Low Stomach Acid and Heartburn: Why You May Not Be Absorbing Your Nutrients

When my first Functional Medicine practitioner ran my testing, low stomach acid showed up on the same page as Hashimoto's and SIBO. It was the piece I had never heard of, and it explained why years of good food had left me so depleted.

A lot of times people are put on PPIs, but what's actually more common is that we have low stomach acid. We're not absorbing nutrients.

That is my experience, and the experience of many Women I work with. The research on how common low stomach acid is in Midlife is more mixed than that, and this chapter gives you both, so you can bring the right questions to your practitioner.

Digestion has a long memory. Years of acid reducers, rushed meals, or an untested H. pylori infection in your 20's and 30's can leave a stomach that absorbs less iron, B12, and protein in your 40's and 50's, and the care you give your stomach now shapes how well you are nourished at 60 and beyond.

What happens in your stomach decides how much of your protein, iron, B12, and minerals you actually receive. 'The Gut, In Depth', the next chapter, follows your food further down.

What Your Stomach Acid Does All Day

The lining of your stomach holds parietal cells, and they make hydrochloric acid. That acid has several jobs at once.

• It digests protein. Acid unfolds proteins and switches on pepsin, the enzyme that begins cutting them apart. Without it, protein leaves your stomach in larger pieces than your gut is built to handle.
• It releases B12 from food. Acid and stomach enzymes free B12 from the protein it is bound to. The same parietal cells make intrinsic factor, the protein that carries B12 into your body at the end of your small intestine.
• It helps you absorb iron. Iron from plants, eggs, and supplements, called nonheme iron, depends on acid. In a 1981 study, an antacid cut nonheme iron absorption from a meal by 52 percent.
• It helps you absorb calcium, zinc, and magnesium. Acid dissolves calcium carbonate. Lowering acid with an H2 blocker reduced zinc absorption in a small study of healthy volunteers, and long-term acid-blocking medication can lower magnesium, as you will read below.
• It guards the door. Acid kills most of the bacteria, yeast, and parasites that arrive on your food, long before they reach your small intestine.
• It starts the relay. When acidic food enters your small intestine, it releases a hormone called secretin, which tells your pancreas to send bicarbonate. Fat and protein release a second hormone, CCK, which squeezes your gallbladder and calls for pancreatic enzymes.

The iron study's authors found that a healthy stomach makes more acid than iron absorption strictly needs, and absorption fell only when acid was markedly reduced. A modest dip may cause no trouble, while a stomach that makes very little acid can leave a Woman short on iron for years.

Calcium follows the same pattern. In people who make no stomach acid, calcium carbonate taken on an empty stomach was barely absorbed, 4 percent compared with 45 percent for calcium citrate.

Taken with breakfast, the same calcium carbonate was absorbed normally. Food itself helps, which is 1 more reason the Bones chapter teaches calcium from food.

Why Stomach Acid Can Fall

Low stomach acid is called hypochlorhydria, and almost none is achlorhydria. Several things can lower it, and some matter far more than others.

Age, and what travels with it. Many Functional Medicine sources say stomach acid falls steadily with age. The research tells a more specific story.

• In a 1996 study of 206 healthy adults aged 18 to 98, acid output was similar in young adults and in adults aged 35 to 64. It ran about 30 percent lower after 65, and that drop was explained by atrophic gastritis, H. pylori, and smoking, with no independent effect of age itself.
• Pepsin, the protein-digesting enzyme, fell about 40 percent in the older group, and age itself did predict lower pepsin.
• In a 1997 study of 248 adults over 65, nearly 90 percent could still make an acidic stomach, and most of those who could not showed markers of atrophic gastritis.

So the fuller picture is this. Low stomach acid becomes more common with age mainly because the conditions that damage the stomach lining become more common. Atrophic gastritis affects about 2 percent of the general population and 8 to 9 percent of adults 65 and older, according to the NIH Office of Dietary Supplements.

Autoimmune gastritis and Hashimoto's. Many Women with Hashimoto's have never heard of this link. In Autoimmune gastritis, the immune system targets the parietal cells, so the stomach gradually loses its ability to make both acid and intrinsic factor.

• Hashimoto's has been linked to gastric disorders in 10 to 40 percent of patients, and about 40 percent of people with Autoimmune gastritis also have Hashimoto's. The pairing has a name: thyrogastric syndrome.
• Iron deficiency often shows up first. B12 deficiency and pernicious anemia tend to follow later, as more of the lining is lost.
• In a study of 379 people with Autoimmune gastritis, 70 percent were Women and the median age was 55. More than half had digestive symptoms, most often a heavy, too-full feeling after meals.

That age, 55, sits right in the middle of Midlife. If you have Hashimoto's and an iron level that will not climb, Autoimmune gastritis belongs on your list of questions. The Thyroid chapter's section on the Multiple Autoimmune Reactivity Screen describes a panel that includes parietal cell and intrinsic factor antibodies.

