Not surprisingly, sufferers will try anything to relieve the problem. One of the most popular remedies they turn to is diet. Unfortunately, the dietary experts, many of whom practise alternative medicine, cannot agree on which diet is the most effective, and many of the regimes they recommend are mutually exclusive. Some vilify acidic foods, others advocate them; some prohibit dairy products; others suggest wheat products are to blame.
One person who has decided to cut through this confusion is Dr Gail Darlington, consultant physician at Epsom Health Care NHS Trust, who has spent the past 14 years researching the relationship between diet and arthritis.
"I am working in this field as a completely orthodox rheumatologist," she says. "I am not a fringe practitioner. But I believe the medical profession's scepticism in this field is doing patients a disservice. By not taking their views into account, they are driving patients into the arms of quacks.
"If you tell patients that all diets are rubbish and all they need to do is take drugs, they may pay lip service to the idea, but they often go down the road to see an alternative practitioner, who may do them harm."
Dr Darlington's method is to try to discover if a patient is interested in diet, whether that patient's symptoms can be controlled by it and, if so, which foods they should avoid.
Her technique is simple. She puts patients on a restricted diet of fish, pears, carrots and mineral water for one week - foods that are unlikely to produce symptoms. "We then reintroduce one food at each meal, in a certain order, and if the new food does not cause symptoms, it is allowed, but if symptoms occur, it is omitted.
"It takes about six to eight weeks to test most foods, but often you know whether patients are food-sensitive in a week or two," says Dr Darlington, who has recently written a leaflet on diet and arthritis for the charity, Arthritis Care.
"Out of the first 150 patients we put through the programme, we found 38 could control their symptoms by diet alone. Others got some benefit but still had to take drugs, while many were not helped at all. So it does not help all patients.
"Some patients are very opposed to taking drugs, but if you give them the chance to discover whether a diet can work first, they are more willing to take some medication if the diet fails to help.
"A wide range of foods may give trouble. It is essential for dietary treatment to be medically supervised, to protect patients from excessively restrictive diets and also to ensure that, if diet is not relevant to a patient, they receive correct drug treatment, which may be essential."
One patient for whom this approach has been a godsend is Linda Oliver, a 45-year- old housewife from Kingston, Surrey, who has suffered from severe rheumatoid arthritis for five years, affecting her feet, hands, shoulders and jaw. She first guessed her illness might be affected by diet last summer, when she had a tummy bug. "I was not able to eat for days and I noticed that the pain in my joints reduced. I told the specialist at my local hospital and she referred me to Dr Darlington," she says.
"The elimination diet was gruelling, but it did highlight certain foods that were inclined to give me pain." The most important was wheat, and it meant she had to cut out bread, pasta, pizza, biscuits and cake. She also cannot eat runner beans, pineapple, melon, lettuce, leeks, eggs, cane sugar, oranges and some cheeses.
By cutting out these foods, her symptoms improved dramatically. "It was a revelation. I could suddenly walk around without this pain in my feet. It has made a big difference to me. I am much more comfortable. The swelling has gone down a bit in my hands. It is much easier to cope," she said.
The new diet also means she does not have to take such a high dose of drugs. She used to take 10mg of steroids a day; she now takes 2.5mg.
The only problem is that the diet is very restrictive. "It is difficult to stay on," she says. "I like good eating: pizza, wholemeal bread and so on. I get crabby if I can't eat what I want. I crave mature cheddar, buns and chocolate. Fortunately, my 13-year-old daughter is very supportive."
For breakfast, Mrs Oliver, who is a vegetarian, will often have a rice cake and banana; for lunch, such things as a salad of tomatoes, olives and feta cheese or a concoction of mushrooms, tomatoes and smoked salmon; and for supper, a stir-fried meal of vegetables and rice.
"You would think the fact that it reduces the pain would make it easy to stick to it. But sometimes I need nurturing and go in for comfort eating. I then suffer the next day. It's all a question of balance," she says.
Doctors in Norway have recently conducted a scientifically controlled study, using methods similar to those of Dr Darlington. Two groups of patients were compared over a year. One group ate a "normal diet" and another ate a gluten-free, vegan diet for the first five months. Other foods were gradually introduced on a trial basis: if they caused problems, they were dropped again. The results, which were published in The Lancet, showed that the second group had considerably reduced symptoms at the end of the study.
Nevertheless, many doctors remain unconvinced. Professor Rodney Grahame, consultant rheumatologist at Guy's Hospital, London, says: "It is difficult to judge the effect of diet in clinical trials on rheumatoid arthritis, because the disease sometimes goes into spontaneous remission and there are so many variables. Persuading any group to adhere strictly to a particular diet is also hard."
He believes that the regime which has the most convincing evidence is the fish oil diet. Clinical studies have shown that capsules containing fish oils, known as omega-3 marine triglycerides, can reduce inflammation of the joints.
Dr Darlington agrees that the evidence on fish oils is convincing, but believes more research needs to be done. "The problem is that fish oil in research studies has been used in very high doses. There is not much evidence to show that it works, if it is used in the way most patients use it, by taking one capsule a day. More studies need to be done," she says.
She is pleased there is a multi-centre study looking at evening primrose oil and would also like to see more work done on products such as vitamins, propolis, royal jelly and "devil's claw", because patients are turning to these supposed remedies yet no one really knows whether they work.
For Linda Oliver, cutting things out rather than putting things into her diet has done the trick. "I am lucky. I know someone else for whom the elimination diet did not work at all. But it made a big difference to me. It would be wonderful if other people were encouraged to have a go," she says.
Food for Thought, a Diet and Arthritis Special Edition, is available free from Arthritis Care Publications, PO Box 7516, London NW1 2JQ. Please send an A4 sae.Reuse content