Babies with serious infections during their first year of life appear more likely to develop rheumatoid arthritis at an early age, Swedish researchers said on Tuesday.

Previous studies have suggested infections somehow trigger the autoimmune condition later in life but the Swedish findings raise the possibility infections may somehow change the way an immature immune system develops, the researchers said.

“Nobody had thought of this relationship with early-in-life infections and how they can affect the immune system,” said Cecilia Carlens of the Karolinska University Hospital and Institute in Stockholm, who led the study, published in the journal Annals of the Rheumatic Diseases.

Rheumatoid arthritis is an autoimmune disease and often strikes young people, resulting in pain, stiffness and swelling. It affects about 20 million people worldwide and is the most common chronic rheumatic disorder in children. Using data from national registers, the Swedish team tracked the health of more than 3,500 men and women born between 1973 and 2002.

The researchers looked at information on maternal health, pregnancy and birth details and whether the children had any infections during the first 12 months of life.

Compared to people without the conditions, children who had serious infections early on were more than twice as likely to develop rheumatoid arthritis as a young adult, the study found.

Babies born premature, small or with a low birth weight had a reduced risk for rheumatoid arthritis, but the researchers do not know why, Carlens added.

LONDON (Reuters)