Studies based on surveys of general populations based on inquiring whether subjects had the “typical” symptoms of GERD, namely heartburn, show that these symptoms are experienced by a large proportion of individuals. A study synthesizing publications surveying general adult samples of Americans found 14 publications reporting GERD symptoms and five covering GERD and other dyspeptic symptoms. The pooled prevalence of GERD symptoms was 24.2 % (95 % confidence interval (CI), [18.2–30.5 %]) and for combination GERD and dyspeptic symptoms it was 35.2 % (95 % CI, [14.8–58.9 %]). The influence of covariates, that is, risk factors for GERD, evaluated as part of most multivariate analyses, is often inconsistent [1]. A survey of 2,973 people in South Australia found that about one-half experience heartburn; 21.2 % at least once a month and 12.4 % at least a few times a week. Of patients reporting symptoms, 25 % self graded the symptoms as moderate or severe and 16.9 % were taking medications for reflux symptoms [2]. However, a Canadian study found the prevalence to be much lower, that is approximately 10–20 % of the population [3]. Prevalence does seem to be affected by ethnicity. A population-based, cross-sectional survey of 1,172 American subjects showed that 50 % of Hispanics experienced heartburn at least monthly, compared to 37 % of Caucasians, 31 % of African Americans, and 20 % of Asians. Asians in the United States had higher rates of symptoms than in the Far East [4].

Another way of evaluating the prevalence of GERD has been to determine how often patients visited medical facilities for assessment and treatment. A study of 134 primary care clinics across six European countries showed that 3.4 % of all visits were for GERD-related reasons. Of these, symptom recurrence following remission was the most common (35.1 %) reason for a primary care visit, while 12.7 % were for persistence of previous symptoms, and 16.2 % had never seen a physician for GERD-related symptoms before [5]. Most primary care physicians can expect to commonly evaluate patients with GERD symptoms.

Other manifestations of GERD are atypical or extra-esophageal symptoms, which may or may not also be associated with the typical symptoms of GERD. In patients with these extra-esophageal symptoms, 81 % had abnormal acid exposure by 48 h Bravo pH monitoring. Most patients had only mild to moderate symptoms with a low prevalence of esophagitis (18 %) or Barrett’s esophagus (0.8 %). It is well described that the degree of esophageal acid exposure, as measured by pH monitoring, cannot be predicted from the presence or absence of typical GERD symptoms [6]. In an evaluation of 18 articles of population-based studies of non-cardiac chest pain, there was an overall prevalence of 13 %, but this varied by geographic location and definition of the disease used (mere presence vs. Rome I or II criteria). There was no difference between men and women, but higher incidences in subjects reporting GERD symptoms and increased as well according to frequency of GERD symptoms [7]. In an analysis from the ProGERD cohort study of patients presenting with heartburn, 32.8 % also had extra-esophageal symptoms. Female gender, age, LA esophagitis grade C or D, duration of GERD symptoms >1 year, and smoking were significantly associated with extra-esophageal symptoms. [8]

There is a significant proportion of individuals with signs of pathologic reflux, but no overt symptoms. In this setting, the definition of “silent” GERD is the presence of esophageal mucosal injury that is typical of GERD found during upper GI endoscopy in individuals who lack the typical or atypical manifestations of GERD [9]. Population-based studies from Sweden, Japan, Taiwan, and Korea have shown that the number of patients with erosive esophagitis but who were asymptomatic varied between 26.4 and 45.3 % [10]. In a group of 594 asymptomatic patients screened with endoscopy in Taiwan, 14.5 % had findings of erosive esophagitis. Male gender (OR 2.32, 95 % CI [1.35–3.98]) and hiatal hernia (OR 4.48, 95 % CI [2.35–89.17]) were risk factors for findings of asymptomatic erosive esophagitis, while a positive CLO test for Helicobacter pylori was protective (OR 0.57, 95 % CI [0.34–0.95]) [11]. Therefore, it is apparent that a significant proportion of people in North American and Europe suffer from some type of GERD. It also appears that although some ethnic groups are more likely to suffer from GERD, there at least some members of all ethnic groups that do.

