asked Questions

What are the symptoms of vitamin B12 deficiency?

Symptoms include fatigue, brain fog, memory problems, depression, tingling or numbness in the hands and feet, balance issues, pale skin, and mouth soreness. Severe or long-term deficiency can cause permanent nerve damage.

What causes B12 deficiency?

Common causes include vegetarian/vegan diet, reduced stomach acid from aging or PPIs, long-term metformin use, gut absorption disorders (Crohn's, celiac, IBS), and intrinsic factor deficiency (pernicious anemia).

Is B12 injection better than oral B12?

For people with absorption problems — which includes most people who are deficient — B12 injection is significantly more effective than oral because it bypasses the gut entirely and does not depend on intrinsic factor.

What type of B12 is best for injections?

Methylcobalamin is the active, bioavailable form of B12 and is preferred over cyanocobalamin, which requires conversion and contains a small amount of cyanide. See our full comparison article for details.

Where can I get B12 injections in Wood River, IL?

Full Circle Function LLC offers methylcobalamin B12 injections at 21 E. Acton, Wood River, IL 62024. Call 618-254-2260 to schedule or ask about adding injections to your care plan.