Functional gastrointestinal disorders (FGIDs) are disorders of gut-brain interaction (DGBI). DGBI are characterized by persistent and recurring gastrointestinal (GI) symptoms that are a result of abnormal functioning of the GI tract and not associated with obvious structural or biochemical abnormalities. DGBI include any combination of the following: motility disturbance, visceral hypersensitivity, altered mucosal and immune function, altered gut microbiota, and altered central nervous system processing [1]. The Rome IV criteria provide a widely accepted diagnostic taxonomy containing 6 primary DGBI domains for adults including: 1.) Esophageal Disorders, 2.) Gastroduodenal Disorders, 3.) Bowel Disorders, 4.) Centrally Mediated Disorders of GI Pain, 5.) Gallbladder and Sphincter of Oddi Disorders, and 6.) Anorectal Disorders. Each DGBI is classified based on the patient’s report of symptom type and severity. One of the most studied domains is Bowel Disorders. This domain is further separated into 6 subcategories including an irritable bowel syndrome (IBS) subcategory, the most frequently diagnosed GI disorder [2]. Some have criticized the Rome IV criteria and prefer to describe DGBI as a “spectrum of chronic GI disorders with combinations of symptoms … existing on a continuum rather than as discrete disorders” [3]. Multiple studies support this dimensional approach, providing scientific evidence that patients can transition from one disorder to another and may receive multiple diagnoses [2,3,4,5]. Based on recent scientific knowledge regarding the multifactorial etiology of DGBI and the non-specific and stigmatizing nature of the term “functional,” the Rome IV Foundation has recommended that FGIDs be referred to as DGBI. Nonetheless, since the acronym FGID has been embedded in gastroenterological studies, our literature review will remain consistent with terminology used by previous authors’ empirical work.
A study within a general US adult population (n = 71,812, ages 18–65) used the National Institutes of Health (NIH) Patient-Reported Outcomes Measurement Information System GI scales (PROMIS-GI) to evaluate the prevalence of eight overarching GI symptom domains: abdominal pain, bloating/gas, bowel incontinence, constipation, diarrhea, swallowing, reflux, and nausea/vomiting [6]. Sixty-one percent of their sample endorsed at least one symptom within the past 7 days. Of those, 58.4% indicated they experienced two or more symptoms concurrently. A third of their sample population experienced reflux/heartburn, making it the most prevalent symptom. One quarter reported abdominal pain and a fifth of their participants’ experienced bloating, diarrhea, and constipation. This study included emerging adults in their population sample, finding that over 54% (n = 6954) reported the occurrence of at least 1 GI symptom within the past week. However, further descriptions of GI symptoms within emerging adults were not provided.
Generally, emerging adults (age 18–25) are viewed as a physically healthy cohort [7] and consequently often overlooked in current GI health research. More recent epidemiological studies suggest that FGIDs are increasing in emerging adults [8,9,10]. As many as 65% of emerging adults are experiencing symptoms [11] and approximately one third are seeking medical care [12]. Of all the FGID syndromes, the most studied in emerging adults is IBS. According to the American College Health Association (ACHA) National College Health Assessment II national survey for the Fall 2017 semester, 3.2% of the undergraduate students surveyed (n = 5789) had been diagnosed by a healthcare professional of having IBS [13]. Another study evaluated the frequency of self-reported IBS symptoms in college students demonstrating that 34% of the sample (n = 508, mean age: 22.0+/− 2.8 yrs) experienced clinical levels [12]. This previous research demonstrated a high incidence of IBS in the emerging adult population but is limited in that it does not capture a broader range of general GI distress or other clinical symptomatology.
Emerging adulthood marks the shift from being dependent on a care provider to taking independent responsibility for seeking medical care [14]. Research indicate this population have decreased adherence to medication and attend fewer physician appointments [9, 15]. Furthermore, this period establishes fundamental health and self-care behaviors that carry forward into adulthood [16, 17]. Adverse health behaviors have been observed in the amount of sleep, cigarette use, drinking, exercise, and eating habits of emerging adults [15, 17, 18].
