October 8, 2010
Dear Mayo Clinic:
Is body mass index in children a predictor of their future health?
Body mass index (BMI) is defined as a person's weight in kilograms divided by the square of their height in meters. BMI can help determine if a child is at a healthy weight. Children with a BMI measure that's too high may be at increased risk for health problems, such as cardiovascular disorders and diabetes.
In children, BMI is taken in conjunction with age and gender and plotted on a growth chart with percentiles to assess a child's level of body fat. Generally, children with BMI between the 5th and 85th percentiles are considered to be at a healthy weight. Those less than the 5th percentile are underweight. Children between the 85th and 95th percentiles are overweight, and those at or above the 95th percentile are obese.
Because BMI doesn't measure body fat directly, a person who has a high level of body muscle and a low level of fat can have a high BMI level, as may be the case with athletes. But, for practical purposes, BMI is typically a reliable, inexpensive way to evaluate a child's weight.
A child with a high BMI is at an increased risk of health problems. Research has shown that high BMI predisposes children to developing high blood pressure, high cholesterol and type 2 diabetes. These problems can occur during childhood, or they may develop as a child grows into adulthood.
In addition to the specific health conditions that may develop as a result of being overweight in childhood, one-half to three-fourths of overweight children become overweight adults. So a child with a high BMI has a high likelihood of becoming an overweight adult unless preventive steps are taken early. That's why regularly monitoring a child's weight is important. If a child's BMI begins to climb, the trend is much easier to reverse in the early stages — when the child is only slightly overweight — than in the obese range.
Lifestyle changes such as eating a healthier diet and exercising more can have a big impact on a child's weight and overall health. The Centers for Disease Control and Prevention (CDC) recommends that children engage in at least one hour of physical activity every day. That doesn't mean kids have to play a competitive sport or even participate in an organized activity. Physical activity can be as simple as taking the dog for a long walk, biking, running around in the backyard or at a park, dancing, jumping rope or in-line skating. As long as they enjoy the activity and it gets them moving, children can choose whatever activities they like.
Along with encouraging physical activity, parents should limit the time children spend sitting in front of a screen watching television, playing video games or using a computer. The CDC recommends that children have no more than two hours of screen time each day. The American Academy of Pediatrics recommends that children under 2 years old not watch television at all.
Although childhood obesity is a big concern, the opposite can also be hazardous to a child's current and future health. Research has shown that children who have been malnourished during early life and also babies who are born small for their gestational age (the baby's weight is less than would be predicted for the length of time they spent in the womb) are at high risk for developing diabetes and cardiovascular health problems.
If you have concerns about your child's weight, talk to your pediatrician or family physician. Children should never be placed on any type of calorie-restricted or calorie-enhanced diet or exercise program that hasn't been discussed and developed in conjunction with your health care provider.
— Seema Kumar, M.D., Pediatric Endocrinology, Mayo Clinic, Rochester, Minn.