As with prevalence, the determination of the incidence of GERD depends on the method and what is measured as a sign of GERD. The best data relates to progression of disease in patients already diagnosed with GERD. In a follow-up study of a Swedish general population (the Kalixandra Study), patients with initial endoscopic or histological diagnosis of GERD and nonerosive reflux disease (NERD), 9.7 % of NERD patient progressed to erosive esophagitis, and 1.8 % to Barrett’s esophagus. In patients initially with erosive esophagitis, 13.3 % progress to a more severe grade and 8.9 % to Barrett’s esophagus [12]. In a cohort of 3,894 patients undergoing routine care in Germany, Austria, and Switzerland (the ProGERD study), those who underwent endoscopy and found to have GERD were initially treated with esomeprazole. After 2 years, 25 % of patients who had NERD progressed to LA grade A or B esophagitis and 0.6 % to LA grade C or D esophagitis; 1.6 % of patients who had LA grade A or B esophagitis progressed to LA grade C or D and 61 % regressed to NERD; 42 % of patients with LA grade C or D esophagitis regressed to LA grade A and B, while 50 % regressed to NERD. Of the patient initially on esomeprazole, 22 % had been off medication for at least 3 months. Therefore, it seems that both progression and regression in the severity of esophagitis are common [13]. This same study published a 5-year follow-up of 2,721 patients who completed follow-up and showed only a few patients with NERD or mild/moderate erosive esophagitis progressed to severe forms of erosive esophagitis [14]. Therefore, in patients with mild acid-related mucosal damage, it is not likely that they will progress to more severe forms of mucosal injury as long as they receive appropriate treatment.

To determine the incidence of new GERD-related symptoms, our knowledge generally comes from surveys or administrative data. A survey in Canada determined the adult incidence of GERD to be 4.5–5.4 per 1,000 person–years [3]. This is similar to results from a systematic review of the General Practice Research Database in the United Kingdom, which found the incidence of new diagnoses of GERD to be 4.5 per 1,000 person–years [15]. In another systematic review of published longitudinal studies, 65 % of patients with complicated GERD and 70 % of patients with “defined” GERD had persistent disease on follow-up, whereas only 34 % with infrequent or mild symptoms had persistent symptoms. With the prevalence of GERD in the 10–20 % range and the incidence in the 4.5–19.6/1,000 person–years range, this study suggests that GERD is a disease that persists for at least 18 years [16]. A random sample of 10,000 Danish inhabitants followed for 5 years showed that 22 % had GERD symptoms at inclusion. However, over the 5 years, 43 % had symptom resolution, of which 10 % continued to receive acid reducing medication. The overall incidence of new GERD symptoms was 2.2 %/year [17]. Of course, these are new cases, as to how many individuals who had symptoms of GERD that no longer do now is unknown.

Risk factors for GERD are related to patient’s physiology, behavior factors, and genetic factors. Risk factors for developing gastroesophageal reflux disease include: obesity, smoking, age, parental or family history of gastroesophageal diseases, esophageal stricture, high-cholesterol diet, lung transplantation, and cystic fibrosis—all of which have been commonly associated with GERD [3].

Although age has been associated with GERD, this relationship seems to be more complex. A systematic review of nine population based studies showed no increase in GERD symptom prevalence with age, but in patients with GERD, ageing is associated with more severe patterns of acid reflux and reflux esophagitis. Despite this, symptoms associated with GERD have been shown to become less severe and more nonspecific with age. Therefore, the real prevalence of GERD may well increase with age [18]. However, it may also be that older individuals may simply have minimal or no symptoms of acid reflux, despite pathologic reflux leading even to mucosal damage. However, the evolution of hiatal hernias is clearly associated with age. A meta-analysis of 29 studies showed age >50 years was a definite risk factor for hiatal hernia (OR 2.17, 95 % confidence interval [1.35–3.51]) [19]. This study, however, did not differentiate between symptomatic and asymptomatic hiatal hernia nor for paraesophageal hernias.

The relationship between GERD and gender is also complex. In a South Australian sample of 2,973 individuals from the community and 2,152 patients presenting for antireflux surgery, females were more likely to report heartburn, and with a higher symptom severity. Prevalence of dysphagia was similar from males and females, but dysphagia scores for solid foods were higher in females. A similar proportion of male and female took antireflux medications. Females presenting for antireflux surgery were, on average, 7 years older, had a higher BMI, and higher heartburn and dysphagia scores, while at endoscopy males were more likely to have ulcerative esophagitis and Barrett’s esophagus. The authors concluded that these gender differences may reflect differences in symptom perception [20]. However, with respect to hiatal hernia, the study showed that male gender was a definite risk factor (OR 1.36, 95 % CI [1.10–1.68]) [19].

