Hypochlorhydria describes the condition of insufficient hydrochloric acid in the stomach. Whereas acid hyper-secretion is a recognised problem this book talks about, some people have problems from natural hypochlorhydria - producing too little acid. But high dose acid suppressant medication can also result in too little stomach acid - a result of the medicine being too good at its job.
Stomach acid is required to leach essential minerals and vitamins from foods to be better absorbed in the intestines, trigger the production of pepsin and other enzymes and fight unwanted bacteria.
In the stomach, the hydrochloric acid leeches essential minerals and vitamins from foods. To enable their uptake in the duodenum, they are chemically converted to more easily assimilated chlorides.
Hypochlorhydria can result in low vitamin B12 and anaemia through insufficient uptake of iron, hypocalcaemia and exacerbation of osteoporosis through insufficient uptake of calcium, hypomagnesaemia through insufficient uptake of magnesium etc. [c-v]
Another role of stomach acid is to kill unwanted bacteria so hypochlorhydria may result in greater incidence of infections like C-Difficile.
In USA where PPIs have been readily available over the counter for years and widely advertised on television, this has been a problem which led to the FDA issuing warnings against overuse of PPIs. These are powerful drugs whose use should always be monitored by a doctor to ensure they are used properly at the lowest effective dose. Studies have shown "Patients receiving prescription PPI from a GI are more likely to be optimal users with better symptom control. Conversely, consumers are more likely to be suboptimal users with inadequate symptom control." [c-vi]
The FDA warnings have scared many people away from using PPIs to trying "natural" therapies instead.
The hypochlorhydria "side effects", however, have been blown out of proportion. Most patients on minimally effective dose shouldn't experience them. Those taking high dose acid suppressant medication for years, however, should have their mineral levels checked by regular blood tests and supplemental minerals may be prescribed. (N.B. prescription of these supplements is required to get the correct dose and formulation. e.g. Calcium Citrate is required to boost calcium levels rather than the cheaper and more readily available calcium carbonate which will only react with remaining stomach acid to lower it further.)
A paper produced in March 2017 [c-vii] provides 10 best practice advice notes including not to take PPI long term for acid reflux alone but that patients with Barrett's Oesophagus should remain on PPIs.