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Khek-Yu
HO, Department of Medicine, National
University of Singapore, Singapore
Correspondence to: Dr Khek-Yu
HO, MBBS (Syd Hons 1) FRACP FAMS,
Department of Medicine, National University Hospital, Lower Kent
Ridge Road, Singapore 119074
Telephone:
+65-7724353,
Fax. +65-7794112
Email. mdchoky＠nus.edu.sg
Received:
1998-12-30
Subject
headings: gastroesophageal reflux;
esophagitis; Barrett′s
esophagus; hiatus hernia; Helicobacter pylori; gastric acid
Ho KY. Gastroesophageal reflux disease is
uncommon in Asia: evidence and possible explanations. World J Gastroentero, 1999;5(1):4-6
DEFINITIONS
Gastroesophageal reflux that predisposes an-indivi_dual to the
risk of physi cal complications, or produces symptoms leading to
significantly impaired quality of life, is termed gastroesophageal
reflux disease (GERD)［1］.
Clinically, GERD encompasses a broad spectrum of separate, though
related conditions that a re sometimes conveniently grouped under
two broad categories: endoscopic esophag itis and endoscopy negative
reflux disease. Endoscopic esophagitis is considered to be present
when there is endoscopically visible breakage of the mucosa［2］,
regardless of whether the patient has symptoms. The term “endoscop
ic negative reflux disease”
refers to GERD that is not associated with Barrett ′s
esophagus or esophageal mucosal breaks. It includes such conditions
as esoph ageal mucosal acid sensitivity, which is symptomatic reflux
induced by acid refl ux and proven by objective means; abnormal
esophageal acid exposure, which is ex cessive acid reflux confirmed
by objective measures; and reflux type symptoms ( heartburn and/or
acid regurgitation) that clearly dominate the patient′s
comp laints［3］.
Barrett′s
esophagus is the eponym applied to the columnar ep ithelium-lined
lower esophagus that is acquired as a consequence of chronic gas
troesophageal reflux［4］.
Hiatus hernia, on the other hand, has been defi ned as a
displacement of the gastric mucosa 1.5cm or more above the diaph
ragmatic hiatus［5］.
EVIDENCE FOR A LOW PREVALENCE OF GERD IN ASIA
Prevalence of reflux-type symptoms in general population
Until recently, there has been no systematic study on the
prevalence of reflux type symptoms in the general population of
Asia. A cross-sectional survey of a race stratified sample of adults
in a Singaporean town provides some of the fir st evidences, that
reflux-type symptoms are uncommon in the East［6］.
Of 696 persons evaluated, only 2% had heartburn and/or acid
regurgitation for more than once a month. This prevalence is much
lower than those (29%-44%) of Wester n populations［7,8］.
Prevalence of GERD in pregnant women
The individuals with the highest prevalence of heartburn are
often said to be pregnant women. A prospective study, using a
reliable questionnaire, on a consecutive series of pregnant women in
Singapore, provides the second piece of evidence that reflux-type
symptoms are uncommon among Asians［9］.
Of the 35 pregnant women evaluated, 23% had heartburn some time
during their pregnancy. This p ercentage is lower than those
(48%-96%)repor_ted previously in the West［10,11］.
Frequency of GERD in outpatient clinics
In a large clinical series from Singapore, Kang et al
from Singapore noted a 2% frequency of GERD among 2141 consecutive
patients investigated［12］.
The diagnosis of GERD was established on the basis of an abnormal
endoscopy, a positive acid perfusion test and/or an abnormal 24-hour
pH monitoring. The fre quency was lower as compared with a similar
series from the West［13］.
Prevalence of endoscopic esophagitis
Very few epidemiological data on reflux esophagitis in
Asians are available in t he literature. However, Chang et al
found 5% with reflux esophagitis［14］
in an endoscopic series of 2044
patients who underwent self paid medical c heck-ups. Esophagitis,
when present, was often mild. The prevalence of endoscop ic
esophagitis among symptomatic subjects has not been well studied and
the available data are conflicting. In a study from Taiwan, a 15%
prevalence of erosive esophagitis was found in 455 consecutive
patients evaluated for various upper gastrointestinal tract symptoms［15］.
Most of the patients presente d with mild esophagitis. The expected
high frequency of erosive esophagitis is not supported by other
endoscopic series from Asia. Erosive esophagitis was uncom mon in
both indigenous Fijians and Indians, being detected in only 2% of a
total of 693 endoscopic examinations［16］.
This contrasts with the higher prev alence (11%) of reflux
esophagitis noted by the same author among New Zealanders ［17］.
Esophagitis is likewise uncommon in Japan; a prevalence rate of 3%
was recorded among 240 consecutive outpatients with dyspepsia［18］.
Our own retrospective series from Singapore showed that of 11943
patients undergoin g diagnostic upper endoscopy for various
complaints, 4% had esophagitis［19］.
This frequency was lower than those reported from Western centers［20,21］.
Thus, with the exception of the Taiwanese series, the proportion of
patients with endoscopic esophagitis in Asian series appears lower
than that in reports from Western countries. The severity of
esophagitis also appears mild, unl ike that in Western populations［20,21］.
Prevalence of hiatus hernia
Hiatus hernia, as seen on barium studies, appears rare in
the Far East with a ＜
1% prevalence［22］.
Recent endoscopic series from Asia confirm this impression. Chang et
al from Taiwan found hiatus hernia in 2% of patients endoscoped
as part of an annual medical examination［14］.
In another Taiwanese study in patients endoscoped for
gastrointestinal complaints, hiatus hernia was found in 7% of the
cases［15］.