The American Gastroenterological Association advises that people with Autoimmune gastritis be checked for iron and B12 deficiency, screened for Autoimmune thyroid disease, and offered an upper endoscopy to look for small growths called gastric neuroendocrine tumors. This diagnosis calls for regular follow-up with a gastroenterologist.

H. pylori. This stomach bacterium lives in an estimated 44 percent of adults worldwide, and it can stay quiet for years.

It is the most common cause of atrophic gastritis. Depending on where in the stomach it settles, it can raise acid and cause ulcers, or inflame the acid-making lining and lower acid over time.

Your thyroid. Dr. Datis Kharrazian names hypothyroidism itself as a cause of low stomach acid in his clinical model. The research here is small and mixed.

• In a study of 14 Women treated for hypothyroidism, acid output was lower only in those who also carried thyroid and parietal cell antibodies.
• In 9 people made deeply hypothyroid for several weeks during thyroid cancer care, acid output did not change.

The clearest thread between your thyroid and your stomach runs through Autoimmunity, through Autoimmune gastritis. A slow thyroid does slow the movement of your whole gut, as 'Your Thyroid and Your Gut' in 'How It All Connects' explains.

Stress. About a third of the acid released with a meal is triggered by your brain, through the sight, smell, and anticipation of food.

That signal travels down the vagus nerve, and it works best when your Nervous System is in rest-and-digest. A meal eaten in fight or flight starts with less of that first wave. 'How Stress Opens the Gut' in the stress chapter describes what else stress does to digestion.

Medications. Proton pump inhibitors and H2 blockers lower stomach acid by design. They have their own section below.

Heartburn: Too Much Acid, or Too Little?

Heartburn is the burning behind your breastbone when stomach contents rise into your esophagus. When reflux happens often enough to cause symptoms or damage, it is called gastroesophageal reflux disease, or GERD.

What conventional gastroenterology teaches. Reflux is mostly a problem of the barrier between your stomach and your esophagus.

• A ring of muscle called the lower esophageal sphincter, or LES, sits at the top of your stomach, supported by your diaphragm. It is meant to open for swallowing and stay closed the rest of the time.
• Everyone has brief moments when the LES relaxes on its own, called transient relaxations. They are the main way reflux happens, in healthy people and in people with GERD alike. In GERD, those moments more often carry acid upward.
• A hiatal hernia, where part of the stomach slides up through the diaphragm, weakens the barrier further.
• Symptoms can come from weakly acidic or even non-acidic reflux, which specialized testing can now detect.

What many Functional Medicine practitioners teach. Dr. Kharrazian, and Dr. Jonathan Wright and Dr. Lane Lenard in their book Why Stomach Acid Is Good for You, describe a different pattern they see in practice. When acid runs low, food is broken down slowly and sits longer, and pressure and fermentation can push contents upward.

In their view, the burn can feel identical while the stomach underneath makes too little acid.

This view has not been tested in controlled trials. What research does show is that low-acid stomachs are often uncomfortable: in the Autoimmune gastritis study above, a heavy, overfull feeling after meals was the most common complaint.

For so many of the Women I work with, the heartburn, the reflux, the chronic indigestion that has followed them for years is coming from too little stomach acid, when everyone assumed it was too much.

Both patterns are real, and you cannot tell them apart by how the burn feels. That is the reason for testing before anyone commits you to years of treatment in either direction.

Midlife hormones play a part too. In the Nurses' Health Study of more than 51,000 postmenopausal Women, hormone therapy users reported more reflux, and the risk rose with estrogen dose and duration.

This was observational research from an era when most hormone therapy was taken by mouth. If reflux begins or worsens after you start hormone therapy, tell your prescriber, and keep every dose change in that conversation.

What the American College of Gastroenterology suggests for reflux:

• Avoid eating within 2 to 3 hours of bedtime.
• Raise the head of your bed if symptoms come at night.
• Notice and avoid your own trigger foods.
• Avoid tobacco.
• Lose weight if you are carrying extra.

Some symptoms need a doctor promptly, before any home experiment. The same guideline advises an endoscopy as soon as feasible for reflux with trouble swallowing, weight loss you cannot explain, bleeding, vomiting, or anemia. Chest pain or pressure can be your heart, and it needs emergency care first.

PPIs: When They Are Needed, and What Long-Term Use Can Cost

Proton pump inhibitors, or PPIs, turn down the acid pumps in your parietal cells. Omeprazole (Prilosec), esomeprazole (Nexium), lansoprazole (Prevacid), and pantoprazole (Protonix) are common examples.

A 2023 review of studies from 23 countries estimated that nearly 1 in 4 adults uses a PPI. More than half of users were Women, about 1 in 4 users stayed on them longer than a year, and more than a quarter of those stayed longer than 3 years.

When PPIs are truly needed. For many conditions, a PPI is the right and necessary medication, and gastroenterology guidelines are clear about them:

• Healing erosive esophagitis, and keeping it healed.
• Complicated reflux, such as an esophageal ulcer or a narrowing called a stricture.
• Barrett's esophagus.
• Eosinophilic esophagitis.
• Healing stomach and duodenal ulcers, and as part of H. pylori treatment.
• Protecting a Woman at high risk of bleeding from the upper digestive tract.
• Rare conditions in which the stomach makes far too much acid.

