Human stomach gas problem concept. 3d illustration

Understanding the Importance of Stomach Acid

By Ross Pelton, RPh, PhD, CCN
Scientific Director, Essential Formulas

Stomach or gastric acid is a critical component of the human immune system. It is an essential defense mechanism protecting us against invading pathogens such as viruses, bacteria, and parasites. Unfortunately, many people don’t understand or appreciate the crucial functions of stomach acid.

Relative levels of acidity and alkalinity are measured on a logarithmic scale known as pH. The pH scale goes from 0 to 14. A pH 7 is neutral, whereas below seven is increasingly acidic and above seven is increasingly alkaline. Every single digit on a logarithmic scale represents a ten-fold change. Thus, a pH of 4 is ten times less acidic than a pH of 3, and a pH o 5 is 100 times less acidic than a pH of 3.

The function of Stomach Acid

Stomach acid is produced by cells in the stomach lining named parietal glands, which secrete hydrochloric acid (HCl). HCl is a powerful acid. One of the primary functions of stomach acid is to act as a barrier that prevents bacteria, viruses, and parasites from entering the body. They are killed by stomach acid before entering the small intestines and being absorbed into the body. Cells in the wall of the stomach also secrete a compound named pepsinogen. Another critical function of stomach HCL is converting pepsinogen into pepsin, an essential protein-digesting enzyme. A low level of acidity also contributes to reduced absorption of essential nutrients such as calcium, magnesium, iron, vitamin B12, vitamin B6, and folic acid.

Comparing Stomach vs. Intestinal Acidity

The average pH in the empty stomach is generally around 1 to 2, which is highly acidic. The pH throughout the small and large intestines varies somewhat, but on average, the pH in the intermediate level of acidity in the intestines is a pH of about 6.

So, what’s the difference between the acidity in the stomach compared to the intestinal tract. Going from a pH of 2 to 6 is a 4-point change on the logarithmic H scale. Since each point represents a factor of ten, a 4-point change goes from 1 to 10, 100, 1,000, 10,000. Thus, the stomach’s acidity is approximately 10,000 more acidic than the pH throughout the rest of the intestinal tract.

Stomach Acid & Immunity

Stomach acid is so highly acidic; it kills organisms that come into contact with it. This explains why your stomach acid is such a critical part of your immune system. If you have proper acidity levels, most ingested bacteria, viruses, and parasites get killed in the stomach very quickly. Thus, your stomach acid is a frontline defense against most significant pathogens that people ingest in food, water, or anything else that enters your mouth, including things like kids playing in the dirt and then putting their fingers in their mouth.

Hypochlorhydria (Low Stomach Acid)

Stomach acid is produced by cells in the stomach lining called parietal cells, which secrete hydrochloric acid (HCl). Typical stomach acidity is pH of 1 to 2. Hypochlorhydria or low stomach acidity is pH of 3 to 5. Stomach acidity is five or above is classified as achlorhydria or lack of stomach acidity.  A normal pH of 2 too low, stomach acid at pH four is 100x less acidic; from ph2 to hypochlorhydria at pH 5 = 1,000 x less acidic.

Symptoms of Low Stomach Acid:

Heartburn and gastroesophageal reflux disease (commonly known as GERD) are often mistakenly caused by too much stomach acid. The opposite is true. These conditions are usually the result of too little stomach. The pain that if frequently experienced is due to inflammation in the lining of the stomach. The name for this condition is gastritis, which is a prevalent cause of both pain and a low level of stomach acid. Other symptoms of low stomach acid include gas, bloating, upset stomach, nausea, indigestion, undigested food in stools, nutritional deficiencies of iron, vitamin B12, calcium, and magnesium.

Causes of Low Stomach Acid:

The production of hydrochloric acid from the parietal cells in the stomach lining generally declines with age.i Another common cause of low stomach acid is being infected with Helicobacter pylori or H. pylori. in addition to low stomach acid, this infection also frequently causes stomach ulcers. The use of drugs that neutralize or suppress stomach acid is another frequent cause of low stomach acid levels.

