The average waist circumference of American adults has increased from 1999 through to 2012, according to a new study.

Intra-abdominal fat is measured through waist circumference, which gives health care practitioners a good indication of a person’s risk of developing certain health conditions related to obesity. Abdominal obesity is defined as a waist circumference over 40.2 inches in men and over 34.6 inches in women.

Over one-third of the adult population in the U.S. are obese, which raises concerns over the increased risk of medical conditions associated with obesity, including heart disease, diabetes, and cancer. The medical cost associated with obesity in the U.S. was $147 billion in 2008, placing a heavy burden on health care.

Earl S. Ford, M.D., M.P.H., of the U.S. Centers for Disease Control and Prevention, Atlanta, and colleagues looked at data from seven cycles of the National Health and Nutrition Examination Survey (NHANES) to identify trends in the average waist circumference of U.S. adults, and the prevalence of abdominal obesity.

The overall average waist circumference increased significantly, from 37.6 inches in 1999 to 38.8 inches by 2012.

“Our results support the routine measurement of waist circumference in clinical care consistent with current recommendations as a key step in initiating the prevention, control, and management of obesity among patients,” said Ford in a statement.

The findings of the study are published in JAMA.