The earlier in life children reach their lowest body mass index (BMI) signals potential heart disease risk factors and may become evident as early as age 7, researchers reported at the American Heart Association's Scientific Sessions 2007.
Researchers studied "BMI rebound age" -- the age at which BMI reaches its lowest point before increasing through later childhood, adolescence and adulthood.
The new study, one of the first of its kind, investigated BMI rebound age in 308 children, 158 boys and 150 girls, beginning at age 3 and looked at adverse cardiovascular risk effects at age 7.
"Obesity is a problem that develops early in childhood and has adverse cardiovascular consequences early in childhood," said Thomas R. Kimball, M.D., senior author of the study and professor of pediatrics at the University of Cincinnati College of Medicine in Ohio.
Healthy children entered the study at age 3 and were measured for BMI every four months for the next four years until they reached age 7. The majority of the children, primarily Caucasian, were drawn from the pediatric primary care center at Cincinnati Children's Hospital.
The BMI low point is between ages 4 and 7 years. The laboratory studies done at age 7 determined the risk factors for heart disease. Echocardiograms evaluated left ventricular mass and left atrial size.
The study found earlier BMI rebound age was associated with adverse risk factors for heart disease as measured at age 7: higher BMI, higher systolic and diastolic blood pressures, higher serum insulin and leptin levels, higher left ventricular mass and left atrial size.
The children were divided into three groups based on age of BMI rebound:
- Early BMI rebound age (below the 25th percentile)
- Middle BMI rebound age (between the 25th and 75th percentiles)
- Late BMI rebound age (above the 75th percentile)
BMI rebound age for children in the 25th percentile was 4.4 years for boys and 4.2 years for girls. In the 75th percentile, the BMI rebound age was 6.6 years for boys and 5.7 years for girls.
"The study implies that girls may have earlier BMI rebound age than boys," Kimball said. "Earlier rebound age correlates with greater likelihood to become obese adults, so girls may be more at risk to become obese adults." Jennifer Jaworski, lead author of the study and a third-year medical student at the University of Cincinnati College of Medicine in Ohio, said she and her colleagues found statistically significant differences between children in the 25th percentile BMI rebound age and those in the 75th percentile of BMI rebound age.
Prevalence of overweight children in the United States is increasing, according to the National Health and Nutrition Examination Survey (NHANES): in 2003--04, an estimated 17 percent of children 2 to 19 years old and 18.8 percent of children ages 6 to 11 were overweight (an increase from 16.3 percent in 2001--02).
Kimball said it's important for physicians to measure BMI and BMI rebound age in younger children as well as adolescents.
Kimball also said that "these problems of overweight and cardiac risk factors begin at an early age, not just in teenage or adult years. As a physician and parent, I'd rather deal with these issues before the habits are set. The crux of the matter is when these habits are set in childhood, they are difficult to break. It's not just the child's problem, but becomes a family issue."
Co-authors are Philip Khoury, M.S.; Robert Cohen, Ph.D.; and S. R. Daniels, M.D., Ph.D.
The National Institutes of Health funded the study.
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