Prevalence of Low Stomach Acid

Low stomach acid is more common in older adults because the stomach lining thins with age, and older adults also have a greater incidence of H. pylori infection.ii Studies reporting the prevalence of low stomach acid vary widely, ranging from a low of 10%. Some studies reported the prevalence of gastritis in elderly patients to be as high as 78.8%.iii,iv

Acid-Suppressing Drugs

Millions of people take antacids and acid-suppressing drugs such as H2-blockers and proton pump inhibitors (PPIs) to treat the pain and discomfort associated with indigestion, heartburn, or acid reflux. However, stomach pain is often caused by an inflammation in the stomach lining, known as gastritis, which is frequently due to infection with the bacterium known as Helicobacter pylori or H. pylori. If stomach pain is caused by H. pylori infection, suppressing the pain with acid-suppressing drugs is the WRONG thing to do because H. pylori thrive in a more alkaline environment.

People take these drugs to suppress the production of stomach acid or neutralize it. In either case, reducing the level of stomach acid increases gastric pH levels. Let’s say this changes the stomach pH from 2 up to a group of 4. Moving the pH up two points means the contents in the stomach are now 100 times LESS acidic than average. This means any ingested pathogens have a much better chance of surviving passage through the stomach and arriving in the intestinal tract alive and capable of initiating an infection.

It is disturbing that the use of these drugs is increasing. In a study that reported trends in prescription drug use in the United States, when the use of PPIs from 1999-2000 was compared with PPI use during 2011-2012, American’s use of PPI drugs in the U.S. nearly doubled, from 3.9% up to 7.8%.v

How to Test Your Stomach Acid Levels

Hydrochloric acid (HCL) tablets are available as a dietary supplement under betaine hydrochloride, which is made from beets. Functional medicine physicians frequently recommend purchasing HCL capsules that also contain pepsin. If you are not producing enough HCL, you are probably not having enough of the protein-digesting enzyme pepsin.

The purpose of this test is to determine if you have enough HCL and pepsin being produced in your stomach to digest the proteins in a protein-containing meal. To conduct this test, start out taking one capsule at the beginning of a protein-containing meal. Do this for two days in a row. If you don’t notice anything, increase the dose to two HCL/pepsin capsules at the beginning of protein-containing meals. If you still don’t see anything, continue increasing the amount, one tablet at a time. At some point, you will notice a mild burning/acidic sensation in your stomach. At this point, decrease the dose to the previous number of capsules you took that did not cause any discomfort. Many people, especially elderly individuals, need to take 6 or 7 capsules with their protein-containing meals.

NOTE: Hydrochloric acid capsules should not be taken, and this test should never be performed by individuals who are taking any anti-inflammatory medication such as aspirin, ibuprofen (Motrin or Advil), or Indocin, or other NSAIDs.

Closing Comments:

Maintaining normal levels of stomach acid in the range of pH 2-3 is vital for two reasons. First, stomach acid is a critical first line of defense for your immune system. This robust acid environment prevents viral, bacterial, and parasite pathogens from gaining entry into your body. Also, low levels of stomach acid and pepsin can result in protein maldigestion and reduced absorption of essential vitamins and minerals.

Suppose you are having stomach pain or discomfort. In that case, it is advisable to check with your physician rather than taking readily available acid-suppressing medications which suppress symptoms but do not address the cause of the problem.


i Britton E and McLaughlin JT. Aging and the gut. Proceedings of the Nutritional Society. 2013;72:173-177.
ii Wyatt JI, et al. Helicobacter pylori, gastritis, and peptic ulceration in the elderly. J Clin Pathol. 1992 Dec;45(12):1070-4.
iii Hurwitz A, et al. Gastric acidity in older adults. JAMA. 1997 Aug 27;278(8):659-62.
iv Feyisa ZT and Woldeamanuel BT. Prevalence and associated risk factors of gastritis among patients visiting Saint Paul Hospital Millennium Medical College, Addis Ababa, Ethiopia. PLOS ONE. 2021 Feb 9;16(2):e0246619.
v Kantor ED, et al. Trends in Prescription Drug Use Among Adults in the United States From 1999-2012. JAMA. 2015;314(17):1818-1830.