The American Gastroenterological Association advises that people with complicated reflux, Barrett's esophagus, eosinophilic esophagitis, or a high risk of upper GI bleeding generally stay on their PPI. If this is you, your PPI is protecting you, and it belongs in your plan.

When the question is worth asking. Many Women start a PPI for heartburn and simply keep taking it. The American College of Gastroenterology recommends an 8-week trial for classic reflux, and when symptoms respond, an attempt to stop.

The American Gastroenterological Association advises that everyone on a PPI have the reason for it reviewed regularly, and that anyone without a clear ongoing reason be considered for a trial off it.

What long-term use has been linked to. Most of this research is observational, meaning it shows a link without proving the PPI caused the problem.

• B12. In a study of about 26,000 people with B12 deficiency, 2 or more years of PPI use carried 65 percent higher odds of deficiency.
• Iron. In a study of about 77,000 people with iron deficiency, 2 or more years of PPI use carried about 2.5 times the odds. The risk was higher at higher doses, and it fell after the medication was stopped.
• Magnesium. In 2011 the FDA warned that long-term PPI use can cause low magnesium, most often after more than a year. In about 1 in 4 of the cases it reviewed, magnesium supplements alone did not correct it and the PPI had to be stopped.
• Fractures. In 2010 the FDA warned of a higher risk of hip, wrist, and spine fractures with high doses or use of a year or longer, as 'What Thins Bone' in the Bones chapter describes.
• C. difficile. In 2012 the FDA warned that PPIs may raise the risk of C. difficile diarrhea, and advised anyone on a PPI with diarrhea that does not improve to seek care promptly.
• SIBO. A 2013 analysis found about twice the odds of small intestinal bacterial overgrowth in PPI users, with the link clearest in studies using the most accurate test.
• Thyroid medication. Levothyroxine tablets need stomach acid to dissolve, as 'Medication Timing: What Blocks Absorption' in the Thyroid chapter explains.

The American Gastroenterological Association's 2022 update adds 1 more point. The decision to stop a PPI should rest on whether you still need it. A possible side effect, on its own, does not settle that question.

Monitoring your B12, ferritin, and magnesium lets you and your prescriber watch for these effects while you take it.

Coming off, only with your prescriber. Stopping a PPI suddenly can bring a rebound surge of acid. In a trial of 120 healthy volunteers with no reflux at all, 44 percent developed heartburn or acid symptoms after stopping 8 weeks of a PPI, compared with 15 percent on placebo.

The rebound can feel like proof you need the medication. It is usually temporary, as your stomach readjusts. Your prescriber may taper the dose or stop it outright, and either way, the plan is theirs to make with you.

My Own Low Stomach Acid, and the Symptoms I Never Had

I had low stomach acid, and I had no symptoms of it at all. No heartburn, no heaviness I noticed, nothing that would have sent me looking.

What I had were labs. My early testing showed I was extremely nutrient deficient in literally everything, even though I was eating what I believed was a very healthy diet.

As I treated my stomach with digestive enzymes and betaine HCl, my body was able to absorb my nutrients again. Both my Functional Medicine practitioners and the educators in the Hashimoto 411 group helped me understand my low stomach acid and how to remedy it.

A quiet stomach can still be a low-acid stomach. If your nutrients stay low no matter how well you eat, the symptom lists in this chapter may never describe you, and the testing still belongs on your list.

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Around my meals today, I take Atrantil and Designs for Health Digestzymes before I eat, with 2 or 3 capsules of Nutricost Betaine HCl + Pepsin, and BodyBio Sodium Butyrate when I am done. Digestzymes carries 200 mg of betaine HCl per capsule of its own, so the betaine adds up across the 2 products. 'What I Take, and Why', in the Supplements chapter, lists the rest of my routine and the reason for each.

How You Eat Is Part of How You Digest

Before any capsule, there is the meal itself.

• Sit down. Your stomach begins making acid when you see and smell food, and that first wave depends on your Nervous System feeling safe enough to digest.
• Take 1 breath first: inhale deep, exhale long. Diaphragmatic belly breathing regulates the Nervous System, and a regulated Nervous System digests.
• Chew until the texture is gone. Every chew gives acid and pepsin more surface to work on. 1 of the Hashimoto 411 educators reminds Women to chew something alongside a smoothie, because chewing is how digestion starts, and a meal swallowed in a few gulps skips much of that signal.
• Sip at meals. Many Functional Medicine practitioners suggest small sips of water with food over large glasses. Research on whether water dilutes stomach acid is thin, so notice what your body prefers.
• Leave space. 4 to 5 hours between meals lets your gut do its housekeeping, as 'Give Your Gut Time to Rest Between Meals' in the next chapter explains, and finishing 2 to 3 hours before bed eases nighttime reflux.

The same salmon eaten at a table, slowly, arrives in a stomach that is ready for it. 'The Vagus Nerve and the Gut-Brain Axis' in the stress chapter explains the wiring.