But now two American clinicians, James Braly and Ron Hoggan, have published a book, Dangerous Grains, claiming that what was thought to be a relatively rare condition may be more widespread than was previously thought. Braly and Hoggan suggest that gluten intolerance does not just affect a few people with CD, but as much as 2-3% of the population. They claim that gluten sensitivity (GS) is at the root of a proportion of cases of cancer, auto-immune disorders, neurological and psychiatric conditions and liver disease. The implication is that the heavily wheat-based western diet - bread, cereals, pastries, pasta - is actually making millions of people ill.

Your doctor, if asked about CD, would tell you that it involves damage to the gut wall, which makes for problems absorbing certain nutrients, such as iron, calcium and vitamin D. As a result, you are more likely to develop conditions such as osteoporosis and anaemia, as well as a range of gastrointestinal problems. Children who have it are often described as "failing to thrive". The proof that you have CD comes when gut damage shows up in a biopsy. The treatment, which has a high rate of success, is to remove gluten - found in rye and barley as well as wheat - from your diet.

But if Braly and Hoggan are right, the problem is far more widespread than the medical profession believes. Coeliac disease, they suggest, should be renamed "gluten sensitivity" and, in an appendix to the book, they claim that no fewer than 192 disorders, ranging from Addison's disease and asthma to sperm abnormalities, vasculitis, rheumatoid arthritis and hyperthyroidism, are "heavily overrepresented among those who are GS".

Dangerous Grains contains more than a dozen case histories of people who have recovered from a wide variety of chronic conditions - back pain, chronic fatigue, the auto-immune disorder lupus - simply by following a gluten-free diet. Both authors claim great personal benefits from such a change. "After eliminating gluten grains," writes Hoggan, "I realised how uncomfortable and chronically ill I had been for most of my life."

If you are someone who has visited a clinical nutritionist or a naturopath, this will come as no great surprise. One of their most common suggestions is temporarily to remove wheat from the diet to see if it makes a difference. In fact, so widespread has talk of a wheat allergy become that last November the Flour Advisory Board felt impelled to issue a statement warning of the dangers of this idea. Professor Tom Sanders, head of nutrition and dietetics at King's College, London, was quoted as saying: "Unless you suffer from coeliac disease, a very rare condition, cutting wheat out of your diet is extremely unwise."

Sanders certainly represents the mainstream medical view, but there is good evidence - such as the work of Dr Harold Hin, a GP from Banbury in Oxfordshire - to suggest that it may be in need of revision. Over the course of a year, Hin carried out a blood test on the first 1,000 patients who came to his surgery complaining of symptoms that might indicate CD, such as anaemia or being "tired all the time". Thirty proved positive and a diagnosis of CD was confirmed by a biopsy.

This indicated that CD was showing up at a rate of three per 100 - 30 times more than expected. Significantly, all but five had no gastrointestinal symptoms. "Underdiagnosis and misdiagnosis of coeliac disease," Hin concluded in an article for the British Medical Journal in 1999, "are common in general practice and often result in protracted and unnecessary morbidity."

More recently, a large research programme carried out by the University of Maryland Center for Celiac Research in Baltimore has confirmed Hin's findings. Scientists there tested 8,199 adults and children. Half the sample had various symptoms associated with CD and, of those, one in 40 of the children tested positive for CD and one in 30 of the adults.

But it wasn't just those who seemed ill who were having problems with wheat. Far more worrying was what the Maryland researchers found when they tested the other half of the sample, who were healthy volunteers, selected at random. Among kids under 16, one in 167 had CD, while the rate among the adults was even higher - one in 111.

If those proportions are true for the American population in general, this means that 1.8m adults and 300,000 children have undiagnosed CD - people who, sooner or later, are going to develop vague symptoms of feeling generally unwell, for which they will be offered various drugs that are unlikely to make much difference. Ultimately, they are at higher risk of a range of chronic diseases.

There seems, therefore, to be good evidence that CD is underdiagnosed. But Braly's and Hoggan's proposition is more radical than that. They believe that the immune reaction to gluten that damages the gut in CD can also cause problems almost anywhere else in the body. The evidence for this is a test involving a protein found in gluten called gliadin. When the body has an immune reaction, it makes antibodies. The test for anti-gliadin antibodies is known as AGA and people who test positive to AGA often have no sign of gut damage.

In fact, according to Dr Alessio Fasano, who carried out the University of Maryland research, "Worldwide, CD 'out of the intestine' is 15 times more frequent than CD 'in the intestine'." Braly estimates that between 10% and 15% of the US and Canadian populations have anti-gliadin antibodies, putting them at risk of conditions as varied as psoriasis, multiple sclerosis, jaundice, IBS and eczema.

The idea of gluten causing damage to parts of the body other than the gut is supported by another UK practitioner, Dr M Hadjivassiliou, a neurologist at the Royal Hallamshire Hospital in Sheffield. He ran an AGA test on patients who had "neurological dysfunction" with no obvious cause and found that more than half tested positive. What is more, only a third of the positive group had any evidence of CD gut damage. In other words, while the gluten antibodies can damage the bowels, they can also cause problems elsewhere. In this case, it was the cerebellum, or the peripheral nervous system.

So if a reaction to gluten can cause problems in the brain, might it also be linked to immune disorders? Braly and Hoggan certainly think so, and claim considerable clinical success in treating patients for conditions such as Addison's disease, lupus, rheumatoid arthritis and ulcerative colitis with a gluten-free diet. In fact, almost all the body's systems can be affected (see below). So if you suffer from a chronic condition that doesn't seem to respond to treatment, cutting out wheat for a while seems worth a try.

Are you gluten sensitive?

If you suffer from any of the following, the possibility that you are GS may be worth investigating.

· Upper respiratory tract problems such as sinusitis, "allergies", "glue ear"

· Symptoms related to malabsorption of nutrients such as anaemia and fatigue (lack of iron or folic acid), osteoporosis, insomnia (lack of calcium)

· Bowel complaints: diarrhoea, constipation, bloating and distention, spastic colon, Crohn's disease, diverticulitis

· Autoimmune problems: rheumatoid arthritis, bursitis, Crohn's disease

· Diseases of the nervous system: motor neurone disease, certain forms of epilepsy

· Mental problems: depression, behavioural difficulties, ADD

Contacts

University of Maryland Center for Celiac Research: 001-800-492 5538. Website: www.celiaccenter.org

For help on starting a gluten-free diet, visit www.inside-story.com

UK website for sufferers of coeliac disease: www.coeliac.co.uk

A good US website: www.celiac.com

York Nutritional Laboratory (01904 410410) conducts tests for various food sensitivities including gluten.