Sneaky signs of low stomach acid

By Dr. Nathalie Beauchamp, DC

This blog is intended for educational purposes only and should not be used to diagnose or treat any medical condition. Always consult your primary healthcare provider before making changes to your health routine or acting on the information shared here.

Are you doing everything right—eating well, taking your supplements, avoiding foods that seem to bother you—yet something still feels off? Maybe you’re inexplicably exhausted despite getting enough sleep. Your lab work shows nutrient deficiencies even though your diet looks good on paper. Or digestive discomfort lingers no matter how carefully you eat. If this sounds familiar, you might be missing a crucial piece of the puzzle.

That missing piece could be stomach acid. Most people have heard plenty about too much acid causing reflux and ulcers, but far fewer know that too little acid is equally problematic, and arguably more common. When stomach acid levels drop, a cascade of issues follows: poor protein breakdown, impaired nutrient absorption, bacterial overgrowth, and a weakened first line of immune defense.

This blog explores the critical role stomach acid plays in your health, why levels decline, how to recognize the signs of low stomach acid, and what you can do to support optimal digestive function naturally.

Stomach acid: the foundation of healthy digestion

Stomach acid, also called gastric acid, is primarily composed of hydrochloric acid (HCl), which is produced by specialized cells called parietal cells that line your stomach wall. Stomach acid performs several precise, interconnected functions that are essential to your overall health.

1. Breaking down proteins

When you eat protein—whether from chicken, beans, eggs, or any other source—those protein molecules are tightly wound structures. Stomach acid works to denature these proteins, which means it unfolds and loosens their complex three-dimensional shape. Think of it like untangling a ball of yarn so you can work with individual strands. This unfolding is critical because it exposes the inner structure of the protein, making it accessible to digestive enzymes that can then break it down into smaller fragments called peptides.

2. Activating your digestive enzymes

Your stomach produces an enzyme called pepsinogen, which is initially inactive—a safety feature that prevents it from digesting the cells that produce it. Stomach acid transforms pepsinogen into its active form, pepsin, which is one of your primary protein-digesting enzymes. Pepsin only works properly in a highly acidic environment (a pH of around 1.5 to 2), so without adequate stomach acid, this crucial enzyme remains largely dormant, and protein digestion suffers.

3. Creating chyme

As your stomach acid and enzymes work on your food, they transform it from recognizable chunks into a semi-liquid mixture called chyme. This consistency is important because it allows for more efficient movement into the small intestine and ensures that nutrients are in a form that can be properly absorbed. If the food leaving your stomach isn’t acidic enough or isn’t broken down sufficiently, you may experience bloating, gas, discomfort, or irregular bowel movements.

4. Coordinating the digestive process

Stomach acid also serves as a signal coordinator for the rest of your digestive system. When acidic chyme enters the small intestine, its acidity triggers the release of hormones like secretin and cholecystokinin (CCK). These hormones tell your pancreas to release digestive enzymes and signal your gallbladder to release bile—both essential for breaking down fats, carbohydrates, and proteins in the small intestine. If the chyme entering your small intestine isn’t acidic enough, these signals are weaker, and the entire downstream digestive process becomes less efficient. This is why people with low stomach acid often experience digestive symptoms that seem unrelated to the stomach itself.

Stomach acid and nutrient absorption: the critical link

Adequate stomach acid is fundamental to whether you can actually extract and absorb the nutrients from your food. We’ve all heard the phrase, ‘you are what you eat’, but in reality, it should be, ‘you are what you ABSORB.’ Several critical nutrients depend on proper stomach acid for absorption:

Vitamin B12

Vitamin B12 is bound to proteins in the foods you eat (meat, fish, dairy, eggs). Stomach acid is required to cleave B12 away from these proteins so it can then bind to a substance called intrinsic factor, which is also produced in the stomach. Only after binding to intrinsic factor can B12 be absorbed later in the small intestine. Without sufficient stomach acid, this process breaks down, and B12 deficiency can develop even if you’re eating plenty of B12-rich foods. Over time, low B12 leads to fatigue, neurological symptoms, mood changes, and cognitive issues like memory problems and brain fog. ⁽¹⁾

Minerals: iron, calcium, magnesium, and zinc

Stomach acid plays a key role in mineral absorption. For iron, the acid converts it from its food-bound form (ferric iron) into a more absorbable form (ferrous iron). This is especially important for non-heme iron from plant foods. Calcium, magnesium, and zinc also require an acidic environment to be released from food and made available for absorption in the intestines. When stomach acid is low, mineral deficiencies can develop silently, showing up months or years later as issues like anemia (from low iron), weakened bones (from low calcium), muscle cramps or irregular heartbeat (from low magnesium), poor wound healing, or weakened immunity (from low zinc).