In our retrospective series from Singapore, the proportion of hiatus
hernia among patients seen for gastrointestinal complaints was 3%［19］.
Thus, the available data show that the prevalence of hiatus hernia
is lower than that in Western series (17%-22%)［20,21］.
Prevalence of GERD complications
The prevalence of Barrett′s
esophagus varies, depending on the population being studied. In a
series from Taiwan, 2% of patients endoscoped for a variety of upper
gastrointestinal symptoms were found to have Barrett′s
esophagus［15］.
When evaluating only those with erosive esophagitis, this rate
increas ed to 14%. The corresponding figures from the West are
4%-20%［23,24］and
36%, respectively［23］.
Reports from a Taiwanese center, and our own center showed a
frequency of benign (presumably reflux-related) esophageal stri
cture of only 0.4% and 0.2% respectively, among patients endoscoped
for variou s gastrointestinal indications［16,19］.
These frequencies are lower in co mparison with those in reports
from the West［25］.
POSSIBLE REASONS FOR THE LOW FREQUENCY OF GERD IN THE EAST
The pathogenesis of reflux esophagitis can be considered in
terms of excessive acid load overwhelming mucosal defense. The
degree of acid load is in turn determined by the anti reflux barrier
of the gastro_esophageal junction［26］
, the quantity of acid refluxed［27］,
and the ability of the esophagus to clear any refluxate back into
the stomach［28］.
The latter depends on the integrity of peristaltic function［29］
and the neutralizing ability of
swallowed saliva［28］.
More recently, an inverse relationship between -H elicobacter pylori
(H. pylori) and GERD has been suggested［30］.
By exa mining the potential pathogenetic factors, it is hoped that
the lower frequency of GERD in the East than in the West could be
explained.
Anti-reflux barrier
An increase in intra-abdominal and intragastric pressure
overcomes the gastroes ophageal pressure gradient maintained by the
lower esophageal sphincter (LES). S uch an increase may occur
through obesity［31］and
delayed gastric emptyi ng by fatty meals［32］.
Alcohol, smoking and fat can lower the LES pressu re and esophageal
peristalsis, thus favoring the occurrence of gastroesophageal reflux［33-35］.
A large hiatus hernia traps gastric contents in its pouch above the
diaphragm. This leads to free retrograde flow of acid into the
esopha gus.
Increased
body mass index and presence of hiatus hernia were found to be the
most important factors associated with the occurrence of esophagitis
in a recent study from Taiwan［14］.
The authors suggested that the lower prevalence of hiatus hernia and
smaller body mass index in the Chinese population might account for
the lower prevalence of reflux esophagitis in Taiwan. The low
prevalence of hiatus hernia in the East has previously been
attributed to the consumption of high residue diets in the
developing world［22］.
Another report from Taiwan found erosive esophagitis to be
associated with smoking, and alcohol consumption［15］.
The authors suggested that the recent increase in smoking, alcohol
use, and fat consumption among Taiwanese were contributed to the
observed rise in the prevalence of GERD in Taiwan.
Gastric acid output
Since acid secretion correlates with body surface area,
Asians in general are ch aracterized by a smaller parietal cell mass
and a lower acid output as compared with Caucasians［36］.
Except for the striking example of Zollinger-Ellis on syndrome,
however, the association between the amount of acid output and the
occurrence or severity of reflux disease has remained unproven［37］.
Acid clearance
While evaluating the consecutive Singaporean patients who
underwent esophageal m anometry, we found that poor esophageal
clearnance was more common among those with esophagitis than among
those without. The results were identical to Western studies［38］.
It is possible that this clearance mechanism has an inherited basis,
and is more efficient in Asians than in Caucasians. Data to support
this is, however, lacking.
Mucosal defence
Presently, there is no risk factor known to disrupt tissue
resistance, except fo r nonsteroidal anti inflammatory drugs［39］.
Such drugs cannot be an imp ortant factor underlying the
geographical variation in the prevalence of GERD, b ecause they are
consumed by Asians no more than by Westerners. However, it is p
ossible that inborn differences in tissue resistance, due to yet
unrecognized fa ctors, may account for some of the geographical
differences.
H. pylori infection
There is circumstantial evidence to suggest that H. pylori
infection is rela tively protective for the occurrence of GERD［30］.
It has been suggested that Hong Kong Chinese are protected against
reflux esophagitis by their high prevalence of H. pylori associated
gastritis［40］.
Such gastritis, whe n beco_ming chronic, can lead to gastric atrophy
and hypochlorhydria, thereb y red ucing the likelihood of GERD. If
this hypothesis is correct, the effects of H. pylori induced
gastritis may be an important factor determining the lower pr
evalence of reflux esophagitis in this part of the world, in which
H. pylori infection is especially common. No data, however, exists
to support this hypot hesis.
Genetic factors
It is unlikely that the lower frequency of GERD in Asian
populations can be expl ained simply by the known extrinsic risk
factors, such as obesity, smo_king habits, and alcohol consumption,
being less frequent in Asians as compared with Caucasians. It is
likely that genetic factors are involved. If that was the case, the
mechanisms through which they confer protection against GERD are
poorly understood. It may be that LES function is truly more
competent in Asians compared with Westerners. Alternatively, the
esophageal mucosa in Asians is inherently more a cid resistant.
Differences in gastric acid output and esophageal clearance ability
between Asian and Western patients are further possibilities.
Comparative studies into these parameters in Eastern and Western
populations may shed more light on this question, and may lead to
formulation of appropriate- therapeutic strategies.
In
summary, most reports from Asia have suggested that GERD is an
uncommon condition in this part of the world. The reasons for the
lower frequency compared with the West are not known, and further
studies are required.
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