The thought of stomach acid, for many, no doubt evokes memories of spicy meals or having eaten too much. Maybe the occasional episode of heart burn and for many the terms acid reflux and GERD (gastroesophageal reflux disease) will come to mind. Another word that tends to crop up time and time again is ‘excess’. It’s easy to see why. Walk into any pharmacy or supermarket and you can easily find scores of over-the-counter medicines and remedies to help soothe away or block excess stomach acid. TV commercials promoting such products are rife, so it’s little wonder that the assumption that digestive issues are all to do with excess acid is a commonly held belief. But what about low stomach acid? Never heard of it? You’re not alone. Surprisingly, low stomach acid (hypochlorhydria) is a common occurrence, much more common in fact than excess stomach acid. Indeed, it may be that the vast majority of people who believe they are suffering from ‘excess’ stomach acid are really actually suffering from the opposite. This, at first, might seem hard to swallow but let’s take a look at the evidence.
Excess stomach acid
First, let’s take a look at conditions related to excess stomach acid just to put things into perspective. Below is a table listing hypersecretory (excess stomach acid) conditions, taken from a 2009 paper (1) I then searched the internet looking for how common these conditions are.
|Condition||How common is it?||Notes|
|Zollinger-Ellison syndrome||0.1-3 cases per million patients per year (2)|
|Antral G cell hyperplasia/hyperfunction||Listed as very rare (3)|
|Helicobacter Pylori infection||Extremely common||H.Pylori infection can just as easily cause a lack of acid, too|
|Gastric Outlet obstruction||Around 5% of people with peptic ulcer disease. 2000 operations in the US per year (4)|
|Short-bowel syndrome||Around 2 in every million have this condition (5)|
|Retained gastric antrum syndrome||Difficult to find numbers, stated as very rare (3)||Seems to be a rare condition following gastric surgery in the first half of the 20th century (6)|
|Chronic renal failure||~350 per million (7)||Also known as end-stage renal disease|
|Cysteamine treatment in children with cystinosis||Extremely rare, 15 cases of cystinosis in the US per year||Genetic disorder|
|Systemic mastocytosis||Extremely rare (8)|
|Basophilic granulocytic leukemia||~6000 cases in the US in 2014 (9)||Equated with chronic myeloid leukemia|
|Idiopathic hypersecretion||Seems to be a defunct term as our understanding has progressed|
|Associated with non-gastrin secreting tumor (non-ZES tumour)||Difficult to find accurate numbers for||Stomach cancers are quite common in certain populations though|
|Rebound hypersecretion||Common||Caused when acid blocking medication is stopped|
|Possible association with gastric hypersecretory states a. Hypertrophic, hypersecretory gastropathy b. Associated with stress c. Associated with head lesions d. Cystic fibrosis||a. related to H.Pylori d. from 1 in 377 to 1 in 90,000 depending on the population||b. It’s unclear what type of stress is meant though possible stress induced gastritis (10) c. Little data available|
As you can see from the table most conditions related to excess stomach acid are, fortunately, rare and probably the last thing you would want to be doing if you were suffering from any of these conditions is self-medicating with acid blocking medication or antacids. So if excess stomach acid is indeed an uncommon thing, often caused by very unpleasant conditions, why does the idea of excess acid persist? Well, that is the subject of another post. For now, just make a note of H.Pylori and rebound hypersecretion in the above table and let’s have a look at stomach acid and what a lack of it can mean.
What does stomach acid do?
Stomach acid performs two important functions; the sterilisation of the stomach and anything that enters and the breaking down of foods and helping with absorption of nutrients. Both of these things are vital to our wellbeing and a reduction in stomach acid can and will severely compromise both. There are essentially four outcomes from having low stomach acid
- Reduced ability to absorb nutrients
- An increased chance of bacterial overgrowth
- A decreased resistance to infection brought about by the above two factors
- An increased risk of cancer and other diseases
I would hope you would agree that any one of these things are pretty serious conditions so let’s dig a little deeper.