Protein and amino acids

Because stomach acid is essential for protein digestion, low acid means fewer amino acids are available for absorption. Amino acids are the building blocks your body uses to make neurotransmitters (like serotonin and dopamine), hormones, muscle tissue, enzymes, and immune cells. Inadequate amino acid availability can contribute to mood disorders, difficulty building or maintaining muscle, poor recovery from exercise, thinning hair, brittle nails, and a weakened immune response. ⁽²⁾

One of the most frustrating aspects of low stomach acid is that people can develop nutrient deficiencies even when their diet looks excellent on paper. Over time, this can manifest as chronic fatigue, hair loss, pale skin, brittle nails, anxiety, depression, difficulty concentrating, frequent infections, and slow recovery from illness or injury.

Beyond digestion and nutrient absorption, stomach acid serves as one of your body’s primary defence systems against infection. The highly acidic environment of the stomach acts as a chemical barrier that kills or significantly weakens most bacteria, viruses, parasites, and yeasts that enter your body through food and water. Think of your stomach as a security checkpoint—pathogens that make it through have already been screened and drastically reduced in number.

What happens when the barrier weakens

When stomach acid is low (a condition called hypochlorhydria) or absent (achlorhydria), this protective barrier is compromised. Microbes that would normally be destroyed in the stomach survive the journey and move into the small intestine, where they don’t belong. This can lead to several problems:

Small intestinal bacterial overgrowth (SIBO): Normally, the small intestine has relatively few bacteria because stomach acid, bile, and the migrating motor complex (a cleaning wave between meals) keep it clear. When stomach acid is weak, bacteria from food or from the mouth can colonize the upper small intestine. These bacteria ferment carbohydrates, producing gas and causing bloating, abdominal pain, diarrhea, or constipation.

Gut microbiome disruption: The balance of bacteria throughout your digestive tract can shift when pathogens aren’t properly controlled in the stomach. This dysbiosis (imbalance in gut bacteria) has been linked to inflammation, immune system dysfunction, nutrient malabsorption, and even mental health symptoms through the gut-brain axis. ⁽³⁾

Increased infection risk: Research has shown that people with low stomach acid are more susceptible to gastrointestinal infections from bacteria like Salmonella, C. difficile, and Campylobacter, as well as parasites like Giardia. ⁽⁴⁾ They’re also more likely to experience traveller’s diarrhea and foodborne illness.

Systemic inflammation: When harmful microbes establish themselves in places they shouldn’t be, the immune system responds with inflammation. Chronic low-grade inflammation has been implicated in conditions ranging from joint pain and skin issues to autoimmune disease and metabolic disorders. ⁽⁵⁾

The ripple effect

Low stomach acid creates a domino effect: inadequate protein digestion leads to fewer available amino acids, which means less raw material for immune cells and antibodies. Poor mineral absorption (especially zinc) further weakens immune function. Disrupted gut bacteria produce inflammatory compounds and interfere with the gut barrier, allowing particles into the bloodstream that trigger immune responses. All of this can manifest as frequent colds, slow healing, chronic sinus infections, skin problems, food sensitivities, or autoimmune flares—symptoms that may seem completely unrelated to stomach acid, yet all trace back to that initial digestive breakdown.

Symptoms and signs of low stomach acid

Low stomach acid rarely shows up as one clear, telltale symptom. Instead, it tends to show up as a cluster of issues that can affect both your digestion and your overall health. No single sign can diagnose low stomach acid on its own, but when several of these symptoms appear together and persist over time, they create a pattern that’s worth taking seriously and investigating further. 

**Please note—several of these symptoms overlap with many other medical conditions, assessment should always consider the whole picture and rule out serious disease.**

Early fullness and post-meal discomfort: One of the hallmark signs of low stomach acid is feeling uncomfortably full after eating what should be a normal-sized meal, or even a small one. You might feel a sense of heaviness or pressure in your upper abdomen, as though food is just sitting there like a brick. This happens because without adequate acid, food isn’t being broken down efficiently. Instead of being transformed into that semi-liquid chyme that can move smoothly into the small intestine, it lingers in the stomach, creating that “stuck” sensation. 

