The Harvard School of Public Health alleges the tobacco industry manipulated the menthol content of cigarettes to hook young smokers.

Researchers said a study of internal industry documents and independent lab tests showed cigarette makers adjusted levels of menthol "to create a milder experience for the first-time smoker."

The study is published online in advance of the American Journal of Public Health's September 2008 issue.

"For decades, the tobacco industry has carefully manipulated menthol content not only to lure youth but also to lock in lifelong adult customers," co-author Howard Koh said Wednesday in a news release. The report said tobacco companies determined that milder brands with lower menthol levels appealed to younger smokers.

The study comes as Congress considers a bill that would allow the U.S. Food and Drug Administration to regulate additives such as menthol.