WASHINGTON — An epidemic of obesity is compromising the lives of millions of American children, with burgeoning problems that reveal how much more vulnerable young bodies are to the toxic effects of fat.

In ways only beginning to be understood, being overweight at a young age appears to be far more destructive to well-being than adding excess pounds later in life. Virtually every major organ is at risk. The greater damage is probably irreversible.

Doctors are seeing confirmation of this daily: boys and girls in elementary school suffering from high blood pressure, high cholesterol and painful joint conditions; a soaring incidence of type 2 diabetes, once a rarity in pediatricians' offices; even a spike in child gallstones, also once a singularly adult affliction.

With one in three children in this country overweight or worse, the future health and productivity of an entire generation could be in jeopardy.

"There's a huge burden of disease that we can anticipate from the growing obesity in kids," said William H. Dietz, director of the Division of Nutrition, Physical Activity and Obesity at the federal Centers for Disease Control and Prevention. "This is a wave that is just moving through the population."

The trouble is a quarter-century of unprecedented growth in girth. Although the rest of the nation is much heavier, too, among those ages 6 to 19 the rate of obesity has not just doubled, as with their parents and grandparents, but has more than tripled.

Because studies indicate that many will never overcome their overweight — up to 80 percent of obese teens become obese adults — experts fear an exponential increase in heart disease, strokes, cancer and other health problems as the children move into their 20s and beyond.

The cumulative effect could be the country's first generation destined to have a shorter life span than its predecessor. A 2005 analysis by a team of scientists forecast a two- to five-year drop in life expectancy.

"Five years might be an underestimate," lead author S. Jay Olshansky of the University of Illinois at Chicago acknowledged recently.

COSTLY HEALTHCARE BILL

The epidemic is expected to add billions of dollars to the U.S. healthcare bill. Treating a child with obesity is three times more costly than treating the average child, according to a study by Thomson Reuters. The research company pegged the country's expense of care for overweight youth at $14 billion annually. A substantial portion is for hospital services, since those patients go more frequently to the emergency room and are two to three times more likely to be admitted.

Ultimately, the economic calculations will climb higher. No one has yet looked ahead 30 years to project this group's long-term disability and lost earnings, but based on research on the current workforce, which has shown tens of millions of workdays missed annually, indirect costs will also be enormous.

Childhood obesity is nothing less than "a national catastrophe," acting U.S. Surgeon General Steven Galson has declared. The individual toll is equally tragic. "Many of these kids may never escape the corrosive health, psychosocial and economic costs of their obesity," said Risa Lavizzo-Mourey, president of the Robert Wood Johnson Foundation, which has committed at least $500 million over five years to the problem.

The cycle of obesity and disease seems to begin before birth: Women who are overweight are more likely to give birth to bigger babies, who are more likely to become obese. "And so you build it up over generations," said Matthew Gillman, associate professor of ambulatory care and prevention at Harvard Medical School. "You get an intergenerational vicious cycle of obesity and disease."

MORE RISK FACTORS

As many as 90 percent of overweight children have at least one of a half-dozen avoidable risk factors for heart disease. Even with the most modest increase in future adolescent obesity, a recent study said the United States will face more than 100,000 additional cases of coronary heart disease by 2035.

The internal damage does not always take medical testing to diagnose. It is visible as a child laboriously climbs a flight of stairs or tries to sit at a classroom desk.

On a playground, obesity exerts a cruel price. "It robs them of their childhood, really," said Melinda S. Sothern of the Louisiana State University Health Sciences Center in New Orleans. "They're robbed of the natural enjoyment of being a kid — being able to play outside, run. If they have high blood pressure, they have a constant risk of stroke."

Physical therapist Brian H. Wrotniak, who works with overweight youth at Children's Hospital of Philadelphia, hears resignation more than anger in his patients' voices. "They complain of simple things like tying their shoes. They can't bend down and tie their shoes because excess fat gets in the way," he said.

Their usual solution: Velcro sneakers.

The emotional distress of these ailments, combined with the social stigma of being fat, makes overweight children prone to psychiatric and behavioral troubles.

"Obese children are victimized and bullied," said Jeffrey B. Schwimmer, a pediatric gastroenterologist at the University of California at San Diego and Rady Children's Hospital in San Diego. "Not only do other children treat them differently, but teachers treat them differently. And if you look at obese adolescents, their acceptance into college differs. For obese girls, their socioeconomic status is lower. It cuts a broad swath."