By Maxine Frith
Bigger babies and children who are breast-fed have a higher risk of developing rheumatoid arthritis in later life, researchers say.
The findings are surprising because diseases are normally linked to lower birth weight, and breastfeeding has been shown to protect against many health problems in later life. Experts believe the study adds to increasing evidence that rheumatoid arthritis may be triggered by infection.
Nearly 400 000 people in the UK, most of them women, suffer from the disease. It inflames joints, causing serious damage and agonising disability in severe cases.
The study was carried out by researchers from Malmo University in Sweden, who examined the records of 77 people with rheumatoid arthritis born between 1940 and 1960. They compared their details to 308 people of the same age who did not have the condition.
People who weighed more than 4kg) at birth were three times more likely to have rheumatoid arthritis than those of average birth weight - 3,4kg. Breast-fed babies and the children of manual workers were also more likely to suffer from the condition.
Dr Madeleine Devey, scientific adviser at the Arthritis Research Campaign, said: " is extremely interesting. It is quite unusual to find an association between high birth weight and disease."
She added: "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."
Rheumatoid arthritis is an autoimmune disease in which the body's own cells begin attacking the joints. There is no cure and the symptoms can only be alleviated with painkillers, though new drugs are being developed. More than 12 000 new cases are diagnosed every year in the UK and the incidence appears to be rising.
Scientists believe it may be caused by a microbial infection that triggers an allergic reaction, turning the immune system on itself.