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References: Anxiety, Depression, and the Gut

  1. Prevalence of symptoms of anxiety and depression in patients with inflammatory bowel disease: a systematic review and meta-analysis - Barberio B, et al. Lancet Gastroenterology & Hepatology, 2021 - The 77-study, 30,118-adult meta-analysis behind this chapter's main numbers and its "How to read a gut-brain claim" box. The abstract gives the overall rates and the active-versus-inactive comparison.

  2. Systematic review with meta-analysis: the prevalence of anxiety and depression in patients with irritable bowel syndrome - Zamani M, Alizadeh-Tabari S, Zamani V. Alimentary Pharmacology & Therapeutics, 2019 - Pools studies of people with IBS and finds anxiety and depression symptoms at about three times the odds seen in healthy people.

  3. Systematic review with meta-analysis: anxiety and depression in children and adolescents with inflammatory bowel disease - Stapersma L, et al. Alimentary Pharmacology & Therapeutics, 2018 - The teen-focused meta-analysis (28 studies, average age 14.3) discussed in Section 11.4, with its cautions about different questionnaires and cutoffs.

  4. The brain-gut pathway in functional gastrointestinal disorders is bidirectional: a 12-year prospective population-based study - Koloski NA, et al. Gut, 2012 - A 12-year Australian cohort study showing that anxiety predicts new gut disorders and gut disorders predict later anxiety and depression. A classic example of a cohort study testing direction.

  5. Bi-directionality of brain-gut interactions in patients with inflammatory bowel disease - Gracie DJ, Guthrie EA, Hamlin PJ, Ford AC. Gastroenterology, 2018 - A 2-year cohort of 405 adults with IBD showing that active disease predicts later anxiety and anxiety predicts later flares. Source for Section 11.6.

  6. Inflammatory markers in depression: a meta-analysis of mean differences and variability in 5,166 patients and 5,083 controls - Osimo EF, et al. Brain, Behavior, and Immunity, 2020 - Free full text of the meta-analysis showing that, on average, people with depression have higher inflammation markers. Useful for weighing the inflammatory depression theory.

  7. Transferring the blues: depression-associated gut microbiota induces neurobehavioural changes in the rat - Kelly JR, et al. Journal of Psychiatric Research, 2016 - One of the two microbiota transfer studies in Section 11.8. A good example of an animal experiment that tests cause but can't prove what happens in people.

  8. The neuroactive potential of the human gut microbiota in quality of life and depression - Valles-Colomer M, et al. Nature Microbiology, 2019 - A large human study linking certain gut bacteria to depression and quality of life, while stressing the importance of confounders. Observational, so it can't show direction.

  9. Efficacy of psychological therapies in people with inflammatory bowel disease: a systematic review and meta-analysis - Riggott C, Mikocka-Walus A, Gracie DJ, Ford AC. Lancet Gastroenterology & Hepatology, 2023 (open access) - Updates the group's 2017 analysis (Gracie et al.) to 25 randomized trials: small short-term benefits for anxiety, depression, stress, and quality of life in quiet IBD, a small lasting benefit for depression scores, and no effect on disease activity. Source for the integrated care evidence in Section 11.11.

  10. Unmet Need for Mental Health Services Among High School Students Experiencing Persistent Feelings of Sadness or Hopelessness: Youth Risk Behavior Survey, United States, 2025 - Kiplagat SJ, et al. (CDC), MMWR Supplements 75(1):35-43, October 15, 2026 - The newest national survey: 33.3% of US high school students reported persistent sadness or hopelessness in 2025, and about 3 in 10 of those students (28.8%) reported an unmet need for counseling or therapy.

  11. Teen Depression: More Than Just Moodiness - National Institute of Mental Health (NIMH) - A short, free guide for teens on the signs of depression, how it is treated, and how to get help from a trusted adult, a doctor, or the 988 Lifeline.

  12. Get Help - 988 Suicide & Crisis Lifeline - How to reach the free, confidential, 24/7 Lifeline by call, text, or chat, including options in Spanish. Bookmark it, for yourself or for a friend.