When you’re feeling too ill to eat, or have indigestion, what could be better than a gentle, thick glass of milk to settle your stomach? It’s soothing to drink, and at least you are getting something nutritious inside you. This remedy has been around for years in countries where milk is popular. Until the 1980s, doctors would sometimes recommend milk to patients with duodenal ulcers (in the intestine just beyond the stomach) to help ease their discomfort.
Milk is in fact slightly acidic, but far less so than the gastric acid naturally produced by the stomach. So it was long thought that milk could neutralise this stronger acid and relieve the pain. Milk does help provide a temporary buffer to gastric acid, but studies have shown that milk stimulates acid production, which can make you feel sick again after a short period of relief.
In 1976, ten hardy research participants put themselves forward to test this out. They had their stomachs emptied and were then fed milk through a tube up their nose. An hour later the contents of their stomachs were sucked out again and then gastric acid secretion was measured every five minutes. The researchers found that milk caused an increase in the secretion of gastric acid for the next three hours, which could explain why people with ulcers typically experience pain a few hours after a meal.
It’s not just milk, though. Studies comparing coffee, tea, beer and milk found they all stimulated the secretion of acid. Beer and milk have the greatest effect, which suggests, somewhat surprisingly, that the pH of a drink is irrelevant when it comes to acid production.
So what is the ingredient in milk that causes the stomach to produce acid? Researchers in the 1976 study looked at fat by comparing whole, low-fat and fat-free milk. All increased acid secretion. How about calcium? When they tried the experiment using low-calcium milk, less acid was produced, but there was an exception. The patients who had evidence of duodenal ulcers, but were not currently experiencing symptoms, produced more acid.
The other ingredient which might stop milk from settling your stomach is the milk protein casein. It is thought it either stimulates the release of the hormone gastrin, which in turn controls the production of gastric acid, or it stimulates directly the cells in the stomach lining, known as parietal cells, to release acid.
Either way, milk is no longer recommended for people with ulcers because it might do the opposite of soothing them. It could make them worse. In 1986 patients with duodenal ulcers spent four weeks in hospital on medication as part of a controlled trial. One unlucky group was assigned to drink only milk – two litres a day in total, with added sugar if they preferred. The other group ate the usual hospital diet and both groups were also offered additional fruit, so there was a similar total intake of calories between the two groups. At the end of the four weeks each patient underwent an endoscopy to examine their ulcers. Significantly more people on the standard diet had ulcers that had healed, while fewer than expected got better in the milk-drinking group. Milk appeared to hinder the healing process.
If you are well, drinking milk is still encouraged, as it is a good source of protein and calcium. But could very large quantities of milk present a problem? In 1980, 21,000 adults in the city of Tromso in Norway were invited to join a health study where they would be followed for seven years, during which time 328 developed peptic ulcers (an umbrella term covering duodenal and stomach ulcers). They found that heavy milk drinkers (defined as four or more glasses a day) were more likely to develop an ulcer, especially amongst the men. Again, it made no difference whether the milk was full fat or skimmed. So was the milk causing the ulcers? The difficulty here is that some people with pain drink milk to ease the symptoms temporarily, so perhaps they were consuming milk as a result of the ulcer. But the risk was also high in those drinking large quantities of milk, despite not having symptoms, so it’s hard to disentangle the causality.