Impact of Obesity on Medical Problems and Quality of Life in Taiwan

American Journal of Epidemiology, Sep 2004

Little is known about the impact of obesity on medical problems and quality of life for people in the Asia-Pacific region. This January 2002–June 2003 cross-sectional study surveyed 6,318 Taiwanese (3,540 men and 2,778 women) visiting health screening centers in southern Taiwan. The authors used the body mass index classification endorsed by the World Health Organization for people in this region. Information was collected on 15 medical problems and quality of life outcomes, measured by the Medical Outcomes Study Short Form 36 questionnaire. After adjustment for age, lifestyle, and sociodemographic factors, and after comparison of subjects with those not overweight or obese (reference group), an increasing trend of body mass index effects based on this reference category was observed on hypertension, hypercholesterolemia, hypertriglyceridemia, type II diabetes, hyperuricemia, pulmonary function impairment, fatty liver disease, and osteoarthritis in both sexes (p < 0.01). Concerning quality of life, an increasing trend of body mass index effects was also observed on the outcomes physical functioning and bodily pain for both sexes and role limitation due to physical problems for women (p < 0.05). Specifically, only the physical functioning domain, including daily activities such as climbing stairs, bending, walking, or some moderate activities, was significantly associated with obesity and was limited to class II obesity.

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Impact of Obesity on Medical Problems and Quality of Life in Taiwan

American Journal of Epidemiology Copyright 2004 by the Johns Hopkins Bloomberg School of Public Health All rights reserved Impact of Obesity on Medical Problems and Quality of Life in Taiwan Wen-Ling Tsai 1 2 Chun-Yuh Yang 0 2 Sheng-Fung Lin 2 4 Fu-Min Fang 2 3 0 Institute of Public Health, Kaohsiung Medical University , Kaohsiung , Taiwan 1 Department of Cosmetic Application and Management, Yung Ta Institute of Technology and Commerce , Pintung , Taiwan 2 Graduate Institute of Medicine, Kaohsiung Medical University , Kaohsiung , Taiwan 3 Department of Radiation Oncology, Kaohsiung Chang Gung Memorial Hospital , Kaohsiung , Taiwan 4 Department of Internal Medicine, Kaohsiung Medical University , Kaohsiung , Taiwan Little is known about the impact of obesity on medical problems and quality of life for people in the Asia-Pacific region. This January 2002-June 2003 cross-sectional study surveyed 6,318 Taiwanese (3,540 men and 2,778 women) visiting health screening centers in southern Taiwan. The authors used the body mass index classification endorsed by the World Health Organization for people in this region. Information was collected on 15 medical problems and quality of life outcomes, measured by the Medical Outcomes Study Short Form 36 questionnaire. After adjustment for age, lifestyle, and sociodemographic factors, and after comparison of subjects with those not overweight or obese (reference group), an increasing trend of body mass index effects based on this reference category was observed on hypertension, hypercholesterolemia, hypertriglyceridemia, type II diabetes, hyperuricemia, pulmonary function impairment, fatty liver disease, and osteoarthritis in both sexes (p < 0.01). Concerning quality of life, an increasing trend of body mass index effects was also observed on the outcomes physical functioning and bodily pain for both sexes and role limitation due to physical problems for women (p < 0.05). Specifically, only the physical functioning domain, including daily activities such as climbing stairs, bending, walking, or some moderate activities, was significantly associated with obesity and was limited to class II obesity. body mass index; cross-sectional studies; gallstones; health; obesity; quality of life Abbreviations: BMI, body mass index; QOL, quality of life; SD, standard deviation; SF-36, Medical Outcomes Study Short Form 36. - Obesity has become a major public health problem of global significance. The prevalence rate of obesity is increasing in all parts of the world, both in affluent, developed countries and in poorer, developing nations. It has been reported that the prevalence rate of obesity in the United States increased 50 percent from 1991 to 1998 (1). According to a national survey in Taiwan