Summary - H2 blockers are drugs used to reduce stomach acid in people who have pain due to stomach ulcers. Vitamin U in the form of fresh vegetable juice or supplements can be used alongside H2 blockers to speed up the restoration of the protective mucous bilayer.
The human stomach is a very acidic environment. The pH of a correctly-functioning stomach is 1.5 - 3. The acidity of gastric juice is due to hydrochloric acid (HCl), which is produced by parietal cells in the upper parts of the stomach (fundus and cardia). Parietal cells produce acid using enzymes called proton pumps (H+/K+ ATPase), which use the energy derived from the hydrolysis of ATP to pump H+ into the stomach. It is the protons (H+) that cause acidity.
The parietal cells pump acid into the stomach in response to signal molecules binding receptors. There are numerous kinds of receptors that respond to different stimuli, either positively or negatively. The most important for acid production are the H2 histamine receptors. Protein in food is broken down in the stomach by acid and the enzyme pepsin to form peptides. These peptides stimulate the release of the hormone gastrin from G cells in the stomach and duodenum. Gastrin stimulates the release of histamine from ECL cells. Histamine binds receptors in the base of parietal cells where it stimulates the movement of proton pumps to the apical surface, where they pump acid into the stomach cavity (lumen). This acid accelerates this whole cycle, breaking down more proteins in food by hydrolysis as well as activating pepsin.
H2 blockers bind to the H2 receptors, which stops histamine from binding. If histamine can't bind, the levels of acid in the stomach remain fairly low and the corresponding pH relatively high. (H2 blockers are often referred to as H2 antagonists because they block the binding of histamine without itself stimulating the function of the receptor, an important distinction from agonists).
H2 blockers were invented in the 1960s and have to a large extent been superseded by proton pump inhibitors due to the latter's more potent acid-suppressing abilities. Commonly used H2 blockers include omeprazole (e.g. Prilosec), famotidine (e.g. Pepcid) and cimetidine (e.g. Tagamet). Ranitidine (e.g. Zantac) was the most prescribed drug in the US during the 1980s, but the FDA has recently banned its sale due to carcinogenic impurities.
Stomach ulcers and gastroesophageal reflux (GERD) are conditions characterized by pain caused by stomach acid coming into direct contact with the lining of the stomach and esophagus, respectively. Contrary to popular opinion, these conditions are rarely caused by excessive production of stomach acid. In fact, the acidity in the stomach of those with stomach ulcers is typically low (i.e. relatively high pH). GERD is caused by normal stomach acid coming into contact with the esophagus, an organ that is not designed to withstand such exposure. Unlike the stomach, the esophagus is not coated with a protective alkaline mucous bilayer and is very sensitive to contact from even small amounts of gastric juice.
One unfortunate problem with taking H2 blockers for stomach ulcers is that they reduce the secretion of mucin (Ichikawa et al., Diebel et al). So while they reduce pain by reducing the amount of acid produced, they also increase the risk of pain by weakening the mucous bilayer.
Vitamin U is a nutrient abundant in vegetables and fruit that stimulates the secretion of mucin in the stomach. As fresh vegetables and fruit have been a major component of our diet for a very long time, it is reasonable to conclude that dietary Vitamin U plays an important role in the maintenance of optimal stomach function.
Can Vitamin U be combined with H2 blockers?
Considering Vitamin U stimulates mucin secretion and H2 blocker reduce it, one may wonder whether Vitamin U can be taken with H2 blockers to negate the negative effects. The evidence suggests yes. In 2009, Ichikawa et al. showed that co-administration of Vitamin U with famotidine reversed the mucin-blocking effects of famotidine without affecting the acid-suppression effects. These results suggest that Vitamin U can add another level of protection to the gut in those taking H2 blockers.