New study suggests a connection between soft drinks and depression via the microbiome

A new study involving the German Center for Diabetes Research (DZD) provides strong evidence that sugary drinks affect not only metabolic but also mental health – especially in women. This effect is probably mediated by the sensitive microbiome of the intestine.

As is well known, people who regularly consume sugary drinks not only have an increased risk of obesity, type 2 diabetes, cardiovascular disease and cancer. There is an increasing number of studies that are now showing that soft drinks can also affect mental health. So far, however, it was unclear whether there is a direct relation to major depressive disorder (MDD) and which biological processes might be involved. 

Soft drink consumption associated with higher risk of depression 

To answer these questions, researchers analyzed cross-sectional data from the Marburg-Münster Affective Cohort (MACS). The study examined adults between the ages of 18 and 65 who were recruited from the general population and primary care between 2014 and 2018. The researchers included a total of 932 people, 405 of whom were patients with major depression disorder and 527 were healthy controls. 

The analyses showed a correlation between soft drink consumption and both the diagnosis of depression and the severity of the symptoms. This correlation was particularly pronounced in women: Among them, high consumption was associated with a 17% higher probability of depression (odds ratio 1.167) and more severe symptoms. 

Changes in the microbiome as a key factor 

But how could the effect be conveyed? Here, too, the study provides a possible explanation: In women who regularly drank sugary soft drinks, the researchers found a significantly increased number of bacteria of the Eggerthella genus in the intestine. Earlier studies had shown that Eggerthella is more common in people with depression. The current study now provides the first convincing evidence that this bacterium possibly plays a mediating role – as a biological link between the consumption of soft drinks and the development of depressive symptoms. 

"Our data suggests that the relation between soft drinks and depressive symptoms arises via the influence of the microbiome," says study leader Dr. Sharmili Edwin Thanarajah from the University Hospital Frankfurt and the MPI for Metabolism Research Cologne, an associated partner of the German Center for Diabetes Research (DZD).

Sugary drinks such as cola or lemonade not only contain glucose and fructose, but also numerous additives – including preservatives and artificial sweeteners. This combination can disturb the delicate balance in the intestinal microbiome. Inflammation-promoting bacteria are favored, while the production of protective short-chain fatty acids decreases. Animal studies show that such changes can trigger inflammatory processes in the nervous system and thus increase depressive behavior. 

It is striking that this correlation appears to be sex-related. In men who regularly consumed soft drinks, the researchers found neither an increase in Eggerthella nor a correlation with depressive symptoms. It is still unclear why this effect only occurs in women. Hormonal differences or sex-related reactions of the immune system possibly play a role. 

The microbiome as a therapeutic target? 

"The study results open up new perspectives for the prevention and treatment of depressive disorders," comments DZD researcher Rachel Lippert from the German Institute of Human Nutrition Potsdam-Rehbrücke (DIfE). "Microbiome-based approaches – such as targeted nutritional therapies or probiotic strategies – might help to effectively alleviate depressive symptoms in the future." 

The researchers therefore argue that the influence of nutrition on mental health should be more strongly integrated into educational campaigns, care concepts and prevention programs. 

Changes in the microbiome can be influenced by diet – and are therefore a potential therapeutic target." 

Dr. Sharmili Edwin Thanarajah, University Hospital Frankfurt 

"Even small adjustments in consumer behavior might have a big impact – especially when considering the widespread consumption of soft drinks."