conducted from 1992 to 1997, the prevalence rate of obesity was about 25 percent for adult Taiwanese, and mean weight increased 25 kg at all age levels compared with data from a previous 19861988 investigation (2). Obesity has proven to be associated with a variety of chronic diseases such as coronary artery disease, hypertension, type II diabetes, and several cancers and is also considered the second leading avoidable cause of mortality in Western countries (3, 4). In addition, a growing body of literature describes the close association between obesity and quality of life (QOL) (5). In the past decade, QOL has gained increasing interest as an outcome measure in clinical medicine and public health. QOL is based on two fundamental premises. First, it is a multidimensional construct incorporating physical, psychological, social, and emotional functional domains. Second, it is subjective and is reported according to a persons own experiences. Several studies have demonstrated that obese people have a lower QOL, especially regarding the physical aspects of daily life, compared with their normal-weight counterparts (612). Body mass index (BMI; weight (kg)/height (m)2) is one of the most popular anthropometric indices. Different BMI cutoff points describe obesity in different ethnicities. For Caucasians, the definition of obesity according to the international classification endorsed by the World Health Organization is as follows: 25.029.9 kg/m2, overweight; 30.034.9 kg/m2, class I obesity; 35.039.9 kg/m2, class II obesity; and 40 kg/m2, class III obesity (13). For people in the AsiaPacific region, the definition differs: 23.024.9 kg/m2, overweight; 25.029.9 kg/m2, class I obesity; and 30.0 kg/m2, class II obesity (14). Only a small number of studies have investigated the association between obesity and medical problems for people in the Asia-Pacific region. To our knowledge, the impact of obesity on QOL for people in this area has not been explored. In this cross-sectional study, we examined and quantified the impact of obesity, according to the Asia-Pacific BMI classification, on a wide range of medical problems and QOL in a large sample of Taiwanese men and women. MATERIALS AND METHODS Study population The data were collected from people visiting the health screening centers of Chang Gung Memorial Hospital in southern Taiwan for checkups. Monthly, about 400 Taiwanese visited the units for this reason. Subjects whose body weight had changed by more than 5 percent in 3 months were excluded from this study. Among the 6,571 Taiwanese consecutively visiting the units from January 2002 to June 2003, 3,540 men and 2,778 women aged 2079 years were enrolled. Of these subjects, 4,798 (2,846 men and 1,952 women) completed the QOL questionnaire. The items covered in the health checkups included medical history, physical examinations, and a series of laboratory, radiologic, and endoscopic examinations. All examinations were performed and diagnoses confirmed by medical specialists. A wide range of medical problems was surveyed; these problems were chosen on the basis of their known relation to obesity or because they were highly prevalent in Taiwan. Fifteen medical problems were analyzed and were categorized according to the body systems affected. This information is presented in table 1. Definition of medical problems Cardiovascular and metabolic system. Sitting blood pressure was measured by using a standard mercury sphygmomanometer. Systolic (Korotkoff phase 1) and diastolic (Korotkoff phase 5) blood pressures were measured twice on the right upper arm, and the average was used for analysis. Fasting plasma glucose, total cholesterol, triglyceride, and serum uric acid were tested by using a Hitachi 7450 biochemical analyzer (Hitachi Ltd., Tokyo, Japan). Hypertension was defined as a systolic blood pressure of 140 mmHg and/or a diastolic blood pressure of 90 mmHg or current use of antihypertensive drugs. Type II diabetes mellitus was defined as a fasting plasma glucose concentration of 126 mg/dl or current use of antidiabetic agents. Hyperuricemia was defined as a serum uric acid concentration of >8.3 mg/dl or current use of agents to treat gout. The criteria for hypercholesterolemia and hypertriglyceridemia were a total plasma cholesterol concentration of 200 mg/dl and a triglyceride level of >150 mg/dl, respectively. Respiratory system. Spirometry measurements were performed