Digestion depends on stomach acid, produced by the parietal cells in the stomach when food enters the digestive tract. When the parietal cells don't secrete enough acid, or you take medications to reduce the acidity, the pH of the digestive juices in the stomach rises, or becomes less acidic. A less acidic environment interferes with the breakdown and digestion of food.
Chewing alone doesn't break up food enough for your body to digest it. The release of stomach acid in response to the presence of food initiates the churning and intestinal contractions that break food down into a semi-liquid soup called chyme. Food that passes through the intestines without breaking down can't nourish your body, because the nutrients inside never reach their target. The enzymes that further break down food work best in an acidic environment. Pepsin, an enzyme that breaks down proteins, works best in a pH environment between 1.8 to 3.5, the University of Washington website explains. Stomach acid also initiates the release of digestive enzymes from the pancreas, which also help break down protein and carbohydrates, pharmacist RoseMarie Pierce explains on her website, Holistic Pharmacist.
If stomach juices weren't extremely acidic, more bacteria and parasites found in food would make you sick. The low pH in the stomach creates an inhospitable environment for bacteria and parasites, killing them or severely decreasing their numbers before they can reach the intestines and make you seriously ill. Gastric acid with a pH of less than 3 can kill bacteria in less than 15 minutes, according to an Australian study published in the November 2007 issue of "Infection and Immunity." A pH over 4 reduces the anti-bacterial effect and can allow bacterial overgrowth.
Your body can't absorb certain vitamins, including vitamin B-12, without stomach acid. Hydrochloric acid, the main stomach acid, along with gastric protease, works to release B-12 from foods so your body can absorb it. When the parietal cells don't produce adequate amounts of the acid, you can't absorb B-12 well and you might develop anemia. Fat-soluble vitamins such as vitamins A and D, as well as the mineral calcium, also depend on a low gastric pH for optimal absorption. Gastric acid in the duodenum, the part of the small intestine nearest the stomach, also facilitates iron absorption, which also prevents anemia.
Risks of Reduced Stomach Acid
Producing less stomach acid -- a common occurrence as people age -- or artificially lowering it with medication to decrease acid reflux can have serious consequences. Poor nutrient absorption can lead to an increased risk of bone fractures as well as Clostridium difficile-associated diarrhea or community-acquired pneumonia, a University of Michigan review of studies published in the October 2009 issue of "Gastroenterology and Hepatology" found. Reduced stomach acid production could also interfere with the effectiveness of anti-platelet medications taken to reduce the risk of clot formation and cardiovascular disease.