Close contact with younger siblings during the first few years of childhood seems to reduce the risk of developing multiple sclerosis (MS) in adulthood, researchers from Australia report.

The link seems to be re-exposure to viral infections when young children are around.

“It has been proposed that early life infections may reduce the risk for allergic and autoimmune disorders, such as MS, by influencing the developing immune system,” Dr. Anne-Louise Ponsonby, who led the study, told AMN Health.

“Younger siblings may be important because they provide a source of common infant viral infections, and re-exposure to active viral infection is known to cause immune boosting and train immune responses,” she explained.

Ponsonby, from the Australian National University in Canberra, and colleagues gathered information on siblings from 136 adults with confirmed MS and 272 without MS.

Analysis of the information showed that adults with 1 to 3 years of contact with a younger sibling (less than 2 years old) during the first 6 years of life had a 43 percent reduced risk of developing MS. Longer contact further reduced the likelihood of developing MS, up to 88 percent, according to the team’s report in this week’s Journal of the American Medical Association.

The apparent protective effect of early-life infection on the development of MS is in line with increasing rates of MS, which has accompanied a decline in childhood infection rates over time, Ponsonby noted. “Further work is required to confirm these findings,” she emphasized.

SOURCE: Journal of the American Medical Association, January 26, 2005.