by using a calibrated rolling seal spirometer (Spirotrac 6800; Vitalograph, Inc., Lenexa, Kansas) while subjects were seated. Forced vital capacity and forced expiratory volume in 1 second were measured. A diagnosis of pulmonary function impairment was applied if the predicted forced expiratory volume in 1 second was below 75 percent and/or the predicted forced vital capacity was below 80 percent. Subjects were diagnosed with chronic obstructive pulmonary disease if their clinical presentation or history was compatible with the definitions of asthma, emphysema, or bronchiectasis and the chest radiograph showed typical hyperinflation, chronic bronchial infiltration, and/or peribronchial infiltration. Hepatobiliary and gastrointestinal system. Endoscopic examinations, which included the esophagus, stomach, duodenum, colon, and rectum, were performed by a gastroenterologist. A diagnosis of polyps, hemorrhoids, or ulcers was given from the results of an endoscopic inspection with or without pathologic examination. A diagnosis of chronic viral hepatitis was applied if the serum hepatic function test revealed that the subject was a carrier of hepatitis B and/or C virus and the hepatic sonography showed a coarse liver echotexture, uneven liver contour, and partial obliteration of the hepatic vasculature. A diagnosis of gallstone disease (cholelithiasis) was given if a stone-like radiologic picture and/or a mobile echogenic structure with acoustic shadowing in the gall bladder was found. If the echogram showed increased sound attenuation of the liver parenchyma with impaired visualization of the borders of the hepatic vessels, the subject was diagnosed with fatty liver disease (hepatic steatosis) (15). Musculoskeletal system. A diagnosis of osteoarthritis was given if plain radiographic films revealed joint space narrowing, osteophytosis at articular margins and/or eburnation of subchondral bone in the knee or hip joint, or apparent marginal osteophytes and/or interspace narrowing of the lumbar spinal bones (16). Measures of BMI Trained research staff measured height by using a stadiometer and weight with a calibrated digital scale for participants who were wearing a clinic gown. BMI was calculated by dividing weight in kilograms by the square of height in meters. Measures of QOL The Medical Outcomes Study Short Form 36 (SF-36) questionnaire (Taiwan Chinese version) was used to measure QOL (17). This self-administered questionnaire includes 36 items, in a Likert-type or forced-choice format, and contains brief indices of the following eight functional domains: 1) physical functioning (10 items, 3-point scale), 2) role limitation due to physical problems (role physical; four items, 3-point scale), 3) role limitation due to emotional problems (role emotional; three items, 2-point scale), 4) social functioning (two items, 5-point scale), 5) bodily pain (two items Body mass index 25.029.9 (39.1%) Women (n = 2,778) 23.024.9 25.029.9 (22.1%) (23.8%) 48.6 (13.0) 47.5 (14.6) 49.1 (12.7) 50.0 (11.5) 43.1 (13.7) 47.9 (13.3) 42.4 (12.8) 51.3 (11.4) 54.0 (11.6) 53.8 (13.1) each, 5- and 6-point scales), 6) vitality (four items, 6-point scale), 7) mental health (five items, 6-point scale), and 8) general health perception (five items, 5-point scale). Health change in the past year (one item, 5-point scale) was also assessed. Scores for each domain ranged from 0 to 100, with high scores indicating a better status (18, 19). The Taiwan Chinese SF-36 has been used by other researchers and has been shown to have good construct validity and high internal reliability (20, 21). Measures of potential confounders All sociodemographic data (age, gender, number of years of education, annual family income, employment, and marital status) and lifestyle variables (smoking, alcohol consumption, and exercise frequency) were obtained by using a self-administered questionnaire. Alcohol consumption and smoking status were assessed by using a 3-point scale (e.g., no history of smoking, past smoking, current smoking). Frequency of exercise was assessed with the following question: How many times do you exercise every week? Statistical analysis Scores for the eight functional domains of the Taiwan Chinese SF-36 were calculated according to the SF-36 manual (18). Logistic regression analysis (SPSS for Windows, version 10.0; SPSS, Inc., Chicago, Illinois) was used to determine odds ratios and associated 95 