Antacids are commonly used to neutralize the acid in the stomach, helping many individuals who have acid reflux. But a new study suggests that using this medication consistently for 2 years or more is linked to a deficiency of vitamin B12, which can have adverse effects for the nervous system.

The research, published in JAMA, is among the first to show associations between long-term exposure to antacids and vitamin B12 deficiency in a large population-based study.

The investigators say that antacids, including proton pump inhibitors (PPIs) and histamine 2 receptor antagonists (H2RAs), are some of the most commonly used pharmaceuticals in the US.

However, because they suppress the creation of gastric acid, the team says antacids may lead to malabsorption of vitamin B12. This vitamin helps to keep the nervous system - consisting of the brain, nerves and spinal cord - healthy.

"Vitamin B12 deficiency is relatively common," say the researchers, "especially among older adults; it has potentially serious medical complications if undiagnosed."

They continue:

"Left untreated, vitamin B12 deficiency can lead to dementia, neurologic damage, anemia and other complications, which may be irreversible."

To conduct their study, the researchers, led by Jameson R. Lam of Kaiser Permanente in California, looked at the link between using antacids and vitamin B12 deficiency within the Northern California population of Kaiser Permanente patients.

Stronger association in women and younger age groups

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The study found a link between 2 years' use of antacids or more and a deficiency of vitamin B12.

With a study population consisting of 25,956 vitamin B12-deficient patients and 184,199 control patients without the deficiency, the researchers compared their use of acid inhibitors by using electronic pharmacy, laboratory and diagnostic databases.

They found that among the patients who were newly diagnosed with a vitamin B12 deficiency, 12% were given a 2-year or more supply of PPIs, compared with 7.2% of patients who were exposed to PPIs in the control group.

Similarly, 4.2% of the vitamin-deficient patients had a 2-year or more supply of H2RAs, versus 3.2% in the control group.

The researchers say that receiving a 2 or more years' supply of either of these medications was associated with a greater risk for becoming vitamin B12 deficient. They add that doses over 1.5 PPI pills per day were more strongly linked to the deficiency than doses under 0.75 pills per day.

Though they say cannot completely rule out confounding factors as they relate to their findings, they do note that using antacids "identifies a population at higher risk of B12 deficiency."

The magnitude of the association was stronger in women and younger age groups, they add, noting that the association decreased after patients stopped using the antacids.

The authors conclude:

"These findings do not recommend against acid suppression for persons with clear indications for treatment, but clinicians should exercise appropriate vigilance when prescribing these medications and use the lowest possible effective dose."

Vitamins have been a hot topic of late. A recent study cast doubts over vitamin D supplementation, while another suggested that low vitamin B9 in males' diets could cause birth defects in offspring.