People who had more exposure to infant siblings during the first six years of life have a lower risk of developing multiple sclerosis than people with less exposure, potentially because of increased childhood infection and related immune responses, says a study published this week.

The study looked at 136 adults (average age 43.5 years) with multiple sclerosis confirmed by magnetic resonance imaging and 272 controls (average age 43.6 years) matched by sex and year of birth. The participants, all residents of Tasmania, were interviewed between March 1999 and June 2001.

The aim was to assess whether a range of factors, including exposure to infant siblings in early life, was associated with the risk of developing …