There appear to be ethnic difference associated with GERD. Evidence from both community surveys and studies of endoscopic findings report esophagitis, hiatus hernia, and Barrett’s esophagus prevalences were lower among Asian and Afro-Caribbean subjects compared to Caucasians. There may also be a north–south gradient in the prevalence of GERD among western countries; that is, GERD may be more common in northern regions compared to southern regions. Studies involving other geographic regions show that GERD may be moderately common in the Middle East and less common in Asia, although the prevalence seems to be increasing in the Far East [21]. In the United States, in a study of an impoverished minority population, waist circumference and smoking were strongly associated with GERD, while overall BMI, waist/hip ratio, and diet were not [22]. Therefore, in some minority populations, the risk factors for GERD are different.

Weight is clearly associated with GERD. Being overweight, obese, or morbidly obese contributes to the development of a variety of esophageal disorders, including hiatal hernia, GERD, Barrett’s esophagus, and esophageal adenocarcinoma [23]. Weight gain increases GERD symptoms and weight loss decreases symptoms [24]. A population-based study in Germany showed a pronounced dose–response relationship between BMI and heartburn occurrence in people without chronic atrophic gastritis, but this was not the case for those with chronic atrophic gastritis [25]. Comparing populations, samples of 3,633 English and 1,483 Swedish people showed that the prevalence of GERD symptoms was twice as common in the English as the Swedish, but obesity (BMI > 30) was also nearly twice as likely, although tobacco smoking was similar [26]. Weight is associated with erosive esophagitis and pathologic acid-reflux related NERD, while patients with functional heartburn or a hypersensitive esophagus tended to be of normal weight. [27] Lastly, with respect to hiatal hernia, individuals with BMI’s > 25 where at increased risk of having a HH (OR 1.92, 95 % CI [1.10–3.39]) [19].

Of particular interest to surgeons are the effects of other disorders on GERD. In a study of Japanese workers with GERD, 6 % of patients were found to have functional dyspepsia or irritable bowel syndrome. Female gender and smoking increased the risk of overlapping GERD with both functional dyspepsia and irritable bowel syndrome [28]. The severity and duration of daytime heartburn and regurgitation were independent risk factors for nocturnal GERD [29]. A diagnosis of depression is also associated with an increased risk of subsequent GERD. The incidence of GERD was 14.2/1,000 person–years in a cohort of patients with depression as compared to 8.3/1,000 person–years in a control group. The use of tricyclic antidepressants increased the risk of GERD (OR 1.71, 95 % CI [1.34–2.20]), while selective serotonin reuptake inhibitors did not [30]. Spinal issues have been recently associated with GERD. A multivariate analysis demonstrated that kyphosis, lumbar lordosis angle, sagittal balance, number of oral drugs taken per day, and back muscle strength had significant effects on the presence of GERD [31]. As these spinal conditions are more common in older individuals, this may, at least partially, explain the increase incidence of GERD with age.

The effects of lifestyle (beyond obesity) and other environmental factors have been shown to have some influence on the occurrence of GERD. Some suggest that smoking, alcohol, dietary fat, or drugs play only a minor role in shaping the epidemiologic patterns of GERD. On a population level, a high prevalence of H. pylori infection is likely to reduce levels of acid secretion and protect against reflux [24]. Obese/overweight people with chronic atrophic gastric actually had a much lower risk of heartburn (OR 0.31, [0.24–0.40]) [25]. On the other hand, in a South Korean population, eradication of H. pylori did not affect the development of reflux esophagitis or GERD symptoms [32].

Stress has been shown to affect GERD as well. The terrorist attacks of September 11, 2001 have resulted in several unique health issues, one of which is GERD. Among individuals exposed to the terrorists attacks at the World Trade Center, the cumulative incidence of GERD symptoms was 20 %, and occurred more often in individuals suffering from post-traumatic stress disorder (24 %), asthma (13 %), or both (36 %), compared with neither (8 %). The authors concluded that GERD symptoms may be accentuated in the presence of asthma or PTSD [33]. This event and its aftermath may help shed light on the relation of patient-perceived symptoms and concomitant psychoemotional disorders in GERD [34].

Risk factors for GERD-related disorders need to be organized into those which truly increase the risk of pathologic acid reflux, those which increase the risk of hiatal hernia, those which increase the risk of erosive esophagitis, and those with increase the perception of GERD-like symptoms. The later can be further divided into the typical and atypical (extra-esophageal) symptoms of GERD. Table 3.2 summarizes the previously discussed risks factors in this manner.