percent confidence intervals. Each of the diagnosed medical problems or poor QOL ratings was used as a dependent variable in separate regression models. The distributions of the scores for the eight functional domains were examined to identify the cutoff values for good and poor QOL. Subjects whose score was less than 66.7 percent were assessed as having a poor QOL, and those scoring 66.7 percent or above were considered to have a good QOL. The items for each functional domain were also dichotomized so that above-average scores for items with an odd-numbered scale (3 or 5 points) indicated a good QOL and scores that were average or lower indicated a poor QOL. For items with an even scale (2, 4, or 6 points), the scores for good and poor QOL were divided evenly. Dummy variables for BMI (independent variable) were created by using BMI <23.0 kg/m2 as the reference. For medical problems, adjustments were made for age, sociodemographic factors (number of years of education, annual family income, marital status, and employment), and lifestyle (smoking, alcohol consumption, and exercise frequency). For the QOL analysis, additional adjustments were made for the diagnosed medical problems found to be significantly correlated with BMI. Statistical significance of trends was calculated by categorizing exposure variables and treating scored variables as continuous in logistic regression analysis. Men and women were analyzed separately because of expected differences between the sexes in both the dependent and independent variables. Subject characteristics For men (n = 3,540) and women (n = 2,778), respectively, mean age was 48.6 (standard deviation (SD), 13.0) years and 47.9 (SD, 13.3) years, weight was 70.1 (SD, 15.8) kg and 58.3 (SD, 9.9) kg, height was 168.0 (SD, 24.5) cm and 156.2 (SD, 5.5) cm, and BMI was 24.9 (SD, 3.5) kg/m2 and 24.0 (SD, 4.0) kg/m2 (table 1). Twenty-six percent of the men were overweight, 39.1 percent had class I obesity, and 5.7 percent had class II obesity. Among the women, 22.1 percent were overweight, 23.8 percent had class I obesity, and 6.3 percent had class II obesity. Obese men were more likely to be employed and to have a higher annual family income; in contrast, obese women were more likely to be unemployed and to have a lower annual family income. Obese women tended to have lower educational attainment. On the other hand, educational attainment did not differ significantly across BMI categories for men. With regard to lifestyle, the prevalence rate of current smoking was 53.4 percent for men and 5.7 percent for women. For both men (61.1 percent) and women (9.8 percent), current smoking was seen more often in the class II obesity group. The mean frequency of exercise per week was 1.7 (SD, 1.3) times for men and 1.6 (SD, 1.4) times for women. Exercise frequency was inversely associated with BMI for men, but a clear pattern was not found for women. Medical problems Cardiovascular and metabolic system. The mean value of systolic blood pressure was 131 (SD, 17) mmHg in men and 128 (SD, 20) mmHg in women. The respective concentrations of plasma total cholesterol, triglyceride, fasting glucose, and uric acid were 199 (SD, 63) mg/dl, 147 (SD, 130) mg/dl, 112 (SD, 55) mg/dl, and 7 (SD, 13) mg/dl in men and 199 (SD, 64) mg/dl, 116 (SD, 83) mg/dl, 107 (SD, 33) mg/dl, and 7 (SD, 13) mg/dl in women. The prevalence of hypertension, hypertriglyceridemia, type II diabetes, and hyperuricemia was higher in men than in women (p < 0.05). After adjustment for age, lifestyle, and sociodemographic factors, and comparison of subjects with those not overweight or obese (reference group), an increasing trend of BMI effects based on this category was observed for all four medical variables for both sexes (p < 0.01) (table 2). Consistency of the BMI effects was generally observed for most of these variables as a group after we examined the 95 percent confidence intervals within each BMI level. For men, statistically significant odds ratios for hypercholesterolemia, hypertriglyceridemia, and hyperuricemia were found for those in the overweight, class I, or class II obesity group and for hypertension and type II diabetes in the class I or class II obesity group. For women, statistically significant odds ratios for hypertension, hypercholesterolemia, hypertriglyceridemia, and type II diabetes were found for those in the overweight, class I, or class II obesity group and for