The thing is, you might not know you have a deficiency straight off the bat. "You could have low B12 for years before an actual deficiency symptom shows up," says Robin Foroutan, MD, RDN, HHC, a spokesperson for the Academy of Nutrition and Dietetics.
A deficiency can lead to anemia and nervous system complications that cause symptoms like fatigue, numbness, tingling, muscle weakness, and shortness of breath as well as cognitive complications like memory loss and depression, Virga adds. And if left untreated for a long period of time, it can lead to severe, irreversible nerve damage in some cases.
Since vitamin B12 is found in meat, seafood, and dairy, there are some people with dietary restrictions who are more susceptible to a vitamin B12 deficiency—vegans and vegetarians, for example. "It's probably the most-difficult-to-absorb vitamin, and it's not found everywhere in food," Foroutan says. "Mostly animal foods are sources of B12, but because it's so difficult to absorb, a lot of people end up with low levels even if they might be eating the right amount of B12 foods. The people who are most at risk for B12 deficiencies or chronic low-grade insufficiencies are the vegetarians and vegans, anybody avoiding red meat and people who take acid-blocking medication or routinely take antacids."