Malabsorption of Nutrients
Stomach acid is essential for breaking down proteins and liberating nutrients from food. Hydrochloric acid converts pepsinogen into pepsin; one of the enzymes responsible for the breakdown of protein into peptides and amino acids. Pepsin works best in a strongly acid environment. Gelatinase, an often overlooked enzyme, requires an acidic environment to break down collagen, too. With low levels of acid, or in cases with no stomach acid (achlorhydria), protein will not be digested as quickly or as properly as it should be. This can explain the ‘heavy’ feeling that some people have after eating meat. A lack of stomach acid will allow the meat to ‘sit’ in your stomach, and the stomach will take much longer to empty as a result. It’s worth noting at this point that though protein digestion begins in the stomach it’s actually completed in small intestine and I’ll take a closer look at that in the future.
Studies have shown that people with low or no stomach acid fail to absorb other nutrients properly, too. One study showed that both Helicobacter Pylori infection (which suppresses stomach acid) and acid suppression using the drug omeprazole reduced the bioavailability of vitamin C (11). Studies have also linked low stomach acid to the malabsorption of beta-carotene (a vitamin A precursor); (12), zinc (13), (14), (15), iron (16), vitamin B12, (17), (18), (19), folate (20), (21). Research also suggests that low stomach acid adversely affects the absorption of magnesium (22) and possibly calcium, though studies on calcium tend to be inconclusive with some stating a link and others claiming no link. Though, those claiming no link tend to be short term studies using acid blocking drugs.
Increased Chance of Enteric Infections
As one of the main functions of stomach acid is to destroy incoming pathogens it’s perhaps unsurprising that a loss or reduction of acid greatly increases the chance of enteric (intestinal) infections. In laboratory experiments it was demonstrated that the common pathogenic micro-organisms Escherichia coli (strains c690 and K-12), Helicobacter pylori, Klebsiella, Salmonella, Shigella flexneri, Proteus, Enterobacter, Enterococcus faecalis, Enterococcus faecium, Staphylococcus epidermidis, Staphylococcus aureus and Candida albicans, did not survive at pH 1.0 or 2.0 (a healthy human gastric pH), but at pH 4.0 -hypochlorhydria is defined as having a gastric pH between 4 and 7- all micro-organisms survived (23), however, this was in an in vitro acid only environment.
In a 2011 systematic review looking at the use of proton pump inhibitors (drugs used to block the production of acid) and increased susceptibility to enteric infections the report authors wrote
“The use of PPIs increases gastric pH, encourages growth of the gut microflora, increases bacterial translocation and alters various immunomodulatory and anti-inflammatory effects. Enteric pathogens show variable gastric acid pH susceptibility and acid tolerance levels. By multiple mechanisms, PPIs appear to increase susceptibility to the following bacterial enteropathogens: Salmonella, Campylobacter jejuni, invasive strains of Escherichia coli, vegetative cells of Clostridium difficile, Vibrio cholerae and Listeria. We describe the available evidence for enhanced susceptibility to enteric infection caused by Salmonella, Campylobacter and C. difficile by PPI use, with adjusted relative risk ranges of 4.2–8.3 (two studies); 3.5–11.7 (four studies); and 1.2–5.0 (17 of 27 studies) for the three respective organisms.” (24)
What this means is that medications that blocked stomach acid production made it easier for pathogenic bacteria to gain a foothold in the stomach as there wasn’t enough acid to effectively kill them.
Small Intestine Bacterial Overgrowth
Small intestine bacterial overgrowth, usually shortened to SIBO, is a complex disorder that can arise from many different conditions (27). As the name suggests it results from having too many bacteria in the small intestine. Low stomach acid (pH above 4) allows bacteria to pass through the stomach and into the small intestine.
Acid also plays another very important role when it comes to the small intestine. When chyme enters the small intestine from the stomach it should be highly acidic. This acidity is required to turn the prohormone prosecretin into its active form secretin.
Secretin performs a number of important functions which include increasing the pH of the small intestine and increasing the potency of cholecystokinin, a hormone which amongst other things stimulates the release of digestive enzymes in the small intestine. If the chyme isn’t sufficiently acidic then the secretin/cholecystokinin response will be diminished.
