Psychobiotics were previously defined as live bacteria (probiotics) which, when ingested, confer mental health benefits through interactions with commensal gut bacteria. We expand this definition to encompass prebiotics, which enhance the growth of beneficial gut bacteria. We review probiotic and prebiotic effects on emotional, cognitive, systemic, and neural variables relevant to health and disease. We discuss gut-brain signalling mechanisms enabling psychobiotic effects, such as metabolite production. Overall, knowledge of how the microbiome responds to exogenous influence remains limited. We tabulate several important research questions and issues, exploration of which will generate both mechanistic insights and facilitate future psychobiotic development. We suggest the definition of psychobiotics be expanded beyond probiotics and prebiotics to include other means of influencing the microbiome.

Objectives To identify risk factors for and the consequences (several adverse perinatal outcomes) of physician-diagnosed major depression during pregnancy treated in specialised healthcare. Design A population-based cross-sectional study. Setting Data were gathered from Finnish health registers for 1996–2010. Participants All singleton births (n=511 938) for 2002–2010 in Finland. Primary outcome measures Prevalence, risk factors and consequences of major depression during pregnancy. Results Among 511 938 women, 0.8% experienced major depression during pregnancy, of which 46.9% had a history of depression prior to pregnancy. After history of depression, the second strongest associated factor for major depression was fear of childbirth, with a 2.6-fold (adjusted OR (aOR=2.63, 95% CI 2.39 to 2.89) increased prevalence. The risk profile of major depression also included adolescent or advanced maternal age, low or unspecified socioeconomic status (SES), single marital status, smoking, prior pregnancy terminations, anaemia and gestational diabetes regardless of a history of depression. Outcomes of pregnancies were worse among women with major depression than without. The contribution of smoking was substantial to modest for small-for-gestational age newborn (<−2 SD below mean birth), low birth weight (<2500 g), preterm birth (<37 weeks) and admission to neonatal intensive care associated with major depression, whereas SES made only a minor contribution. Conclusions Physician-diagnosed major depression during pregnancy was found to be rare. The strongest risk factor was history of depression prior to pregnancy. Other associated factors were fear of childbirth, low SES, lack of social support and unhealthy reproductive behaviour such as smoking. Outcomes of pregnancies were worse among women with major depression than without. Smoking during pregnancy made a substantial to modest contribution to adverse outcomes associated with depression during pregnancy.

Objectives To study how reproductive risks and perinatal outcomes are associated with postpartum depression treated in specialised healthcare defined according to the International Classification of Diseases (ICD)-10 codes, separately among women with and without a history of depression. Design A retrospective population-based case–control study. Setting Data gathered from three national health registers for the years 2002−2010. Participants All singleton births (n=511 422) in Finland. Primary outcome measures Prevalence of postpartum depression and the risk factors associated with it. Results In total, 0.3% (1438 of 511 422) of women experienced postpartum depression, the prevalence being 0.1% (431 of 511 422) in women without and 5.3% (1007 of 18 888) in women with a history of depression. After adjustment for possible covariates, a history of depression was found to be the strongest risk factor for postpartum depression. Other strong predisposing factors for postpartum depression were fear of childbirth, caesarean birth, nulliparity and major congenital anomaly. Specifically, among the 30% of women with postpartum depression but without a history of depression, postpartum depression was shown to be associated with fear of childbirth (adjusted OR (aOR 2.71, 95% CI 1.98 to 3.71), caesarean birth (aOR 1.38, 95% CI 1.08 to 1.77), preterm birth (aOR 1.65, 95% CI 1.08 to 2.56) and major congenital anomaly (aOR 1.67, 95% CI 1.15 to 2.42), compared with women with no postpartum depression and no history of depression. Conclusions A history of depression was found to be the most important predisposing factor of postpartum depression. Women without previous episodes of depression were at an increased risk of postpartum depression if adverse events occurred during the course of pregnancy, especially if they showed physician-diagnosed fear of childbirth.

Study Design. Prospective clinical study. Objective. To investigate the effect of depressive symptoms on the surgery outcome on 2-year follow-up among lumbar spinal stenosis (LSS) patients. Summary of Background Data. Previous research has suggested an association between preoperative depressive symptoms and a poorer surgery outcome among LSS patients. There have been no previous studies on the effect of depressive symptoms on the surgery outcome at the 2-year postoperative phase. Methods. A total of 96 patients (mean age, 62 years) with symptomatic LSS underwent decompressive surgery. They completed the same set of questionnaires before surgery and 3 months, 6 months, 1 year, and 2 years after surgery. Depression was assessed with the 21-item Beck Depression Inventory (BDI). Physical functioning and pain were assessed with the Oswestry Disability Index, the Stucki Questionnaire, self-reported walking ability, he visual analogue scale, and pain drawing. Comparisons were made according to depression status. Logistic regression analysis was used to examine the factors associated with a poorer surgery outcome on 2-year follow-up. Results. After surgery, the patients with continuous depression showed poorer improvement in symptom severity, the disability score, and walking capacity than the patients who did not have depression in any phase. In those patients who recovered from depression, the postoperative improvement resembled that of the constant normal mood group. In regression analyses, an independent association was detected between high preoperative BDI scores and 2-year disability and symptom severity. Strong independent associations were seen between depression burden (the sum of preoperative, 3-month and 6-month BDI scores) and 2-year disability, symptom severity, and poor walking capacity. Conclusion. The patients with a normal mood and those who recovered from depressive symptoms enjoyed the most favorable outcome. Depressive symptoms interfere strongly with the ability of patients to obtain an optimal surgery outcome. Treatment models including the assessment and treatment of depression are encouraged.