IELTS Academic Reading Practice Test 339

For most of the twentieth century, a peptic ulcer — an open sore in the lining of the stomach or of the first part of the small intestine — was treated as a chronic condition produced by the patient's way of life. The cause was assumed to lie in excess stomach acid, stress, a rich and spicy diet and smoking, and treatment followed accordingly. Patients took antacids to neutralise the acid, avoided certain foods and, in severe cases, underwent surgery to cut the nerves that stimulate acid production or to remove part of the stomach. The arrival in the late 1970s of drugs that blocked acid secretion, such as cimetidine, was hailed as a great advance, yet these medicines relieved the symptoms without removing the underlying problem, and ulcers commonly returned once treatment stopped.

A different explanation began to emerge in a hospital laboratory in Perth, Western Australia. Robin Warren, a pathologist at the Royal Perth Hospital, was examining tissue taken from patients' stomachs when he noticed something the textbooks did not mention: thin, curved bacteria lying in the layer of mucus that protects the stomach lining. They appeared in a high proportion of the samples he examined, and the tissue around them was inflamed. Warren began to record their presence systematically, and by 1979 he was convinced that the organisms were not merely present but associated with disease.

His colleagues were not persuaded, and their scepticism had a long history. The interior of the stomach was widely believed to be sterile, since few organisms could survive immersion in strong acid. Curved bacteria had in fact been observed in stomach tissue decades earlier, by researchers in Europe and elsewhere, but each report had been dismissed on the assumption that the samples had been contaminated during handling. Warren's findings therefore ran against an idea that had hardened into certainty, and the burden of proof lay with him.

Help arrived in the form of Barry Marshall, a young physician still in training, who heard about Warren's bacteria and asked to work with him. Their first task was to grow the organism in the laboratory, and for a long time they failed. Plates of nutrient gel were inoculated with tissue from patients and inspected after two days, the standard interval for the bacteria they were accustomed to handling, and nothing appeared. In 1982, over a long holiday weekend, a batch of plates was left in the incubator for five days instead of two. When the staff returned, colonies of the organism had grown.

Persuading the medical world proved far harder than growing the organism. The bacterium was first classified as a member of the genus Campylobacter and later given a genus of its own, becoming Helicobacter pylori. A short letter describing the link between the organism and inflammation of the stomach lining appeared in The Lancet in 1983, and a fuller paper followed in 1984, after other journals had turned the work away. At conferences the two Australians attracted small audiences and sharp criticism, and many gastroenterologists continued to regard the bacteria as harmless passengers.

Marshall then took a step that has become part of medical folklore. Because the organism appeared to infect only humans and a few other primates, the usual animal experiments were unavailable, so in 1984 he drank a suspension of the bacteria himself. Within about a week he was suffering from nausea and stomach pain, and biopsies showed that his stomach lining had become inflamed, with the bacteria visible in the tissue. A course of antibiotics restored him. The experiment did not by itself prove that the organism causes ulcers, but it established that it could colonise a healthy stomach and produce gastritis.

Treatment followed slowly. Combinations of antibiotics with bismuth, a compound long used for stomach complaints, were shown in trials during the late 1980s to eliminate the bacterium and to prevent ulcers from recurring. Even so, many specialists remained reluctant to abandon the idea that ulcers were a consequence of stress and excess acid, and the drugs that suppressed acid were highly profitable. The turning point came in 1994, when a consensus conference convened by the United States National Institutes of Health concluded that infection with the bacterium was the principal cause of peptic ulcers and that patients should be given antibiotics. Practice then changed, though not everywhere at once.

The scale of the infection is remarkable. Helicobacter pylori is thought to be present in roughly half the world's population, yet the great majority of carriers never develop symptoms, and only a small minority go on to suffer ulcers. Why the bacterium is destructive in some people and harmless in others remains one of the unresolved questions of the field. In 1994 the International Agency for Research on Cancer, a body linked to the World Health Organization, classified the organism as a carcinogen, a definite cause of cancer in humans, on the basis of its association with cancer of the stomach.

In 2005 Warren and Marshall shared the Nobel Prize for physiology or medicine for their discovery. The award recognised not only a specific medical advance but a change in attitude: a reminder that the weight of expert opinion is not evidence, and that an observation made through an ordinary microscope in a routine hospital laboratory can overturn a theory that has stood for a century.