Burping and gas soon after eating: Excessive burping or belching within 30 minutes to an hour after a meal can be a telltale sign of hypochlorhydria. ⁽⁶⁾ When proteins aren’t properly broken down due to insufficient acid, they begin to ferment in the stomach. This fermentation produces gas, which has to go somewhere—usually up. While occasional burping is normal, frequent, uncomfortable belching after meals, especially protein-rich meals, suggests that food isn’t being processed as it should be. This is different from the bloating that might occur several hours later from bacterial fermentation in the intestines; this happens early and high in the digestive tract.

Heartburn and reflux: This is perhaps the most counterintuitive symptom: low stomach acid can actually cause heartburn and acid reflux. Most people assume heartburn means they have too much acid, which is why antacids and acid-blocking medications are so commonly used. However, when stomach acid is low, the lower esophageal sphincter (the valve between your esophagus and stomach) doesn’t receive the proper signal to stay tightly closed. This valve needs adequate acidity to maintain its tone. Additionally, undigested food sitting in the stomach creates pressure, and even small amounts of acid can splash up into the esophagus, causing that burning sensation. You might also experience regurgitation—bringing up small amounts of food or liquid hours after eating, or waking up at night with acid in your throat.

Changes in stool and bowel habits: Your stool can tell you a lot about your digestion. With low stomach acid, you might notice visible pieces of undigested food, particularly vegetables, nuts, or seeds. This happens because food that wasn’t properly broken down in the stomach can’t be fully processed in the intestines either. You might experience constipation because poorly digested food moves slowly through the system, or you might have loose, poorly formed stools because undigested food particles irritate the intestinal lining. Some people alternate between the two, creating a frustrating pattern of digestive unpredictability. The stool might also be pale or greasy-looking, indicating poor fat digestion (which often follows poor protein digestion, since protein breakdown triggers bile release).

Hair, skin, and nail changes: Your body is remarkably efficient at prioritizing resources. When nutrients are scarce, it sends them to vital organs first—your hair, skin, and nails are lower on the priority list. This is why these tissues often show the first visible signs of nutrient deficiency. Hair loss or thinning, particularly diffuse thinning across the whole scalp rather than in a pattern, can indicate low iron, zinc, or protein absorption. Your nails might become brittle, develop vertical ridges, or break easily. They might even start to spoon (curve upward at the edges), a classic sign of iron deficiency. Your skin may become dry, pale, or lose its usual glow. You might bruise more easily because you’re not absorbing enough vitamin C and bioflavonoids, or because low protein levels affect blood vessel integrity.

Compromised immunity and poor healing: If you’re catching every cold that goes around, if minor cuts take weeks to heal, or if you’re dealing with recurrent skin issues like acne, eczema, or fungal infections, low stomach acid could be a contributing factor. This happens through multiple pathways. First, you’re not absorbing the zinc, vitamin C, vitamin A, and protein needed for a robust immune response and tissue repair. Second, because stomach acid isn’t killing pathogens effectively, you’re experiencing more frequent infections. Third, if SIBO or dysbiosis has developed, the resulting inflammation keeps your immune system in a constant state of activation, exhausting its resources. You might notice that you’re always getting sick, that you’re the first person in the office to catch a bug, or that infections that should clear up quickly seem to linger for weeks.

Additional subtle signs: Beyond these major categories, low stomach acid can manifest in ways that seem unrelated until you understand the connection. You might develop food sensitivities or intolerances you never had before, because poorly digested food particles trigger immune reactions. You might have a white coating on your tongue, bad breath despite good oral hygiene, or a persistent sour taste in your mouth. Some people develop angular cheilitis (cracks at the corners of the mouth) from B-vitamin deficiencies. You might notice that you feel anxious or depressed—neurotransmitters like serotonin require adequate amino acid building blocks, which you’re not getting from poorly digested protein.

Why stomach acid declines

Understanding that you might have low stomach acid raises an obvious question: why? What causes this fundamental digestive function to weaken? The answers are varied and often interconnected.

Aging: Gastric acid secretion tends to decline with age. Older adults are more likely to have hypochlorhydria due to changes in parietal cell function, chronic infections, and higher use of acid-suppressing medications. This helps explain why nutrient deficiencies (particularly B12 and iron) and gut infections are more common in older populations.?