hyperuricemia in the class I or class II obesity group. Respiratory system. The mean values of forced vital capacity and forced expiratory volume in 1 second were 89.4 (SD, 15.9) percent and 85.2 (SD, 14.6) percent in men and OR 95% CI Body mass index Medical problems Cardiovascular and metabolic system Hypertension 1.2 Hypercholesterolemia (200 mg/dl) 1.2 Hypertriglyceridemia (>150 mg/dl) 1.8 Type II diabetes (fasting glucose 126 mg/dl) 1.2 Hyperuricemia (>8.3 mg/dl) 1.8 Respiratory system Impaired pulmonary function 1.1 Chronic obstructive pulmonary disease 0.7 Asthma 0.7 Hepatobiliary and gastrointestinal system Gallstones 1.1 Fatty liver disease 2.0 Chronic viral hepatitis 1.0 Hemorrhoids 1.1 Peptic ulcer 1.0 Polyps 0.9 Musculoskeletal system Osteoarthritis 1.2 Quality of life (poor) Physical functioning 1.1 Role physical# 0.9 Role emotional** 1.0 Social functioning 0.9 Bodily pain 1.0 Vitality 0.9 Mental health 0.9 General health 0.9 2.1 1.6, 2.6 1.6 1.3, 1.9 2.9 2.4, 3.7 1.3 1.1, 1.5 2.3 1.7, 3.1 4.2, 10.3 <0.001 1.4 0.9, 1.9 1.5 1.1, 1.9 89.5 (SD, 17.2) percent and 86.7 (SD, 15.2) percent in women, respectively. An increasing trend of BMI effects was observed on pulmonary function impairment for both sexes (p < 0.01). A statistically significant odds ratio was found only for those of both sexes with class II obesity. In contrast, for both sexes, the trend of BMI effects on chronic obstructive pulmonary disease or asthma was not significant. Hepatobiliary and gastrointestinal system. Of the six medical variables (gallstones, fatty liver disease, chronic viral hepatitis, hemorrhoids, peptic ulcer, and gastrointes Body mass index Men (n = 2,846) Women (n = 1,952) 23.024.9 25.029.9 (26.0%) (39.1%) 23.024.9 25.029.9 (22.1%) (23.8%) Physical functioning Role physical Role emotional Social functioning Bodily pain Mental health General health tinal polyps), an increasing trend of BMI effects was observed for only fatty liver disease for both sexes (p < 0.01). Conversely, the BMI effects were found to be consistent but statistically insignificant regarding the other five variables. For fatty liver disease, the odds ratio was significant for those in the overweight, class I, or class II obesity group for both sexes. It was as much as 20 times higher in the class II obesity group (table 2). Musculoskeletal system. The prevalence rate of osteoarthritis was 41.2 percent for men and 41.4 percent for women. An increasing trend of BMI effects was observed on osteoarthritis for both sexes (p < 0.01). The odds ratio was significant for men who had class I or II obesity and for women in the overweight, class I, or class II obesity group. Table 3 shows the unadjusted prevalence of poor QOL for the eight functional domains of the SF-36. After adjustment for age, lifestyle, sociodemographic factors, and medical problems, a statistically significant (p < 0.05), increasing trend of BMI effects was found on physical functioning and bodily pain for both sexes and for role physical for women. The only statistically significant odds ratio was the one corresponding to physical functioning for those subjects with class II obesity (men: odds ratio = 3.2, 95 percent confidence interval: 2.1, 5.1; women: odds ratio = 2.7, 95 percent confidence interval: 1.7, 4.5) (table 2). Otherwise, the individual items of the physical functioning domain are presented in table 4. Odds ratios were statistically significant for moderate activities, bending, walking, and climbing several stairs for both sexes; and for lifting or carrying groceries, climbing one flight of stairs, and self-bathing or dressing for women. DISCUSSION Taiwan is located in the center of the East-Asian island arc and has a population of 22 million. Most of the islands inhabitants are the descendants of immigrants from Mainland China. With an improving economy and changing habits influenced by Western diets, obesity is becoming a threatening health problem for people on this island. Recently, a national nutritional survey revealed that 24.5 percent of the male and 25.2 percent of the female adults in Taiwan were obese, and this prevalence was particularly high (men: 36.6 percent; women: 44.6 percent) among those aged 4564 years (2). Most studies examining the risk of medical problems associated with obesity are based on data from Caucasians in Europe or the United States. It has been shown that for the same body fat level, age, and