DISCUSSION
This study investigated the prevalence of GI symptoms continuously in patients with diabetes for a short period of time at seven hospitals located in Seoul, Incheon, Daejoen, and Gyeonggy (selected to represent the whole country). In total, 608 subjects were included and were composed of 249 (41%) men and 359 (59%) women. Their ages were less than 30, 30-39, 40-49, 50-59, 60-69, and 70 or older in 3.6%, 7.6%, 19.1%, 37.5%, 28.5%, and 3.8% of the subjects, respectively, and the age distribution was similar to that of the national survey on the prevalence of diabetes [
11]. The national survey was conducted with 146,944 Korean adults, and it reported that the prevalence rates of diabetes in males and females were 4.6% and 8.1%, respectively. In this study, the subjects' body mass index (BMI) and HbA1c level were 23.5±3.25 kg/m
2 (men, 22.9±2.93; women, 23.9±3.41) and 8.1±2.1%, respectively, and they did not differ from those of patients with NIDDM in other surveys reported in Korea (22.7-24.6 kg/m
2 and 7.54-9.12%, respectively) [
12,
13]. The BMI of patients with NIDDM in the West and in Hong Kong [
14] were reported to be 28.0-30.3 kg/m
2 and 24.7±4.1 kg/m
2, respectively, and those of Western subjects were higher than those of this study, whereas those of Hong Kong subjects were not different from those found in this study.
The gender, age distribution, and clinical characteristics of the subjects in this study were similar to those in other studies on diabetes prevalence in Korea. Although this study was not a sample survey representing all patients with NIDDM in Korea, its results are considered meaningful because we continuously investigated patients visiting the second or the third hospitals in various regions of the country.
When the results of this study were compared with those of a survey conducted with Koreans in rural areas [
9], the frequencies of reflux, heartburn, dyspepsia, constipation, and other symptoms were not significantly different. This differed from the results of foreign research [
1-
3], which found that patients with diabetes showed more GI symptoms. In this study, women had more GI symptoms, and this result was the same as that in studies reporting that the prevalence rates of GI symptoms were higher in females than males [
6]. Although the frequencies of alcohol consumption and smoking, which can increase these symptoms, were higher in men than in women (
p<0.001), the result that women had more GI symptoms could be explained by the fact that females in the general population show higher rates of GI symptoms [
15].
Among the esophageal disorder prevalence rates, the rates of reflux and heartburn experienced one or more times per week were 4.4% and 7.1%, respectively. The rate of heartburn in this study was considerably lower than that of Western patients with diabetes (25-31.7%) [
7,
16], which was thought to be attributable to the rate of GERD being lower in Asian countries compared to Western countries. The rate of heartburn in the Hong Kong survey (8.1%) was similar to that of this study, and the rates in the Korean population in rural areas were also similar with those of this study (6.9% and 5.2%, respectively). The BMI values of patients with diabetes in this study and in the Hong Kong survey were lower than the BMIs of Western studies. While previous research [
17] revealed that the prevalence of GERD was higher in obese patients, a recent study reported no correlation between obesity and GERD [
18]. Therefore, the effect of the difference in BMI between the continents on the prevalence rates was considered to be low.
The nausea and vomiting prevalence rates among upper GI symptoms were 6.7% and 1.6%, respectively. In a survey performed in Finland [
7] applying the same criteria as this study, the prevalence of nausea was 17% and 18% in males and females, respectively, and that of vomiting was 5% and 6% in males and females, respectively. Although the criteria were not different from those of this study, other research [
2,
19] has reported that the prevalence rates of nausea and vomiting were 16.8-21.0% and 5.6-16.0%, respectively. The Hong Kong survey also found that the prevalence of nausea or vomiting was 3.4%, and that the rate of the diseases among patients with diabetes in Asia was lower than in the West. Compared to a survey conducted in the United States, the lower prevalence of nausea, vomiting, early satiety, and abdominal distention shown in this study was considered to be caused by the decrease in symptoms due to a higher frequency of drug administration, especially prokinetics, in Korean patients (15.2%) compared to that in the U.S. survey (1.5%) [
20]. As the prevalence rates of early satiety and abdominal distention were 32.2% and 21.0%, respectively, in the U.S. sample survey [
2], the U.S. levels were higher than those of this study. The rates in the Hong Kong survey were 6.7% and 21.5%, respectively.
The prevalence of dyspepsia in patients with diabetes in this study was 13.2%, which was lower than that of previous Western research reporting 15.1-28.3% (15.1-15.4% in the U.S. sample survey, 27.1% in a Finnish survey, and 28.3% in a Swedish survey), a Chinese study reporting 16.1%, and a Korean rural population study reporting 15.5%. According to the results of analysis on administered drugs and prescribed drugs, the prevalence of patients taking at least one antacid or prokinetic, except for those patients diagnosed with dyspepsia, was higher at 18.9%, and this higher frequency of medication could have led to the lower dyspepsia prevalence rate. If subjects taking drugs were included, the prevalence of Korean patients with diabetes would be 27.8% (95% CI, 24.2 to 31.4).