A strong solution of hydrochloric acid will corrode metal, dissolve limestone and destroy living tissue. The human stomach secretes precisely that chemical, concentrated enough to reach a pH of 1.5, and holds it there for an hour or more after every meal. The acid begins the breakdown of food, activates digestive enzymes and destroys most of the microbes that arrive with it. Yet the same fluid does not normally digest the stomach itself, even though the stomach wall is made of the same protein and fat as the food it processes. Explaining why it does not requires attention to a set of defences that operate at scales from the whole organ down to individual molecules.

The acid is produced by parietal cells, large cells set deep in the pits and glands of the stomach wall. When a meal arrives, signals from the vagus nerve and from the hormone gastrin prompt these cells to pump hydrogen ions into the stomach cavity; chloride ions follow, and the result is hydrochloric acid. The concentration of hydrogen ions inside the stomach can be a million times that within the cells that secrete them, so the process consumes a good deal of energy. The pH of an empty stomach is usually between 1.5 and 3.5, rising towards neutral once food has buffered the acid. The acid does three jobs: it unfolds proteins so that enzymes can attack them, it converts the inactive precursor pepsinogen, released by neighbouring chief cells, into the protein-splitting enzyme pepsin, and it disables most ingested bacteria.

The first line of defence is the mucus that coats the lining. Surface cells secrete a gel of large sugar-bearing proteins, or mucins, which adheres to the epithelium and forms a layer well under a millimetre thick. Into this gel the same cells release bicarbonate ions. The result is a steep gradient: the stomach cavity is fiercely acidic, while the fluid immediately next to the cell membrane is close to neutral. The gel also slows the diffusion of acid, so that the bicarbonate has time to keep pace with it. Pepsin, which requires acid in order to work, is largely inactive in this alkaline zone, and the acid itself is neutralised before it can reach the cells.

Beneath the gel, the surface cells are sealed to one another by tight junctions, bands of protein that prevent acid from seeping between them, and the membranes facing the cavity are unusually resistant to acid. Even so, some damage is inevitable, and the lining is rebuilt continuously. Stem cells deep in the glands divide and migrate upwards, replacing the surface layer every few days. Because cells injured by acid, alcohol or infection are shed and replaced so quickly, damage that would be permanent elsewhere in the body heals within a week.

The defences are actively managed by prostaglandins, short-lived chemical messengers made in the stomach wall. These compounds stimulate the surface cells to secrete more mucus and more bicarbonate. They also widen the blood vessels that supply the lining, so that the flow of blood through it increases. That flow performs two services: it carries away any acid that has managed to penetrate the barrier, and it delivers the bicarbonate on which the surface cells depend. The lining is therefore not a passive wall but a system that reacts to insult.

Two common disturbances show what happens when this system is weakened. Non-steroidal anti-inflammatory drugs, the aspirin-like painkillers taken by millions of people, block the enzyme that makes prostaglandins. With prostaglandin production suppressed, less mucus and bicarbonate are secreted and blood flow falls, which is why long-term use of these drugs can cause ulcers; the risk rises with dose and with age. The bacterium Helicobacter pylori takes a different route. It lives within the mucus layer and produces an enzyme that generates ammonia, neutralising the acid immediately around it, while the immune response it provokes does further damage to the lining. Alcohol and severe physical stress add to the burden, though the mechanisms are less well understood.

The system is easy to describe in outline and difficult to measure in detail. The mucus gel is only a fraction of a millimetre thick and deforms at the slightest touch, so a probe inserted through an endoscope disturbs the very structure it is trying to record. Much of what is known comes from laboratory animals and from tissue studied after removal, where behaviour may differ from that in a living person. Direct measurements in healthy volunteers have been attempted, but they require techniques that few laboratories possess, and results from different centres have proved hard to compare. Estimates of the layer's thickness vary widely between studies, and whether it forms a continuous sheet or a patchwork of thicker and thinner regions has been argued over for decades.

The mucus layer is far from lifeless: a varied community of bacteria lives in it, and recent work suggests that this community interacts with the immune system in ways that are only beginning to be understood. Some researchers argue that differences in the resident bacteria help explain why H. pylori causes ulcers in a minority of those who carry it while leaving the majority unaffected. If they are right, the state of a person's mucus layer may matter as much as the bacterium itself. Such claims remain speculative, but they indicate that the stomach is better understood as an ecosystem than as a simple vessel of acid.