gender, Chinese BMI is 1.9 kg/ m2 lower than that of Caucasians (22). The increased risks of medical problems associated with obesity are found to occur at a lower BMI in Asians compared with Caucasians (23, 24). However, the optimal cutoff points for BMI to define overweight Asian persons or obesity are still controversial. A cutoff point of 24.2 for overweight individuals and 26.4 for obesity was suggested in Taiwan (2). When predictive values for some cardiovascular risk factors are tested in Mainland China, the recommended optimal cutoff points for BMI are 24.0 for overweight and 28.0 for obese individuals (25). In 2000, the World Health Organization redefined the BMI cutoff points as 23.0/25.0 for overweight/obese individuals in the Asia-Pacific region (14). So far, data on disease association with obesity using this classification endorsed by the World Health Organization are still sparse in the literature, and most studies have focused solely on cardiovascular disease. Ours carried out a more comprehensive survey of medical problems and of QOL among overweight and obese individuals defined by this classification. Climbing several flights of stairs Climbing one flight of stairs 0.8 Walking >1 km Walking 500 m Walking 100 m Self-bathing or dressing Men (n = 2,846) 0.8, 1.2 0.9, 1.4 0.7, 1.3 1.3, 2.1 0.8, 1.5 0.9, 1.8 0.7, 1.2 0.9, 1.6 0.6, 1.5 0.5, 1.3 Body mass index Women (n = 1,952) According to the World Health Organization, medical problems greatly or moderately associated with obesity include type II diabetes, insulin resistance, gallstone disease, dyslipidemia, breathlessness, sleep apnea, coronary heart disease, hypertension, osteoarthritis, and hyperuricemia (26). In addition, there are some less-well-known complications of obesity such as fatty liver disease, pulmonary function impairment, endocrine abnormalities, and obstetric complications (27). Surveying all of these probable complications of obesity was not possible in this cross-sectional study because our data were limited to those that could be investigated by the routine procedures of health screening. Among the 15 medical problems we investigated, an increasing and significant trend of BMI effects based on this category was observed on hypertension, hypercholesterolemia, hypertriglyceridemia, type II diabetes, hyperuricemia, pulmonary function impairment, fatty liver disease, and osteoarthritis for both sexes. Except for gallstone disease, these results are generally compatible with the recognized medical problems associated with obesity in Caucasians. There are mainly two types of gallstones: cholesterol and pigment stones. Gallstones found in Caucasians are most commonly the cholesterol type, which are associated with obesity. In contrast, gallstones found in Oriental people are mainly the pigment type, which are usually associated with chronic hemolytic states and bacterial infections rather than obesity (28, 29). Even though these two types of stones were not distinguishable in the echogram, we speculate that the higher prevalence of pigment stones in our study population might explain the lack of association with obesity. A study of 2,228 Japanese men aged 4955 years receiving a retirement health examination, including an ultrasound scan, also failed to find an association between obesity and gallstone disease (30). Several recent studies have demonstrated a positive association between obesity and asthma, although their causeeffect relations remain to be determined (31, 32). For our subjects, we failed to demonstrate the BMI effect on chronic obstructive pulmonary disease or asthma. However, a crosssectional survey from Mainland China revealed that both extremes of the BMI distribution (underweight and obesity) were significantly associated with symptomatic asthma in men and women (33). A longitudinal survey with more uniform criteria for the disease is needed before an association between obesity and asthma for Asian people can be concluded. The patterns of some medical problems were different between men and women; for example, men had a higher prevalence of hypertension, hypertriglyceridemia, type II diabetes, and hyperuricemia. However, the gender difference in the association of medical problems with BMI was not as remarkable in our sample because it was found in another study (34). Potential age differences were also examined by stratifying into three groups (2039, 4059, and 