A new study conducted by the U.S. Centers for Disease Control and Prevention found that the average waistline of Americans has increased by an inch in the span of three years. 

CDC medical officer Dr. Earl Ford worked with his colleagues to review data collected by the National Health and Nutrition Examination Survey (NHANES) involving at least 33,000 men and women, aged 20 years old and above.

Results of the analysis showed that between 1999 and 2012, the average waist size of Americans increased from 37.6 inches to 38.8 inches.

The researchers were surprised that the waistlines of the American population are still increasing; about 25 percent of American adults are classified as obese, but 54 percent of the participants were abdominally obese during the study period.

Increasing waistlines are more prevalent for women, at 1.5 inches on average compared to men who were less than an inch.

"Waists are still expanding in the U.S., and particularly so among women," Dr. Ford told Healthday News.

Waistlines that are wider than 40 inches for males and 35 inches for females are classified as abdominal obesity. A wide waistline is an enormous risk factor for developing diabetes, heart disease, and other ailments. An earlier study showed that men with 43-inch and above waistlines were 50 percent more likely to die young compared to those with smaller waistlines. Women with waistlines of at least 37 inches, on the other hand, had 80 percent of a higher risk of death.

Researchers believe sleep deprivation and exposure to chemicals such as endocrine disruptors may be part of the reason behind America's increasing waistlines. But this spike was not the observed among children and teens, whose measurements remained at 18 percent between 2003 and 2012.

Further details of the CDC study were published in the Sept. 17 issue of Journal of American Medical Association.