Among lower GI symptoms, the prevalence of constipation was 15.0%. The prevalence rates for the U.S. sample survey [
20], the European surveys, and the Hong Kong survey were 10.0%, 13.1-22.1% (22.1% in a German survey [
5], 13.1% in a Swedish survey [
6], and 20.4% in a Finnish survey [
7]), and 27.5%, respectively, indicating that constipation was a very common GI symptom in patients with diabetes. Therefore, the administration of constipation drugs was investigated in most research. Patients with diabetes taking constipation drugs in the U.S. sample survey, the Finnish survey, and the Swedish survey were 15.1%, 7.5%, and 3.4%, respectively, and these frequencies were higher compared to those of the general population in all surveys. In this study, patients taking constipation drugs were found frequently (16.0%), and the level was also higher than that of the general Korean population (10.5%) surveyed by our department [
9]. This difference was considered to follow the higher rate of constipation in patients with diabetes and the higher likelihood of taking a constipation drug. In previous studies on GI symptoms, investigations of the administration of drugs, except constipation drugs, have rarely been conducted. According to research performed in the United States with a sample population in Minnesota [
20], administered drugs could affect GI symptoms. In this research, the frequencies of patients taking constipation drugs, antacids, acid suppression drugs, and prokinetics were 15.9-17.0%, 10.9-12.0%, 5.1-9.2%, and 1.5%, respectively, and those of the nondiabetes control group were 10.0-14.7%, 21.2-23.9%, 7.1-13.8%, and 0.5%, respectively. Although only calcium channel blockers were related to constipation among these administered drugs, acid suppression drugs, prokinetics, or others could induce changes in GI symptoms. Therefore, future studies on GI symptoms should be conducted along with surveys on drug administration. The rate of diarrhea in this study was 11.2%, and those in the U.S. sample survey and European studies were 15.1% and 9.5-13.1% (9.5% in the Finnish survey and 13.1% in the Swedish survey), respectively. Because the rate in the Hong Kong survey was 34.9%, it was different from that of this study. In other words, the prevalence rates of constipation and diarrhea in Hong Kong and Korea were considerably different, although both are Asian countries. This difference was considered to occur because the Hong Kong survey defined constipation and diarrhea subjectively as difficulties during defecation and as increased frequency of defecation along with a loose stool, respectively.
To evaluate the effects of the diabetes morbidity period on the occurrence of GI symptoms, subjects were divided into a 10 year or greater morbidity group and a less than 10 year group, and the prevalence rates for constipation and fecal incontinence were higher in the 10 years or greater morbidity group. The Hong Kong survey [
14] also investigated the correlation between GI symptoms and various diabetes-related factors through multivariate analysis and revealed that only the diabetes morbidity period was an independent variable related to the occurrence of GI symptoms in patients with diabetes.
The prevalence rates of diabetes complications were very different according to the definition and morbidity period, as shown in the results that the rates of diabetic neuropathy were 10-100% in foreign countries and 8.8-78.1% in Korea [
21]. Additionally, whether diabetes complications increased the prevalence rates of GI symptoms was answered differently according to different studies [
5,
14,
16,
19,
22-
24]. While one study reported no correlation between diabetic neuropathy and the occurrence of GI symptoms and neuropathy being more related to mental factors [
19], other studies found that among the diabetes complications, neuropathy was related to the occurrence of GI symptoms [
16,
24]. Although many studies have shown that diabetes complications increase the prevalence of GI symptoms, the results were different according to various factors, such as types of GI symptoms and gender. According to the results of this study, the frequencies of only the administration of constipation drugs and fecal incontinence, among GI symptoms, were higher in the complication group than in the non-complication group. No difference in the frequencies of other GI symptoms was observed according to the existence of a complication, which was similar to that of a current report [
25]. In the Swedish survey, the frequency of heartburn in the complication group was lower than that in the non-complication group, and Channer et al. [
23] showed that the frequencies of upper GI symptoms were higher in patients who had diabetes with anatomic neuropathy compared to the control group. While neuropathy provokes GI symptoms by infiltrating into motor nerves to induce GI dysmotility, if the disease infiltrates into sensory nerves, it could result in serious movement disorders without symptoms. Future studies with more patients are needed to examine the association between neuropathy and GI symptoms in patients with diabetes. Whether the GI symptom prevalence rates increase in an uncontrolled sugar group among such patients has also yet to be decided [
14,
24,
26]. This study found, like other current studies, that sugar control did not affect GI symptom occurrence [
27]. Only the administration of constipation drugs and adjuvant therapies, such as enema, was observed more frequently in patients with diabetes who had uncontrolled sugar levels.
The prevalence of diabetes has continued to increase, and hospitalization, death, and complications following the disease have grown to account for an important part of the Korean public health condition. Nationwide research, including samples of nondiabetic persons, on the clinical patterns and complications of GI symptoms in diabetes as a representative adult Korean disease is desperately needed.