Ask people how much salt they eat and most will think of the salt cellar. In fact, in countries such as Britain, Australia and the United States, roughly three-quarters of the salt in the average diet is already in the food before it reaches the kitchen: in bread, cheese, cured meat, sauces, breakfast cereals and ready meals. Bread, which few people would describe as salty, accounts for a substantial share of the total. National surveys generally put average consumption somewhere between eight and twelve grams a day, well above the maximum of five grams, about a teaspoon, that the World Health Organization recommends for adults. Cutting back at the table therefore achieves little. The decision about how much salt most people consume is taken by food manufacturers, not by individuals.

Salt matters because of what it does to blood pressure. Sodium, the component of salt that the body absorbs, draws water into the bloodstream, increasing the volume the heart must pump and the pressure inside the arteries. Over years, raised blood pressure thickens and stiffens the artery walls and damages organs: it is the leading risk factor for stroke and a major cause of heart attacks and kidney disease. Because these conditions are common and disabling, even a small shift in the distribution of blood pressure across a whole population translates into a large number of avoided events.

The evidence that reducing salt lowers blood pressure rests on a large body of randomised trials, summarised in systematic reviews that pool well over a hundred studies. In people with normal blood pressure the fall is modest, of the order of a couple of millimetres of mercury; in those with hypertension it is larger. The size of the response varies considerably between individuals, and the reasons for that variation are not fully understood, though age, kidney function and genetic factors all appear to play a part. Even a modest average fall, multiplied across a population, is thought to prevent a significant number of strokes.

Not all researchers accept that lower is always better. A large international study published in 2018 followed tens of thousands of adults in eighteen countries and reported that cardiovascular risk rose with high sodium intake but also, unexpectedly, at the lowest intakes. The finding, widely publicised, has been vigorously contested. Critics have pointed out that a single urine sample collected in the morning is a poor guide to a person's habitual intake, that the method used to estimate sodium from it may be unreliable, and that people who are already ill often eat less. The debate is unresolved, and it would be dishonest to pretend otherwise.

The question for policy is therefore not whether salt matters but what a government can usefully do about it. The most promising approach is reformulation: persuading manufacturers to reduce the salt in their products gradually, a little at a time. Britain ran such a programme from 2003, with targets for each category of food drawn up by the Food Standards Agency after discussion with industry. Because the reductions were small and spread over years, consumers did not notice; taste receptors adapt to lower levels of salt within weeks. National diet surveys recorded a fall in average intake, and the approach has been copied, with varying success, in other countries.

Other measures have a weaker record. Front-of-pack labels, which display salt content in a standard format, help shoppers who read them, but the effect on the whole population is modest and concentrated among those already motivated to change. Public campaigns shift awareness more readily than behaviour. Taxes on salty foods are theoretically attractive and have been used for sugary drinks in several countries, but they fall on a wide range of basic foods and would hit poorer households hardest.

Opponents make two arguments. The first is about freedom: people should be allowed to eat what they like, and a government that sets limits on salt is on a path towards regulating every pleasure. This argument has real force in matters of genuine choice, but it is weaker here, since the choice has already been made by someone else before the food reaches the shelf. The second concerns cost, particularly for small producers who cannot afford to reformulate their products or employ food technologists. Both objections deserve an answer; neither seems decisive.

There is also an unintended consequence to consider. In many countries salt is the main vehicle for iodine supplementation, a public-health measure that has greatly reduced thyroid disease and impaired development in children. Reducing salt without adjusting iodine levels risks undoing part of that gain. The solution is straightforward: keep the iodine concentration in salt under review as salt consumption falls, and use other vehicles if necessary. The risk is real but manageable, and it is an argument for careful policy design rather than for inaction.

My own view is that governments should act, but with modest and evidence-led instruments. Mandatory reformulation targets, reviewed every few years and tightened when the industry falls short, seem preferable to taxes or bans. Voluntary agreements can work, as the British experience suggests, but only when a credible threat of regulation stands behind them. Salt reduction is not a dramatic intervention, and it will not transform health on its own. It is, however, one of the cheaper and better-evidenced measures available, and the evidence for it has been accumulating for four decades.