Medications and medical conditions: Longterm use of proton pump inhibitors (PPIs), H2 blockers, and frequent over-the-counter antacid use can significantly lower stomach acid levels. These drugs can be very helpful and sometimes necessary in the short term, but chronic use without addressing root causes may lead to impaired protein digestion, reduced nutrient absorption, and higher infection risk.?⁽⁷⁾

Other medical causes of low acid include:

• Chronic Helicobacter pylori infection damages the stomach lining and parietal cells.
• Autoimmune gastritis and pernicious anemia, where the immune system targets acid?producing cells and intrinsic factor.?
• Longstanding chronic illness, severe stress, and inflammatory conditions that disrupt gastric mucosa and regulatory signals.

Lifestyle and diet factors: Our modern lifestyles place a heavy burden on the digestive system, creating numerous obstacles to maintaining healthy stomach acid levels. Key contributors to low stomach acid include:

• Chronic stress, which disrupts digestive signaling and reduces acid production
• Diets high in processed foods, excessive sugars, and low in fiber, which negatively impact digestive function
• Eating quickly or while distracted, leading to poor chewing and reduced digestive readiness
• Sedentary habits that slow down digestion and gut motility
• Excessive alcohol consumption and smoking, both of which can damage the stomach lining and impair acid secretion
• Overuse of certain medications such as NSAIDs that irritate the digestive tract

It’s rarely just one factor that causes low stomach acid. More often, it’s a combination: perhaps you’re in your 50s (age factor), you’ve been taking a PPI for several years for heartburn (medication factor), you eat lunch at your desk while answering emails (stress factor), and your diet includes a lot of processed convenience foods (diet factor). Each element compounds the others, progressively weakening your stomach’s ability to produce adequate acid. 

The good news is that many of these factors are within your control, and even modest changes can begin to shift the trajectory toward better digestive function.

Could Heartburn Be From Too Little Acid?

It seems counterintuitive, but low stomach acid can drive many of the symptoms commonly blamed on excess acid:

• Bloating and pressure after meals.
• Belching, gas, and a sour or metallic taste.
• Heartburn and reflux, especially when lying down.
• A sensation of food “just sitting there” for hours.?

When food is not properly broken down, it tends to linger and ferment, producing gas and increasing pressure in the stomach. That pressure can push stomach contents—including even a small amount of acid—upward through a lax or overwhelmed lower esophageal sphincter, irritating the esophagus. The burning is real, but the underlying driver may not be an overproduction of acid; it may be poor digestion, slow motility, and inadequate acidity.?

Conventional statistics often focus on documented GERD or acid hypersecretion, while low stomach acid is historically underdiagnosed because direct testing is less commonly done. Many integrative and functional clinicians report that hypochlorhydria is very common in practice, particularly in older adults and people on long-term acid-suppressing medication, although precise percentages vary depending on the population and testing method.?

The antacid and PPI rebound effect

Acid-suppressing medications and antacids are heavily marketed because they work quickly on symptoms. They either neutralize existing acid (antacids) or block acid production (PPIs and H2 blockers), which can provide real relief when the esophagus is inflamed or ulcers are present.

However, there are two big concerns with long-term use:

1. Rebound acid hypersecretion
When someone takes PPIs or strong acid-suppressors for an extended period and then stops abruptly, the body may temporarily overproduce acid as the system recalibrates. This rebound can make symptoms feel even worse than before, driving people back to the medication and creating a cycle of dependency.

2. Chronic under-acidity and downstream consequences
Ongoing suppression of stomach acid can worsen or induce hypochlorhydria, contributing to nutrient deficiencies, altered gut microbiota, and increased infection risk. ⁽⁸⁾ If the original problem was related more to motility, sphincter function, or food triggers than true overproduction, long-term suppression may not address the root cause.

Anyone on prescription acid-suppressing medication should never adjust or discontinue use without the guidance of the prescribing clinician.

For natural strategies for beating acid reflux naturally, you can read a previous blog I wrote here.

How the nervous system influences stomach acid production

Digestion is a highly coordinated physiological process that depends heavily on the nervous system. The vagus nerve, which mediates the parasympathetic “rest-and-digest” response, is instrumental in stimulating acid secretion. This is especially evident during the cephalic phase of digestion—when the mere sight, smell, or thought of food prompts the brain to signal the stomach to produce acid and digestive enzymes in anticipation.

