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Nexium & Absorption of Nutrients

By Chris Daniels ; Updated May 05, 2018

Nexium is the brand name for esomeprazole, an over-the-counter and prescription medicine that reduces acidity in the stomach. Nexium is part of a group of medications called proton-pump inhibitors (PPIs).

These medicines block the release of acid from cells lining the stomach. PPIs are very effective stomach acid reducers and are used to treat acid-related conditions, such as gastroesophageal reflux disease (GERD).

But Nexium may reduce the absorption of certain nutrients whose absorption is aided by stomach acid. These nutrients include iron, vitamin B12 and calcium. Nexium may also interfere with magnesium absorption through mechanisms unrelated to its acid reducing effects. Overall, the effects of PPIs on nutrient absorption are probably small in most people.


Iron is primarily absorbed in the first part of the small intestine. Up to one-third of iron in the diet is in the form of heme iron, which is not affected by stomach acidity. The rest of dietary iron is non-heme iron, which is influenced by acidity. Stomach acid converts non-heme iron to a form that is more easily absorbed. By decreasing stomach acidity, Nexium and other PPIs may reduce the absorption of iron.

A few small studies have reported reduced iron levels in people taking PPIs, although the decrease was usually small. A larger study involving 200 adults, published in “Open Access Macedonian Journal of Medical Sciences” in March 2018, produced similar results. Iron levels fell slightly, from an average of 17.6 micromole/liter before the study to 16.9 micromole/liter after 1 year of PPI use.

Vitamin B12

Vitamin B12 is absorbed in the last part of the small intestine. It is attached to proteins in food, and acid in the stomach is necessary to activate pepsin, an enzyme that releases vitamin B12 from these proteins.

A very large study of more than 200,000 people published in “JAMA” in December 2013 reported that people taking a PPI for at least 2 years had a 65 percent higher likelihood of low vitamin B12 levels than people who did not take any PPIs. Other, but not all, studies have also found reduced vitamin B12 levels in people taking PPIs, especially when used for a prolonged time.


Calcium is absorbed throughout the small intestine. Stomach acid aids absorption by helping separate calcium from ingested food and helping dissolve some forms of calcium. PPIs may interfere with these processes. But the overall importance of gastric acidity in calcium absorption is unclear. Likewise, the effects of PPIs on calcium absorption are controversial.

Some studies reported that PPIs reduce calcium absorption, but other studies reported that they don't. A study published in the December 2010 issue of “Journal of Bone and Mineral Research,” for example, found that PPI therapy did not affect calcium absorption at all. On the other hand, a study published in the July 2005 issue of "The American Journal of Medicine" reported that PPI treatment for as little as 1 week reduced calcium absorption.


Magnesium is absorbed throughout the small and large intestines and is generally not affected by stomach acid. Nevertheless, absorption of magnesium may be reduced with PPIs by various other mechanisms.

A study published in “Renal Failure” in June 2015 combined the results of several previous studies. It concluded that people taking PPIs were 43 percent more likely to have low magnesium levels than people not taking PPIs.

In 2011, the US Food and Drug Administration (FDA) issued a warning about the possibility of low magnesium, and indicated that periodic checking of blood magnesium levels should be considered when PPIs are taken for a prolonged time.

Warnings and Precautions

Before taking Nexium, see your doctor to determine the cause of your symptoms. Heartburn or other symptoms that may seem to be caused by GERD may actually be due to other conditions, such as heart disease or cancer.

If your doctor recommends Nexium, she may suggest dietary changes to counteract the possibility of reduced nutrient absorption. Your doctor may also recommend intermittent blood tests, such as iron, vitamin B12, calcium or magnesium levels, especially if you take Nexium for several months or longer.

Reviewed and revised by Mary D. Daley, M.D.

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