Oct. 14 (HealthDay News) -- More than half of sudden infant deaths involve babies who share a bed or sofa with a parent, and alcohol or drug use by parents appears to be a factor in many of the cases, says a U.K. study.

Researchers analyzed 80 cases of sudden infant death syndrome (SIDS) in southwest England between January 2003 and December 2006. Of the deaths, 54 percent occurred while parent and child were sharing a bed or sofa, called co-sleeping. Parental use of alcohol or drugs before co-sleeping occurred in 31 percent of the cases, and 17 percent of the deaths occurred while co-sleeping on a sofa.

One-fifth of the infants were found with a pillow and one-quarter were swaddled, the study authors noted, suggesting these situations as potential risk factors.

The study included a number of different social groups, and the results suggest that the risk factors were similar throughout the entire community, which the study said indicates that the deaths were not related to social deprivation.

The findings appear online Oct. 14 in BMJ.

The safest place for an infant to sleep is in a separate bed beside the parents' bed for the first six months of life, according to the researchers, from the University of Bristol and University of Warwick. They urged parents to never put themselves in a situation where they might fall asleep with a young infant on a sofa and to never co-sleep with an infant in any environment if they've been taking drugs or drinking alcohol.

SIDS is largely preventable, but parents have to be educated about proper infant care practices, Edwin Mitchell, professor of child health research at the University of Auckland, wrote in an accompanying editorial.

SOURCE: BMJ, news release, Oct. 14, 2009