Regularly drinking diet soda could impact waist size, say the authors of a study linking calorie-free colas to greater abdominal obesity in adults 65 years of age and older.

The study, which was published in the Journal of American Geriatrics, is among the first to focus on the effect of artificial sweeteners in an aging population.

What's more, chronic diet soda consumption could increase the risk of metabolic syndrome, which is the co-occurrence of risk factors that contribute to cardiovascular disease.

"The burden of metabolic syndrome and cardiovascular disease, along with healthcare costs, is great in the ever-increasing senior population," says lead author Sharon Fowler, MPH, from the University of Texas Health Science Center at San Antonio.

According to the World Health Organization (WHO), 1.9 billion adults were overweight -- defined as having a body mass index (BMI) of 25 or more -- in 2014 and 600 million of them were classified as obese with a BMI of 30 or more.

This is more than double the existing cases of obesity the WHO counted in 1980.

Artificial sweeteners such as saccharin, aspartame and sucralose are now coming under fire, for studies suggest consumption of these products has increased in the past 30 years -- along with the number of obesity cases.

Working with 749 individuals of Mexican-American and European-American descent aged 65 or older when the San Antonio Longitudinal Study of Aging (SALSA) began in the mid-1990s, the researchers collected data for 9.4 years.

They tracked participants' diet soda intake, and measured waist circumference, height and weight four times during the course of the study, including three follow-ups.

Data was adjusted for multiple potential confounders and the study says that abstainers had an average waist circumference increase of 0.77 cm at each follow-up; occasional users measured in at 1.76 cm; and daily diet soda drinkers at 3.04 cm.

Over the course of the entire study, waist circumference had increased among abstainers by 0.80 in, among occasional drinkers by 1.83 in and 3.16 in for daily diet soda drinkers.

"The SALSA study shows that increasing diet soda intake was associated with escalating abdominal obesity, which may increase cardiometabolic risk in older adults," says Fowler.

Older individuals are advised to curb their consumption of artificially sweetened drinks, especially if they are at high cardiometabolic risk.