Eating a large amount of red meat has been linked to an increased risk of developing rheumatoid arthritis, scientists say.
High red meat consumption has also been linked to cancer
A study showed people who ate meat every day had double the risk of the disease compared to those who ate meat less, perhaps twice a week.
Researchers studied the dietary habits of 25,000 people.
The University of Manchester study is published in the journal Arthritis and Rheumatism.
Rheumatoid arthritis (RA) causes inflammation of the membrane lining the joint, causing them to feel tender, stiff and swollen. Around 387,000 in the UK have the condition.
Immune system trigger
Study participants were aged between 45 and 75 were recruited via GP lists between 1993 and 1997. All were asked to complete a seven-day food diary detailing exactly what they ate, and how large the portions were.
Researchers then looked at the incidence of RAs among the group until 2002.
They found 88 people had been diagnosed with RA, or a related form of arthritis, and compared their diets with 176 healthy participants to see how their eating habits differed.
The researchers suggest something in meat, perhaps collagen, could trigger an immune system response, which may also affect joints.
Iron is another possible candidate. It has been shown to accumulate in the rheumatoid synovial membrane, causing tissue damage.
Other studies have shown Mediterranean countries, where red meat tends to feature less in diets, have lower levels of RA.
Vegetarian and vegan diets have also been linked to reduced risk.
Professor Alan Silman, Director of the Arthritis Research Campaign epidemiology unit at the University of Manchester, said: "Meat consumption may be linked to either additives or even infectious agents, but there is no evidence as to what
might be important in relation to rheumatoid arthritis."
He added: "This is the first time this link has been made."
The people who developed RA were more likely to be former smokers and to eat less food containing vitamin C, but the researchers said the most significant difference between them was their meat-eating habits.
The team also found that eating more protein overall, including other forms of meat and plant protein, also increased the risk of developing RA, while eating fat did not seem to raise the risk.
Other risk factors
A spokeswoman for the Arthritis Research Campaign, which funds the epidemiology unit, said: "This study provides further evidence that environmental factors can help to trigger rheumatoid arthritis.
"In the light of this new evidence we would suggest that as part of a healthy lifestyle, people should cut down the amount of red meat (beef and lamb) they eat."
She added: "We wouldn't want people to think that if they eat four burgers a week they are going to develop rheumatoid arthritis the following week because there are other risk factors that come into play - genetic susceptibility, smoking, low intake of Vitamin C.
"Red meat in itself is not dangerous to health, but should be eaten in moderation as part of a balanced, healthy diet."
Mo Atchia, a spokesman for Arthritis Care, added: "Diet has become an increasingly important factor in living with arthritis, and studies such as this one can only help our understanding of the way a person's diet can impact on their condition.
"A low-fat, high-fibre diet, with plenty of fruit and vegetables for people with arthritis is vital to maintaining good general health."