Drugs that reduce acid production can make it harder for the stomach to absorb vitamin B12.
Acid-inhibiting drugs like Zantac and Prilosec have become hugely popular because they're so good at preventing the unpleasant symptoms of heartburn and acid indigestion.
But the drugs also make it more likely that a person will be short on vitamin B-12. And that can contribute to health problems including depression, nerve damage and dementia.
People who took acid-inhibiting drugs for two or more years were more likely to have B-12 deficiency, according to a study published Tuesday in JAMA, the journal of the American Medical Association. The more medication they took, the more apt they were to be short on the vitamin.
That was particularly true if they took drugs called proton pump inhibitors, which can suppress 90 percent of stomach acid. Over-the-counter brand names for those include Prevacid and Prilosec.
Other acid-inhibiting drugs, called histamine 2 receptor antagonists, also increased the risk of B-12 deficiency, but not as much. They're sold over-the-counter as Pepcid, Tagamet and Zantac, among other names.
In the study, 12 percent of the people taking proton pump inhibitors for two years or more developed a new diagnosis of B-12 deficiency, compared to 4 percent who were taking histamine 2 receptor antagonists.
When people in the study stopped taking the acid inhibitors, their B-12 levels rose.
As part of the study, the researchers looked at the records of almost 26,000 patients at Kaiser Permanente clinics in Northern California who were diagnosed with B-12 deficiency between 1997 and 2011.
It's the biggest study by far to look at how acid-inhibiting drugs affect B-12. Earlier efforts also found a link, but looked at much smaller numbers of people.
Vitamin B-12 deficiency is relatively common, especially in older people, and can cause a wide range of symptoms, including tiredness, weakness, depression, weight loss, a loss of appetite and anemia. More serious problems can include dementia and permanent nerve damage.
About 3 percent of adults over 50 are low in B-12, according to data from the Centers for Disease Control and Prevention.
People typically get their B-12 from food; it's in animal proteins, and also in some fortified cereals. Stomach acid shears the B-12 from food proteins and makes it easier for the body to absorb. So when there's less acid, there's less B-12 available.
Fortunately, this is an easy problem to solve: Take vitamin B-12 supplements, or stop taking the acid inhibitors.