6079 years). The medical problems associated with BMI were generally similar across the three age strata, despite the statistical inconsistency and instability of some of the medical problems in the age group 6079 years due to the relatively smaller sample size (data not shown). In addition to medical problems, reports show that obesity is also an independent factor affecting QOL. The SF-36 is the most widely used instrument for assessing QOL in the context of obesity. Most researchers who used the SF-36 to survey the general population found that obesity was mainly associated with the physical rather than the mental aspects of QOL. In Caucasian samples, increased body weight was associated with lower physical functioning, role physical, vitality, bodily pain, and general health scores (612). To our knowledge, our study is the first to explore the association between obesity and QOL in non-Caucasians. For our subjects, a significant trend of BMI effects was also observed on physical functioning and bodily pain for both sexes and for role physical for women. Specifically, only the physical functioning domain, including daily activities such as climbing stairs, bending, walking, or some moderate activities, was significantly associated with obesity and was limited to subjects with class II obesity. Except for some individual items in the physical functioning domain, differences in gender or age were not as remarkable as they were in other studies (7, 8, 11). A national survey of the general population is needed to determine whether racial or cultural differences play a role in the impact of obesity on QOL. The response rate for the Taiwan Chinese SF-36 was 76 percent for our subjects. The sociodemographic variables were compared between those who did and did not respond, but no selection bias was detected. Illiteracy was the main reason for nonresponse, indicating a need to provide assistance with reading the questionnaire in an understandable dialect for participants not familiar with the Chinese characters. The limitations of this study deserve comment. First, the analyses were based on cross-sectional data and were limited to those who requested a health checkup. Selection bias may have existed, although we adjusted for many potential confounders. Some medical problems may develop slowly and will not be detected unless a persistent prospective survey or more accurate instrumentation is developed. We cannot rule out the possibility of reverse causality between the medical problem or QOL and obesity (i.e., decreased QOL might lead to obesity) in this cross-sectional survey. Second, we did not use linear regression analysis to determine the relations between the QOL scores and obesity indices because the scores were not distributed normally (data not shown). Therefore, we used logistic regression analysis and introduced cutoff points to define good and poor QOL for the eight functional domains of the SF-36. There are no definite cutoff points for these functional domains to define good and poor. The choice of 66.7 percent as the cutoff point for our subjects was partly arbitrary and partly based on the values used in related reports (7, 34). Third, we did not use other anthropometric indices to detect regional obesity. BMI is an overall index of obesity. Therefore, we may have missed some medical problems or functional domains that tend to be associated with central obesity rather than general obesity. In conclusion, on the basis of this cross-sectional study using the convenience sample, we observed an increasing and significant trend of BMI effects on some medical problems and QOL for people in Taiwan. This result indicates that overweight or obese Taiwanese people are at increased risk of developing a medical problem such as hypertension, hypercholesterolemia, hypertriglyceridemia, type II diabetes, hyperuricemia, pulmonary function impairment, fatty liver disease, or osteoarthritis. In addition, severely obese Taiwanese are prone to have poorer physical functioning, especially regarding daily physical activities. This project was supported by grant NSC91-2320-B182A-010 from the National Science Council of Taiwan. 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Wen-Ling Tsai, Chun-Yuh Yang, Sheng-Fung Lin, Fu-Min Fang. Impact of Obesity on Medical Problems and Quality of Life in Taiwan, American Journal of Epidemiology, 2004, 557-565, DOI: 10.1093/aje/kwh251