Modern lifestyles often interfere with this neurophysiological signalling. Chronic stress activates the sympathetic “fight-or-flight” sympathetic nervous system. In this state, the body shunts resources away from digestion, and vagal signalling to the stomach diminishes. The result: sluggish acid production, weaker motility, and more chances for reflux, even if overall acid output is not excessive.

Simple practices that support vagal tone can make a tangible difference in digestion:

• Taking a few slow, deep breaths before meals.
• Sitting down to eat, away from work and screens.
• Chewing thoroughly and eating more slowly.
• Gentle humming, gargling, or singing, which can stimulate parts of the vagus nerve and throat musculature.?

For some, addressing nervous system regulation is as important as any supplement when it comes to improving stomach acid and reflux patterns.

So, how do you know if you have adequate stomach acid?

By now, you might be recognizing yourself in some of these symptoms and wondering whether low stomach acid could be part of your picture. While the patterns can be suggestive, symptoms alone don’t give you definitive answers—many conditions share similar signs, and it’s important to understand what’s actually happening rather than guessing.

Unfortunately, direct testing for stomach acid isn’t simple or widely accessible. The gold standard medical test involves swallowing a capsule that measures stomach pH over time, but it’s expensive, rarely available, and seldom ordered outside of specific medical situations. Standard endoscopy can reveal stomach inflammation, but doesn’t measure acid production directly.

One of the most accessible methods is the betaine HCL test—a simple, inexpensive way to assess whether your stomach is producing adequate acid.

The Betaine HCL Test: At-Home Assessment 

Betaine HCL (hydrochloride) is a supplement that combines betaine, a compound naturally found in beets, spinach, and whole grains, with hydrochloric acid, the same acid your stomach produces. The test uses a simple principle: if your stomach already has enough acid, adding more will cause discomfort. If acid is low, supplementation should improve digestion without causing any burning sensation.

A betaine HCl trial should be avoided—or only done under close professional supervision—if someone has:

• A history of peptic ulcers or gastric bleeding.
• Active gastritis or known esophageal damage.
• Use of NSAIDs, steroids, blood thinners, or ongoing acid-suppressing drugs.

To perform the betaine HCL test:

1. Purchase betaine HCL supplements: Betaine HCL supplements can be found at most health food stores or online. Look for a supplement that contains at least 650 milligrams of betaine HCL.
2. Begin with a low dose: Start with a low dose of betaine HCL, such as one capsule of 650 milligrams, and take it with a protein-rich meal.
3. Observe any changes: After taking the supplement, pay attention to any changes in digestion. You may feel a warming or burning sensation in your stomach or notice improved digestion, such as less bloating or gas.
4. Increase the dose: If you do not notice any changes in digestion, gradually increase the dose of betaine HCL by one capsule at a time with each meal, up to a maximum of six capsules.
5. Find the right dosage: Once you feel a warming or burning sensation in your stomach, or notice improved digestion, reduce the dosage by one capsule until you find the lowest effective dose.

10 ways to support healthy stomach acid production naturally

Maintaining optimal stomach acid is key to effective digestion, nutrient absorption, and overall gut health. Fortunately, many natural strategies can help support the stomach’s acid-producing ability:

1. Practice mindful eating: Taking the time to eat slowly and chew thoroughly encourages saliva production and signals your digestive system to prepare acid and enzymes. This early stimulus is vital for strong acid secretion.

• Manage stress proactively: Chronic stress interferes with the nervous system’s impact on stomach acid production. Techniques such as deep breathing, meditation, gentle yoga, or short walks can reduce stress hormones that dampen acid secretion.

• Include digestive bitters: Natural bitters found in foods like dandelion greens, arugula, endive, and radicchio stimulate taste receptors that activate digestive secretions, including stomach acid.

• Eat smaller, well-timed meals: Large or irregular meals may overwhelm the stomach and impair acid production. Smaller, evenly spaced meals support consistent acid secretion and prevent overburdening the digestive tract.

• Limit processed foods and sugars: Diets high in refined sugars and processed ingredients promote gut inflammation and an unhealthy microbiome, both of which can negatively affect acid levels.

