Low Stomach Acid – Fact or Fiction?
Low Stomach Acid – Fact or Fiction?

Low Stomach Acid – Fact or Fiction?

By Liz Kenyon, Physiology Assistant

Stomach acid plays two important roles in our body: initiating the breakdown of our food into absorbable components for energy and nutrition, and it helps protect us from infection by killing potentially harmful microbes and spores in food1,2.

Acidity levels are measured on what’s known as a pH scale from 1 to 14, with 1 being the most acidic, 7 being neutral i.e., water, and 8 or above being alkaline. Stomach acid levels are defined as being too low when the pH of the stomach rises above 4, which has the medical term hypochlorhydria. Complete loss of stomach acid production is called achlorhydria.

There is currently little literature available on low stomach acid, however, we know some things that can cause it:

  • Taking proton pump inhibitors (PPIs)- commonly used drugs for acid reflux that prevent acid production e.g. omeprazole, esomeprazole, lansoprazole, etc3.
  • Autoimmune gastritis- a disease where the immune system destroys acid producing cells in the stomach called parietal cells4.
  • Helicobacter pylori (H. pylori) infection- this bacteria colonises the stomach and makes an enzyme that neutralises acid. However, acidity levels usually restore after the initial infection period 5. Here, at the functional gut clinic we can test for H. pylori using a simple breath test kit.

Also, there is a frequent observation that those with a disease called Hashimoto’s thyroiditis (where the immune system attacks the thyroid) have low stomach acid. This can be explained by the association between Hashimoto’s thyroiditis and autoimmune gastritis, a cause of low stomach acid. In turn autoimmune gastritis is also linked to pernicious anaemia (vitamin B12 deficiency) as the parietal cells are destroyed. In the stomach, parietal cells produce something called ‘intrinsic factor’ which is essential for the absorption of vitamin B12 10,11. Therefore, leading to B12 deficiency.

Stomach acid is an important part of gut physiology. It aids the digestion process because many digestive enzymes, such as pepsin, are most active in low pH. Therefore, having low stomach acid may put at risk of inefficient digestion and nutritional deficiencies. In addition, stomach acid’s microbe killing abilities mean that by having low stomach acid, there is an increased risk of intestinal infections but also increased survival of bacteria in the upper small bowel. This can lead to small intestinal bacterial overgrowth (SIBO), an unpleasant condition characterised by bloating, abdominal pain, and nausea due to gas produced by the overgrown bacteria6. In fact, long-term PPI use is associated with an increased risk of SIBO7. However, it should be noted that low stomach acid is not a leading cause of SIBO. The Functional Gut Clinic can test for SIBO using simple, at home breath test kits.

Online, there are claims that low stomach acid is an explanation for gastrointestinal problems. One disease claimed to be caused by low stomach acid is gastro-oesophageal reflux disease (GORD). GORD is a real disease that occurs when stomach acid flows back into your food pipe (oesophagus) giving a rise to troublesome symptoms including heartburn and regurgitation. Most people experience reflux at some point, especially after a large or spicy meal, but people with GORD have more reflux than normal and this leads to troublesome symptoms and complications. The treatment for GORD is usually PPIs and over the counter antacids. These are important medications because long-term acid exposure in the oesophagus increases the risk of oesophageal adenocarcinoma, a form of cancer.

Having GORD and being on these therapies could lead to low stomach acid. However, low stomach acid is not the cause of GORD. One claim made is that low stomach acidity increases intra-abdominal pressure, causing the opening from the food pipe to the stomach to open, allowing acid reflux to occur. There is no scientific evidence to support these claims so if you are experiencing frequent reflux or are worried about low stomach acid, we suggest you contact your doctor. At the Functional Gut Clinic, we offer pH monitoring, which can diagnose GORD and also help to identify those with low stomach acid by placing a pH sensor into the stomach.

Treatment for low stomach acid is difficult as there is no gold standard therapy. Some patients can reduce their dose of PPIs but for others this is not an option. Apple cider vinegar (ACV) is a cure stated by some people online, as ACV has a similar pH to stomach acid of around 2.5. However, ACV does have proven side effects including oesophageal injury meaning this is a likely unsafe treatment method8. Another reported therapy for low stomach acid is hydrochloric (HCl) acid tablets. The theory is that, as hydrochloric acid is the resident acid in the stomach, supplementing HCl will increase acid levels. One study on this looks promising, however, it was performed in healthy volunteers (with medically induced low gastric acid) so more studies on real patients are necessary before we can make any assumptions 9.

In conclusion, low stomach acid can lead to nutrient deficiencies and increased risk of intestinal infections, such as SIBO, due to stomach acid’s roles in digestion and killing microbes. Low stomach acid is difficult to diagnose and treat due to the little knowledge we have on it. There is a lot of misinformation on the internet about low stomach acid, meaning that it can be easy to think that low stomach acid is the cause of many health problems. If you are concerned about having low stomach acid or have any troublesome digestive issues, be sure to contact your GP.


  1. Kim, T. and Shivdasani, R.A. (2016). Stomach development, stem cells and disease. Development, 143(4): 554-565
  2. Hunt, R.H., Camilleri, M., Crowe, S.E., El-Omar, E.M., Fox, J.G., Kuipers, E.J., Malfertheiner, P., McColl, K.E.L., Pritchard, D.M., Rugge, M., Sonnenberg, A., Sugano, K. and Tack, J. (2015). The stomach in health and disease. Gut, 64(10): 1650-1668
  3. Lee, L., Ramos-Alvarez, I., Ito, T. and Jensen, R.T. (2019). Insights into effects/risks of chronic hypergastinemia and lifelong PPI treatment in man based on studies of patients with Zollinger-ellison syndrome. International Journal of Molecular Sciences, 20(20): 5128
  4. Neumann, W.L., Coss, E., Rugge, M. and Genta, R.M. (2013). Autoimmune atrophic gastritis- pathogenesis, pathology and management. Nature Reviews Gastroenterology and Hepatology, 10(9): 529-541
  5. Waldum, H.L., Kleveland, P.M. and Sordal, O.F. (2016). Helicobacteri Pylori and gastric acid: an intimate and reciprocal relationship, 9(6): 836-844
  6. Pimentel, M., Saad, R.J., Long, M.D., Rao, S.S.C (2020). ACG Clinical Guideline: Small Intestinal Bacterial Overgrowth. The American Journal of Gastroenterology, 115(2): 165-178
  7. Su T, Lai S, Lee A, He X, Chen S. Meta-analysis: proton pump inhibitors moderately increase the risk of small intestinal bacterial overgrowth. J Gastroenterol. 2018 Jan;53(1):27-36
  8. Peloso, E. (2016). Apple cider vinegar for diabetes: Limited evidence, potential risks. Pharmacy today, 22(2): 18
  9. Yago, M.A.R., Frymoyer, A.R., Smelick, G.S., Frassetto, L.A., Budha, N.R., Ware, J.A. and Benet, L.Z. (2014). Gastric Re-acidification with Betaine HCl in Healthy Volunteers with Rabrazole-Induced Hypochlorhydria. Molecular pharmaceutics, 10(11): 4032-4037
  10. Collins, A.B. and Pawlak, R. (2016). Prevalence of vitamin B-12 deficiency among patients with thyroid dysfunction. Asia Pacific Journal of Clinical Nutrition, 25(2): 221-226
  11. Toh, B. (2017). Pathophysiology and laboratory diagnosis of pernicious anemia. Immunological Research, 65: 326-330