The current understanding of DGBI are supported by a biopsychosocial model [1], which places equal value in researching the patient’s reported experience of illness with the physical indicators of disease [19]. Additionally, researchers have identified a bi-directional communication pathway between the central nervous system and the GI tract, termed the gut-brain axis [1, 20]. The gut-brain axis suggests that changes in either the central nervous system or gut can disrupt the balance of the other. Therefore, psychosocial factors impacting the gut-brain axis could enhance the risk of developing GI symptoms, symptom severity, and affecting treatment outcomes [1, 20]. At present, the psychosocial factors involved include but are not limited to environmental, cultural, and psychosocial factors, including the composition of an individual’s gut microbiome, diet, and nutrition [20].
An environment with chronic and high levels of life stress has proven to be one of the strongest factors for developing FGIDs [19]. Emerging adults are especially susceptible to chronic stress as they transition into adulthood [21]. Stress provoking environments for emerging adults include attending college and adjusting to new social settings [22]. Consequently, the inability to properly cope with chronic stress frequently results in depression and maladaptive eating behaviors in emerging adults [17]. According to the latest Rome IV overview, psychosocial factors associated with the gut-brain axis that interact with the development and severity of FGIDs include mood disorders (depression and suicide ideation), anxiety disorders, somatization, and cognitive-affective processes [20].
Anxiety disorders are closely associated with the onset and duration of FGIDs. Studies have found that general anxiety disorders (GAD) are directly associated with the biological stress response processes, and as a result, can alter pain tolerance and GI motility [20]. In a sample of 604 college students (age = 20.9 ± 1.5 years), 36.9% endorsed IBS symptoms, according to Rome III criteria, with 13.9% presenting with both IBS and GAD [23]. Additionally, it has been argued that anxiety disorders have a greater impact on the risk, comorbidity, and outcome of IBS than depression [24]. The prevalence of depression was found in 30% of medical-seeking patients presenting with FGIDs [25] with 15 to 38% of clinical patients with IBS presenting with suicidal ideation [26], while anxiety disorders were revealed in 30–50% of clinical patients with FGIDs [20]. Only a few studies have evaluated GI symptoms and depression in an emerging adult population. One study with emerging adults found that 13.6% (n = 773) of their sample reported moderate to major depression [27]. The comorbidity of depression and anxiety can be associated with poor health outcomes and inferior quality of life [28, 29]. Experiencing chronic GI symptoms can also result in consequences for overall health-related quality of life (HRQoL), i.e. “… one’s general well-being, daily function status, and sense of control over the symptoms” (p. 1273) [1]. Studies have shown that HRQoL was significantly lower in individuals with IBS than healthy individuals [30]. However, studies concerned with health outcomes in emerging adults are very limited.
Problem statement: defining patterns of GI symptoms in young adults
The purpose of this study was to identify common GI symptom groups within emerging adults based on the National Institutes of Health (NIH) Patient-Reported Outcomes Measurement Information System GI symptom scales (PROMIS-GI) which is freely available at www.healthmeasures.net. A secondary goal was to relate the emergent groups to the Rome IV DGBI symptom domains. A tertiary goal was to identify psychosocial comorbidities within these groups. The use of the PROMIS-GI scales afforded this study with a means to measure a broad range of GI functioning and symptom levels within a general emerging adult population group. To date, there is no comprehensive study exploring general GI functioning in the emerging adult population using the PROMIS-GI symptom scales. To identify common GI symptom patterns, a latent class analysis approach was employed. Latent class analysis (LCA) is a statistical method that allows the researcher to use a set of observed variables to identify hidden but meaningful patterns resulting in homogenous groups of participants (latent classes) [31]. Ideally these groups would represent symptom profiles corresponding to different DGBI diagnostic categories.