New observational research hints that regular consumption of sweetened beverages, particularly diet soda, may raise the risk for depression in adults, while drinking coffee may protect against depression.

"Our research suggests that cutting out or down on sweetened diet drinks or replacing them with unsweetened coffee may naturally help lower your depression risk," Honglei Chen, MD, PhD, from the National Institutes of Health, Research Triangle Park, North Carolina, said in a statement.

In an email to Medscape Medical News, Dr. Chen emphasized, however, that the biological mechanisms behind the associations "are not well-understood" and "more research is needed to confirm these findings."

Dr. Chen will present the research at the upcoming American Academy of Neurology 65th Annual Meeting in March.

Beverages and Depression

"A few earlier studies reported that coffee consumption was associated with fewer suicides," Dr. Chen told Medscape Medical News. "Last year, the Nurses' Health Study reported that coffee consumption was associated with lower risk of depression. To the best of our knowledge, our study is the first prospective study on sweetened beverages and depression," Dr. Chen said.

The study team prospectively evaluated intake of sweetened beverages, coffee, and tea in relation to depression among 263,925 US adults aged 50 to 71 years at the outset. Beverage consumption was assessed in 1995-1996. In 2004-2006, a total of 11,311 participants reported being diagnosed with depression.

All analyses, Dr. Chen said, were based on "extreme" exposures, which they defined as 4 or more cups or cans per day versus nondrinkers.

The results showed that people who drank 4 or more cups or cans of soda per day were 30% more likely to develop depression than those who drank no soda, whereas those who reported this level of intake of fruit punch were about 38% more likely to develop depression. People who drank 4 cups of coffee per day were about 10% less likely to develop depression than those who drank no coffee.

Table 1. Beverage Intake and Risk for Depression With 4 or More Cans or Cups per Day vs None

Beverage OR (95% CI) Soda 1.30 (1.17 - 1.44) Fruit punch 1.38 (1.15 - 1.65) Coffee 0.91 (0.84 - 0.98)

All P for trend < .0001. CI, confidence interval; OR, odds ratio.

The risk appeared to be greater for people who drank 4 or more cups or cans of diet soda, fruit punch, or iced tea, as opposed to the same amount of regular soda, fruit punch, or iced tea.

Table 2. Depression Risk With Diet vs Regular Sweetened Drinks (4 or More Cans/Cups per Day vs None)

Beverage OR (95% CI) Soft drinks Diet 1.31 (1.16 - 1.47) Regular 1.22 (1.03 - 1.45) Fruit punch Diet 1.51 (1.18 - 1.92) Regular 1.08 (0.79 - 1.46) Iced tea Diet 1.25 (1.10 - 1.41) Regular 0.94 (0.83 - 1.08)

"Consistently, constituent-based analyses showed higher depression risk with aspartame intake (ORs between extreme quintiles: 1.36; 95% CI 1.29-1.44) and lower risk with caffeine intake (OR 0.83; 95% CI 0.78-0.89)," the researchers report.

Dr. Chen said the analyses were adjusted for "many socioeconomic and lifestyle factors, and only included cases that reported a diagnosis at least 4 years after the dietary assessment. However, we could not exclude the possibility of confounding by other factors or the possibility that individuals at higher risk for depression were drawn to sweetened drinks."

The study was supported by the National Institutes of Health, the National Institute of Environmental Health Sciences, and the National Cancer Institute. The authors have disclosed no relevant financial relationships.

American Academy of Neurology's 65th Annual Meeting. Abstract 2257. Released January 8, 2013.