The findings help explain disproportionately high obesity rates in minority children. Family income is often a factor, but so are cultural customs and beliefs, the study authors said.
They examined more than a dozen circumstances that can increase chances of obesity, and almost every one was more common in black and Hispanic children than in whites. Factors included eating and sleeping habits in infancy and early childhood and mothers smoking during pregnancy.
In a separate, equally troubling study, researchers found signs of inflammation in obese children as young as 3 years old. High levels were more common in blacks and Hispanics.
These inflammatory markers have been linked with obesity in adults and are thought to increase chances for developing heart disease. Their significance in early childhood is uncertain, but the study's lead author says she never thought they'd be found in children so young.
"We think that fat cells in the body cause inflammation and that inflammation causes vessel damage," said University of North Carolina researcher Asheley Cockrell Skinner, the lead author.
The results suggest that 3-year-olds with inflammation might already have artery changes that could make then prone to later heart problems, although that needs to be examined in future research, she said.
Both studies were released Monday in the journal Pediatrics.
Dr. Reginald Washington, a Denver pediatric heart specialist who has worked with the American Academy of Pediatrics on obesity issues, called both studies important.
He said they underscore the merit of first lady Michelle Obama's campaign against childhood obesity.
"You still have to get the public to say we believe this is a problem," Washington said. "Everybody's going to have to play a role here."
Twenty percent of black and Hispanic children ages 2 to 19 are obese, versus 15 percent of whites, recent government data show.
In the racial disparities study, risk factors examined included: mothers smoking during pregnancy; unusually rapid weight gain in young infants; starting solid food before 4 months; mothers' routinely pressuring young kids to eat more; children sleeping less than 12 hours daily between 6 months and 2 years; and allowing very young kids to have sugary drinks, fast-food, and/or TVs in their rooms.
Minorities were at higher risk than whites for nearly every one.
"It's striking," said lead author Dr. Elsie Taveras of Harvard Medical School.
The researchers questioned 1,826 Boston-area mothers, but Taveras said the study results apply to youngsters nationwide.
Many circumstances studied are more common in low-income, less educated families, including whites. Taveras said the researchers accounted for that and still found race was frequently a factor regardless of income.
The results may reflect cultural beliefs or influence from grandparents on feeding practices, but the good news, she said, is that almost every risk factor studied can be changed.
The separate, inflammation study involved data on more than 16,000 children aged 1 to 17 who had blood tests during 1999-2006 national health surveys.
Inflammation markers including a substance called C-reactive protein or CRP were measured. CRP levels of at least 1 milligram per deciliter of blood have been linked with heart disease risks in adults.
Starting at age 3, very obese children were more likely than less heavy kids to have levels at least that high. Even higher levels were most common in black and Hispanic kids.
Skinner said it's unlikely that elevated levels will cause problems at age 3. But researchers don't know if the presence of these markers at such a young age might put children at risk for heart problems early in adulthood.
Infections also can cause elevated CRP levels; the researchers took that into account and also excluded children with chronic illness.
The results are preliminary and do not mean that parents of obese kids should rush out and have their kids' CRP levels tested, Washington said. That's partly because it's not clear if lowering CRP levels in obese kids, through weight loss for example, would make any difference, he said.