Atrophic gastritis is a condition in which the stomach loses the parietal cells; the cells that it needs to produce acid. There are two primary types of atrophic gastritis; H.Pylori infection and autoimmune gastritis (though H.Pylori has also been suggested as a cause of this variant, too (28).) Loss of the ability to secrete acid leads to a condition known as hypergastrinemia which can, over time, lead to cancer. Note: hypergastrinemia can also be caused by PPI use (29) and certain types of cancer, too.
Low stomach acid can also spell problems for vitamin C, which is actively released into the stomach. Vitamin C, otherwise known as ascorbic acid, prefers an acidic environment. Above a pH of 4 it can undergo an irreversible reaction to form 2,3-diketogulonic acid, which can’t be used by the body and so is excreted (30). Why is this important? Vitamin C inhibits the formation of carcinogenic N-nitroso compounds within gastric juice.
Another study found that acid suppressing medication which led to microbial overgrowth in turn led to alcohol being converted to the carcinogen acetaldehyde within the gut (microbial overgrowth can also produce ethanol in the gut through fermentation.) (31)
As mentioned above, teasing out the evidence of whether low stomach acid leads to poor calcium absorption and in turn diseases like osteoporosis is difficult. In an comprehensive review entitled
Gastric Acid, Calcium Absorption, and Their Impact on Bone Health the authors write
“…it is experimentally difficult to unmask the potential correlation between a reduction in gastric acidity and calcium absorption, given our body’s high capacity for compensation. In addition, slight alterations in mineral homeostasis may take years to manifest themselves clinically, for example, in osteopenia or fractures. Without following up on test subjects on a long-term basis, snapshot measurements which may still lie within clinically normal range can be misleading.”
They go on to conclude
“In summary, it should be noted that the stomach secretes not only acid, but also hormones that have been shown to directly alter calcium and/or bone homeostasis. The secretion of these hormones depends on the neuroendocrine machinery that also regulates acid secretion. It is therefore plausible that the correlation between states of impaired acid secretion and impaired bone mineralization is multifactorial by depending on intragastric pH and serum levels of gastric hormones.”
A 2010 review paper looking at antacid medications and their role in food allergies concluded that in addition to current warnings about antacid medications
“….to this list, we suggest that ‘Increased risk for sensitization against dietary proteins’ and ‘Lowering the food allergens levels needed to elicit hypersensitivity reactions in food-allergic patients’ should be added. Therefore, we question over-the-counter sale of anti-ulcer drugs and suggest prescribing them according to strict indications during a therapeutically useful period of time, especially during pregnancy.” (32)
They found that proteins that were incompletely digested due to lack of acid and lack of stimulation of secretin (see above) provoked an immune response which led to allergy. The use of aluminium compounds in some medications also appeared to act as an immunostimulant.
Perhaps most shocking of all they found evidence that pregnant mothers who take acid blocking medication developed allergic responses that were passed on to the unborn baby! The cited study also appeared to show a link between in utero exposure to antacid medication and the development of childhood asthma (33).
Gastroesophageal Reflux Disorder
Gastroesophageal reflux disorder or GERD for short is so often attributed to excess acid, and whilst it may certainly be present in such cases the vast majority of cases are caused by a lack of stomach acid not an excess. At a later date I will take a closer look at GERD and low stomach acid.
Helicobacter Pylori and PPIs
Time and time again these two keep popping as key factors in low stomach acid, one by design and one via evolution. With PPI’s the very notion that eliminating stomach acid- an integral part of our biology for hundreds of millions of years (that is, a mechanism from our earliest forms)- almost completely and for years on end seems like utter lunacy. Many of the studies referenced in this article directly involve the use of PPIs either as an experimental tool or causative agent in disorders and illnesses. There may be a few cases in which it is a good idea to take these substances but the evidences suggests that they are over prescribed by doctors or misused as an over the counter medicine. In future posts I’ll be looking at this truly bizarre practice and what the alternatives are.
For H.Pylori, the issue is perhaps more complicated, even now as study after study implicates this bacteria in disease states there seems to be much we still don’t know, though I’ll be taking a look at this in future posts, specifically how and why it alters stomach acid production and what to do about it.
All in all we may need to rethink the idea of excess stomach acid and come to a better understanding of just what goes on in the stomach and how essential stomach acid is. You might want to think twice before you reach for those stomach acid medications.