About 3.6% of US adults have B12 deficiency by a common blood cutoff (below 200 pg/mL), and about 12.5% have insufficient levels (below 300 pg/mL), with similar rates in people 60 and older; other markers give higher figures in older adults. Deficiency is more likely in older adults, vegans and long-term users of metformin or acid-reducing medicines. Neurological symptoms can appear without anemia, so early diagnosis matters to avoid irreversible damage.
Common symptoms
Fatigue, weakness and shortness of breath (from megaloblastic anemia)
Numbness or tingling in the hands and feet
Memory problems or confusion
Low mood (associated with low B12 in some studies)
Sore, swollen tongue (glossitis)
Pale skin and palpitations
Balance problems or unsteady walking in advanced cases
At-risk groups
Vegans and strict vegetarians (B12 is found naturally only in animal foods)
Older adults, especially with atrophic gastritis
Long-term metformin users
Long-term users of proton pump inhibitors or H2 blockers
People with pernicious anemia (lack of intrinsic factor)
People who have had stomach or intestinal surgery, including weight-loss surgery
People with gastrointestinal disorders such as Crohn's disease or celiac disease
When to see a doctorIf you are in an at-risk group and have persistent fatigue together with numbness, tingling, balance problems or memory problems, ask your doctor for a B12 blood test. Methylmalonic acid is the most sensitive marker when B12 is borderline.