For many Americans, cracking open a diet soda is a small daily treat – fizzy and sweet, with none of the calories or sugar of standard soft drinks.

But a new study suggests that even diet drinks could be turbocharging brain aging. 

Researchers in Brazil honed in on aspartame, a sugar-substitute 200 times sweeter than table sugar found in diet soda and sugar-free desserts. 

In a study of nearly 13,000 adults, the team found people who consumed about the same amount of aspartame found in one can of diet soda experienced 1.6 extra years of cognitive aging compared to those who consumed minimal amounts. 

Even those consuming less than a can's worth of aspartame experienced 1.3 years added years of brain aging.  

And in cognitive tests, this group had more than a 60 percent faster decline in thinking and memory skills, showing a 'clear difference' between those consuming the most and least aspartame. 

As the brain ages, certain structures begin to break down, including the volume of the frontal cortex and protective myelin covering nerve cells. This leads to slowed processing speed and memory, signs of cognitive decline. 

The researchers cautioned, however, that the study cannot prove aspartame directly causes cognitive decline and that conditions like diabetes can contribute to the heightened risk. 

But it does raise concerns about zero-calorie sweeteners that are generally considered healthier than regular sugar. 

'Low- and no-calorie sweeteners are often seen as a healthy alternative to sugar, however our findings suggest certain sweeteners may have negative effects on brain health over time,' Dr Claudia Kimie Suemoto, study author from the University of São Paulo in Brazil, said. 

The study, published in the journal Neurology, researchers followed 12,772 adults with an average age of 52 for about eight years. 

At the beginning, they filled out detailed questionnaires about their food and drink consumption over the past year. Researchers then placed them into three groups based on their total sweetener intake. 

Sweeteners included were aspartame, saccharin, acesulfame K, erythritol, xylitol, sorbitol and tagatose.

The lowest group averaged 20mg a day, while the highest had 191mg daily, about the amount of aspartame in a can of diet soda.

Participants also completed cognitive assessments at the beginning, middle and endpoint of the study. These evaluated verbal skills, working memory, word recall and processing speed. 

After accounting for age, sex and chronic conditions like high blood pressure and heart disease, the researchers found people who consumed the greatest amount of sweeteners experienced a 62 percent faster decline in cognitive skills and 1.6 added years of brain aging.

Those in the middle group had a 35 percent faster decline and 1.3 extra years of brain aging. 

However, age seemed to influence the results, as among those under 60, those who consumed the most sweeteners had faster drops in verbal fluency and overall cognitive performance than those who consumed the least. 

People over 60 did not demonstrate the same association. 

Additionally, diabetes was associated with faster decline, which may be because the condition can damage blood vessels in the brain. 

Tagatose was the only sweetener in the study not associated with cognitive decline. 

'While we found links to cognitive decline for middle-aged people both with and without diabetes, people with diabetes are more likely to use artificial sweeteners as sugar substitutes,' Suemoto said. 

'More research is needed to confirm our findings and to investigate if other refined sugar alternatives, such as applesauce, honey, maple syrup or coconut sugar, may be effective alternatives.'