A rare study that tracked thousands of children through adulthood found the heaviest youngsters were more than twice as likely as the thinnest to die prematurely, before age 55, of illness or a self-inflicted injury.

Youngsters with a condition called pre-diabetes were at almost double the risk of dying before 55, and those with high blood pressure were at some increased risk. But obesity was the factor most closely associated with an early death, researchers said.

The study, published Thursday in The New England Journal of Medicine, analyzed data gathered from Pima and Tohono O’odham Indians, whose rates of obesity and Type 2 diabetes soared decades before weight problems became widespread among other Americans. It is one of the largest studies to have tracked children for several decades after detailed information on weight and risk factors like high cholesterol were gathered.

“This suggests,” said Helen C. Looker, senior author of the paper and assistant professor of medicine at Mount Sinai Medical Center in New York City, “that obesity in children, even prepubescent children, may have very serious long-term health effects through midlife  that there is something serious being set in motion by obesity at early ages.” Dr. Looker added, “We all expect to get beyond 55 these days.”