By Jordan Haworth, Clinical Physiologist
Stomach acid plays two important roles in your body: breaking down food and killing harmful microbes that you ingest1.
Acidity levels are measured by the pH scale from 1 to 14, with 1 being the most acidic, 7 being neutral, and 14 being the most alkaline.
The pH of stomach acid (hydrochloric acid) is around pH 1, which is as strong as battery acid. Although, gastric juice also contains water and mucus, so normal pH of the stomach is typically between pH 1.5 to pH 3.5,
Low stomach acid, also known medically as hypochlorhydria, is when the stomach does not produce enough acid to maintain a strong acidic environment.
Complete loss of stomach acid production is called achlorhydria.
It is also possible for the stomach to produce too much stomach acid. This is usually caused by the condition called Zollinger-ellison syndrome, where the body produces excess gastrin, the hormone required for stomach acid production2.
What causes low stomach acid?
The most common causes of low stomach acid (hypochlorhydria) are:
- Proton pump inhibitors (PPIs) – medications used for the treatment of heartburn and acid reflux that work by blocking stomach acid production e.g. omeprazole, esomeprazole, lansoprazole, etc3.
- Helicobacter pylori (H. pylori) – a type of bacteria which survives in the stomach by secreting an enzyme that neutralises stomach acid. H. pylori infection causes gastritis, which leads to less stomach acid production4.
- Autoimmune gastritis – an autoimmune disease where the immune system destroys the acid producing cells in the stomach called parietal cells5. This can also lead to vitamin B12 deficiency, or pernicious anaemia.
- Thyroid issues – low stomach acid is common in both hypothyroidism and hyperthyroidism. Also, stomach acid is needed for the absorption of the thyroid medication, l-thyroxine6.
What are the symptoms of low stomach acid?
The most common symptoms of low stomach acid are discomfort in the stomach, bloating, belching and a feeling full quickly or feeling full for long periods after eating.
Low stomach acid may lead to poorer digestion of proteins because pepsin, the digestive enzyme which breaks down protein, is most active in acid at around pH 2.
Having low stomach acid puts you at an increased risk of intestinal infections like bacterial gastroenteritis (food poisoning) and small intestinal bacterial overgrowth (SIBO).
SIBO is characterised by symptoms of bloating, abdominal pain, and nausea due to excess gas produced by bacteria in the small bowel7. The Functional Gut Clinic can test for SIBO using simple, at home breath test kits.
Despite online claims, there is no evidence that low stomach acid causes reflux. The treatment for acid reflux and heartburn is PPIs, which lead to low stomach acid. People who have been taking PPIs for 6-months or longer are more likely to have troublesome bloating and SIBO8.
How to test for low stomach acid?
Symptoms of low stomach acid, such as bloating, fullness and nausea, overlap with many other conditions, such as functional dyspepsia, gastroparesis, and irritable bowel syndrome (IBS). Therefore, symptoms alone cannot diagnose low stomach acid.
To diagnose low stomach acid, you need to measure gastric acid output. To do this, a capsule or probe with a pH sensor is placed into the stomach. Then a standardised meal is given, such as a nutrient drink. This will buffer the acid levels in the stomach. Then we time how long it takes for your stomach to reacidify after the meal.
The baking soda test for low stomach acid has no evidence to show it works. The theory is that baking soda (sodium bicarbonate) will react with stomach acid (hydrochloric acid) to produce gas (carbon dioxide) which will be belched. However, this may lead to a false positive or false negative diagnosis, especially since most belches are caused by how much air you swallow whilst drinking.
How to treat low stomach acid?
Apple cider vinegar (ACV) is claimed to be helpful since 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. Hydrochloric acid is naturally produced by the stomach, so supplementing HCl may help to decrease the pH of the stomach. One study on this looks promising, however, it was performed in healthy volunteers (with medically induced low gastric acid) so more studies on people with symptoms are necessary before we can make any recommendations9. It’s also unclear what amount of HCl supplementation is safe.
The most effective way of treating low stomach acid is to treat the underlying cause of low stomach acid. For example, stomach acid levels may return to normal after eradicating H. pylori infection.
Stopping PPIs will allow stomach acid levels to return to normal. If you are unsure whether you need PPIs, then it is important to consider testing for acid reflux complications, such as Barrett’s oesophagus, because these medications prevent damage to the oesophagus from acid, which if untreated, may increase your risk of oesophageal cancer10.
In conclusion, low stomach acid may 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 can be diagnosed with a gastric acid output test, but treatments are limited to treating the underlying cause. There is a lot of misinformation on the internet about low stomach acid, meaning that it can be easy blame to it as the cause of many health problems. If you want to test your stomach acid levels or speak to a doctor about digestive issues, then fill out a contact form on our website.
- 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
- Lee, L., Ramos-Alvarez, I., Ito, T. and Jensen, R.T. (2019). Insights into effects/risks of chronic hypergastrinemia and lifelong PPI treatment in man based on studies of patients with Zollinger-ellison syndrome. International Journal of Molecular Sciences, 20(20): 5128
- 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
- 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
- Virili, C., Bruno, G., Santaguida, M.G. et al. (2022). Levothyroxine treatment and gastric juice pH in humans: the proof of concept. Endocrine 77, 102–11
- 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
- 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
- Peloso, E. (2016). Apple cider vinegar for diabetes: Limited evidence, potential risks. Pharmacy today, 22(2): 18
- 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
- Jankowski JAZ, de Caestecker J, Love SB et al. Esomeprazole and aspirin in Barrett’s oesophagus (AspECT): a randomised factorial trial. Lancet 2018;392:400–8.