Big babies may be more likely to develop rheumatoid arthritis later in life, according to a study.
An estimated 400,000 Britons have the condition
Researchers in Sweden have found evidence to suggest that people who are relatively heavy at birth have a greater chance of developing the condition when they grow old.
Rheumatoid arthritis or inflammation of the joints affects almost 400,000 people living in the UK, most of them women.
In severe cases, it can cause serious joint damage or even disability.
'No clear cause'
There is no clear cause. Rheumatoid arthritis occurs when the body's immune system turns on itself and attacks tissue.
Genetic factors are known to play a role but not in every case. Some scientists believe it can be triggered by an infection.
Other research has suggested that birth factors, such as birth size or breast feeding, could also play a role.
Dr Lennart Jacobsson and colleagues at Malmö University Hospital studied the records of 77 people with rheumatoid arthritis who were born between 1940 and 1960 to see if this was the case.
Their records were compared to 308 people of the same age who did not have the condition.
The researchers found that people who weighed more than 4kg or 8.8lbs at birth were three times more likely to have rheumatoid arthritis compared to those who were lighter. Average birth weight is 3.4kg or 7.5lbs.
They also found that people who were breast-fed soon after they were born and whose father was a manual workers were also more likely to develop the condition.
The researchers said the findings suggested that the time in and around birth was important in determining whether someone went on to develop rheumatoid arthritis.
They suggested high birth weight and early breast feeding may affect the immune system, which then turns on the body later in life to trigger the condition.
The UK's Arthritis Research Campaign welcomed the study.
Dr Madeleine Devey, its scientific advisor, said: "It is extremely interesting. It is quite unusual to find an association between high birth weight and disease.
"One explanation may be that people with fairly affluent parents may suffer fewer infections, which is a potential risk factor for rheumatoid arthritis. Obesity in adults is also associated with the disease."