An increasing body of research has demonstrated a strong connection between the gut microbiome and mood disorders.1 Moreover, an unhealthy diet is increasingly shown to be a risk factor for depression, with the gut microbiota as a “key factor mediating the link between diet and depressive illness.”1 The communication between the gut and the brain via gut microbiota is called the “microbiome-gut-brain axis.”1
Probiotics have been defined by the Food and Agriculture Organization of the United Nations as “live microorganisms that, when administered in adequate amounts, confer a health benefit on the host.”2 This benefit is accomplished through altering the host’s microflora.3 Since gut dysbiosis appears to be a risk factor for depressive illness, modifications to the gut microbiota with probiotics may have a beneficial impact on mood. This association has been supported by animal data suggesting that exposing mice to probiotics may reduce anxiety- and depression-related behaviors.4 The term “psychobiotics” has been coined to refer to probiotics “that, when ingested in adequate amounts, work on the brain/gut axis to produce health benefits for suffers of depression.”5
A recent large, population-based, cross-sectional analysis of data from the National Health and Nutrition Survey (NHANES) was conducted by Cepeda et al to assess the association of probiotics with depression.3 The researchers included 18,019 subjects, age 18 years or older, who responded to two 24-hour dietary recall interviews and to a depression questionnaire.
Probiotic exposure was assessed through the NHANES dietary interview, which included detailed food and dietary supplement intake information to estimate the types and amounts of food and beverages consumed during the 24-hour period prior to the interview.
Types of probiotic foods included were yogurt, buttermilk, kefir milk, and kimchi. The researchers did not include food that might have undergone heat processing, which destroys live cultures, or foods such as frozen yogurt that do not consistently contain live probiotics. In addition to foods, they included a total of 152 different types of probiotic supplements. Depression was measured using the Patient Health Questionnaire (PHQ-9). Moderate or more severe depression was defined as a score of ≥10, while mild or more severe depressive symptoms was defined as a score of ≥5.