B-12 deficiency isn’t just serious; it's more common than people realize. An estimated 48 million adults may be at risk for B-12 deficiency, while 2 in 5 Americans over the age of 60 may have some degree of B-12 deficiency.

"There are several reasons for this, but the predominant one is failure of the stomach and intestines to function normally," says Ralph Green, M.D., Ph.D., a noted authority on vitamin B-12.

Knowing your risk

People with gastrointestinal diseases, such as celiac disease, atrophic gastritis and Crohn's disease are at increased risk because B-12 can't be properly absorbed from food.

"There are many causes of B-12 deficiency, and often gastrointestinal problems are the root."

Two of 5 people with celiac disease and 1 in 5 people with Crohn's disease may be deficient in the vitamin. "There is a slew of people with gastrointestinal disorders who will have B-12 deficiency as aspect component," adds Green.

It may not be a doctor's first diagnosis, however. Symptoms, which can include abdominal pain, diarrhea and loss of appetite, can be easily attributed to other ailments.

Behind the symptoms

"We have all these intestinal diseases—Crohn's disease, celiac disease—and every one of them will cause symptoms of the underlying problem. So when these patients go to their doctors, they may diagnose what's wrong, but may not determine that there is an underlying B-12 deficiency," says Green.

The good news is that simple blood tests can expose a B-12 deficiency, and treatments are available. Monthly injections may work for some, and a new daily oral treatment recently became available.

Anyone who has a gastrointestinal ailment should request a blood test for B-12. As Green says, "There are many causes of B-12 deficiency, and often gastrointestinal problems are the root."