Drinking more than four sweetened beverages a day doesn’t appear to be good for one’s mood, especially diet soda, a study by the U.S. National Institutes of Health found.

In a study of more than 200,000 older adults, those who drank more than four cans of soda a day had a 30 per cent greater risk of depression than those who consumed none. The same amount of fruit punch was tied to a 38 per cent higher risk, according to research released today by the American Academy of Neurology. The risk was even greater for people who consumed diet drinks, whether soda, punch or iced tea.

The study, one of the first to look at sweetened beverages and depression, doesn’t explain the connection, so it’s still unknown how the drinks may be tied to mental health, said Honglei Chen, one of the study’s researchers. One theory is that the drinks have been linked to diabetes and obesity, which in turn can lead to the mood disorder, he said.

“Although our results are preliminary, consumption of sweetened beverages should be reduced as they have been linked to other adverse health outcomes,” said Chen, an investigator in the Epidemiology Branch of the National Institute of Environmental Health Sciences in Research Triangle Park, North Carolina, part of the NIH, in a Jan. 7 email.

More research is needed to confirm the findings, Chen said. Today’s results will be presented at the American Academy of Neurology’s annual meeting in San Diego in March.

Depression Diagnoses

Researchers in the study looked at 263,925 U.S. adults ages 50 to 71. They assessed the types of beverages they consumed in 1995 to 1996. About 10 years later, the participants were asked if they had been diagnosed with depression.

About 350 million people worldwide suffer from depression, according to the World Health Organization. In the U.S., the U.S. Centers for Disease Control and Prevention estimate that one in 10 adults report having the disorder.

The researchers didn’t examine specific chemicals in the drinks like artificial sweeteners to determine which ingredients in the beverages may trigger the disease, Chen said.

One beverage, though, had an opposite effect. Coffee was found to lessen a person’s chance of developing the mood disorder.

People who drank four cups of coffee each day had about a 10 per cent lower risk of developing depression than those who didn’t consume coffee, the research found. Chen said coffee contains large amounts of caffeine, which is a brain stimulant.