Childhood obesity is a major concern in the United States, with approximately 17% of the nation's children being overweight or obese. However, new research published by the Centers for Disease Control and Prevention found that such rates are declining in New York City.

Body mass index (BMI) is a measure of body fat based on height and weight. The National Institutes of Health provide a BMI calculator in which you simply enter your height and weight and they give you a BMI category. An underweight individual has a BMI less than 18.5; a person of normal weight has a BMI between 18.5 and 24.9; an overweight individual has a BMI between 25 and 29.9; an obese individual has a BMI between 30 and 30.9; and a severely obese individual has a BMI of 40 or greater.

The category that the CDC research focused on was severe obesity. From the 2006-2007 school year to the 2010-2011 school year, the researchers found that severe obesity rates among New York City K-8 students decreased 9.5% while regular obesity rates decreased 5.5%. They also found that severe obesity was most common among minority, poor, and male children and typically increased with age.

The researchers analyzed 947,765 New York City public school students aged 5 to 14 years. They based their BMI readings on CDC growth charts, using age- and sex-specific BMI percentiles. Their results provide some hope for childhood obesity because New York City is a densely populated area with a diverse group of children. If such rates are decreasing in New York, researchers should be confident they're occurring elsewhere as well. But childhood obesity is still a global problem.

In 2011-2012, the CDC broke down obesity percentages among children and found that 8.4% of 2-5 year-olds were obese, along with 17% of 6-11 year-olds and 20.5% of 12-19 year-olds. Such high statistics (both childhood and adult obesity combined) cost the United States $147 billion in annual medical expenses. If people can work to prevent obesity, the risk for other chronic diseases such as diabetes, stroke, and heart disease will decrease dramatically and improve the health care system.

The study, "Severe Obesity Among Children in New York City Public Elementary and Middle Schools, School Years 2006-07 Through 2010-11," was published in the CDC journal Preventing Chronic Disease.

You can read more about the CDC study on obesity in this Reuters news article.