• Stay optimally hydrated: Drinking adequate water throughout the day supports digestion, but avoid drinking large volumes during meals as this can dilute stomach acid and disrupt its function. Sip fluids lightly around mealtimes.

• Support gut microbial balance: A healthy microbiome supports overall digestive function. Consuming fermented foods like yogurt, kefir, sauerkraut, kimchi, or taking targeted probiotics can nurture beneficial bacteria that indirectly promote stomach acid health.

• Incorporate zinc and other nutrients: Zinc is critical for the function of the parietal cells that produce acid. Ensuring sufficient zinc intake via food sources like pumpkin seeds, oysters, and beef, or via supplementation if needed, benefits acid production.

• Consider digestive enzyme or betaine HCl supplementation: For some individuals, supplements like betaine hydrochloride can directly support acid levels. Digestive enzymes may also aid digestion when acid production is low.

1. Limit or carefully manage acid-suppressing medications: Long-term use of PPIs or H2 blockers can impair natural acid production. If these medicines are necessary, work with your healthcare provider on tapering strategies and supporting gut recovery.

Remember: digestion is foundational to everything else your body does. When you properly break down food and absorb nutrients, the benefits ripple outward—better energy, clearer thinking, stronger immunity, and improved overall vitality.

Your body has remarkable healing capacity when given the right support. Start with small changes, pay attention to how you respond, and trust that better digestion is absolutely within reach.

Yours in health,
Dr. Nathalie

Dr. Nathalie Beauchamp, B.Sc., D.C., IFMCP is the author of the book—Hack Your Health Habits: Simple, Action-Driven, Natural Solutions For People On The Go, and the creator of several online health education programs. Dr. Nathalie’s mission is to educate, lead and empower people to take control of their health. She recently launched a new book https://smartcuts.life/
For health strategies and biohacking tips sign up for her newsletter at www.drnathaliebeauchamp.com

Photo credit: © Africa Images via Canva.com

References:

1. Jatoi, S., Hafeez, A., Riaz, S. U., Ali, A., Ghauri, M. I., & Zehra, M. (2020). Low vitamin B12 levels: An underestimated cause of minimal cognitive impairment and dementia. Cureus, 12(2), e6976. https://doi.org/10.7759/cureus.6976
2. Teng T, Huang F, Xu M, Li X, Zhang L, Yin B, Cai Y, Chen F, Zhang L, Zhang J, Geng A, Chen C, Yu X, Sui J, Zhu ZJ, Guo K, Zhang C, Zhou X. Microbiota alterations leading to amino acid deficiency contribute to depression in children and adolescents. Microbiome. 2025 May 19;13(1):128. doi: 10.1186/s40168-025-02122-w. PMID: 40390033; PMCID: PMC12087099.
3. Clapp M, Aurora N, Herrera L, Bhatia M, Wilen E, Wakefield S. Gut microbiota’s effect on mental health: The gut-brain axis. Clin Pract. 2017 Sep 15;7(4):987. doi: 10.4081/cp.2017.987. PMID: 29071061; PMCID: PMC5641835.
4. Levine, M. M., & Snyder, M. J. F. (2008). Influence of gastric acidity on susceptibility to infection with ingested bacterial pathogens. Infection and Immunity, 76(9), 4684–4690. https://doi.org/10.1128/IAI.01138-07
5. Chavda VP, Feehan J, Apostolopoulos V. Inflammation: The Cause of All Diseases. Cells. 2024 Nov 18;13(22):1906. doi: 10.3390/cells13221906. PMID: 39594654; PMCID: PMC11592557.
6. Cleveland Clinic. (2025). Hypochlorhydria (Low Stomach Acid): Symptoms, Tests & Treatments. Retrieved November 25, 2025, from https://my.clevelandclinic.org/health/diseases/23392-hypochlorhydria
7. Freedberg, D. E., Kim, L. S., & Yang, Y. X. (2017). The risks and benefits of long-term use of proton pump inhibitors: Expert review and best practice advice from the American Gastroenterological Association. Gastroenterology, 152(4), 706–715. https://doi.org/10.1053/j.gastro.2017.01.031
8. Heidelbaugh JJ. Proton pump inhibitors and risk of vitamin and mineral deficiency: evidence and clinical implications. Ther Adv Drug Saf. 2013 Jun;4(3):125-33. doi: 10.1177/2042098613482484. PMID: 25083257; PMCID: PMC4110863.