Short-chain fatty acid-producing psychobiotics in mood disorders: mechanistic insights into the microbiota-gut-brain axis.

Head and neck cancer (HNC) represents a heterogeneous group of malignant tumors arising in the oral cavity, oropharynx, nasopharynx, hypopharynx, larynx, major salivary glands, nasal cavity, and paranasal sinuses []. In the USA, HNC accounts for approximately 4% of all cancers, with an estimated 48,200 new cases in males and 17,430 in females diagnosed in 2020 []. Treatment is typically multimodal, most commonly involving surgery, radiotherapy, and chemotherapy []. Despite advances in oncological management, the majority of patients experience significant treatment-related sequelae. These include physiological impairments such as dysphagia, dysphonia, xerostomia, temporomandibular joint ankylosis, neck stiffness, and compromised nutritional and gastrointestinal function []. In addition to physical complications, patients are at elevated risk of psychological distress, particularly depression and anxiety, which further contribute to deterioration of overall quality of life []. Informal caregivers (ICs)—relatives, friends, or neighbors who provide unpaid care driven by personal bonds rather than professional duty []—play an essential role in supporting patients with HNC. Across the continuum of care, from diagnosis through rehabilitation, caregivers are often responsible for assisting with activities of daily living (e.g., feeding and bathing) []. Their responsibilities frequently extend to complex tasks such as managing dysphagia and nutritional intake, providing postoperative wound care, and ensuring adherence to medications for pain management and recovery []. Beyond physical support, caregivers are also critical in addressing the psychological and social challenges associated with HNC. Altered appearance and speech impairments frequently lead to social withdrawal and heightened psychological distress among patients. In this context, caregivers play a central role in facilitating emotional adjustment, offering sustained psychosocial support, and helping to alleviate anxiety and depression []. The psychological well-being of ICs themselves is profoundly affected by the demands of caregiving, making their mental health a central concern. Many caregivers report unmet needs for support when confronted with the challenges of cancer care []. Caregiving frequently disrupts daily life, with significant alterations to household routines, occupational responsibilities, and social relationships. In prioritizing the needs of patients, caregivers often neglect their own health and well-being [] Depression and anxiety are the most common psychological sequelae, with prevalence rates ranging from 52 to 94% across studies []. Importantly, psychological burden is often more frequent and severe among caregivers than among patients themselves. Gender differences are evident, with female caregivers consistently reporting higher levels of anxiety []. Moreover, caregiver distress is closely interrelated with patient well-being, with anxiety and depression frequently showing a correlation between the two [].