Q. What are the effects of vitamin B12 deficiency if left untreated?

A. A deficiency of vitamin B12 can cause neurological and psychiatric problems that “can progress if left untreated, and can lead to irreversible damage,” said Dr. Donald Hensrud, director of the Mayo Clinic’s Healthy Living Program. Fortunately, it can be reversed fairly easily with vitamin pills or injections.

Vitamin B12 is required for proper red blood cell formation, nerve function and DNA synthesis. It is naturally present in fish, meat, eggs and dairy products, as well as some fortified breakfast cereals and nutritional yeast products.

Strict vegans who avoid animal products can develop a deficiency of B12 over time if they don’t take a supplement. But two-thirds of cases occur in the elderly, who are susceptible because they may not absorb adequate amounts of B12 from foods but who are not routinely tested, Dr. Hensrud said.

Consequences of B12 deficiency can cause a range of symptoms that include fatigue, weakness, constipation, loss of appetite and weight loss. Other symptoms include difficulty maintaining balance, depression, confusion, dementia, poor memory and soreness in the mouth or tongue.