Burden of disease attributable to obesity and overweight in Korea

International Journal of Obesity (2006) 30, 1661–1669 & 2006 Nature Publishing Group All rights reserved 0307-0565/06 $30.00 www.nature.com/ijo ORIGI...
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International Journal of Obesity (2006) 30, 1661–1669 & 2006 Nature Publishing Group All rights reserved 0307-0565/06 $30.00 www.nature.com/ijo

ORIGINAL ARTICLE Burden of disease attributable to obesity and overweight in Korea J-H Park1, S-J Yoon2, H Lee3, H-S Jo4, S-I Lee5, Y Kim1, Y-I Kim1 and Y Shin1 1

Department of Health Policy and Management, College of Medicine, Seoul National University, Chongro-ku, Seoul, Korea; Department of Preventive Medicine, College of Medicine, Korea University, Anam-dong Sungbuk-ku, Seoul, Korea; 3Division of Cancer Control and Epidemiology, National Cancer Center, Goyang city, Gyeonggi-province, Korea; 4Department of Preventive Medicine, College of Medicine, Kangwon National University, Hyoja-dong, Chuncheon City, Korea and 5 Department of Preventive Medicine, College of Medicine, University of Ulsan, Pungnap-dong Songpa-ku, Seoul, Korea 2

Objective: To estimate the burden of disease attributable to overweight and obesity using disability-adjusted life-year (DALY) in Korea. Research methods: Firstly, overweight and obesity-related diseases and their relative risk (RR) were selected by the systematic review. Secondly, population-attributable fractions (PAFs) were computed by using the formula including RR and the prevalence of exposure (Pe) of overweight and obesity. Thirdly, DALYs of overweight and obesity-related diseases in Korea were estimated. Finally, the attributable burden (AB) of diseases due to overweight and obesity was calculated as the sum of the products from multiplying DALYs of overweight and obesity-related diseases by their PAFs. Results: The disease burden attributable to overweight was 827.1 person years (PYs) overall, 732.6 for men, 922.9 for women per 100 000 persons. The disease burden attributable to obesity was 260.0 PYs overall, 144.2 for men, 377.3 for women. Diabetes attributable to overweight and obesity accounts for highest burden among other diseases in both genders. The disease burden attributable to overweight was 3.2 times higher than that attributable to obesity. Conclusion: Most proportion of disease burden attributable to high body mass index (BMI) occurred among those with only moderately raised levels such as overweight, not the extremes such as obesity. It suggests that population-based, public health intervention rather than high-risk group-focused strategies are more effective to reduce the burden of disease attributable to overweight and obesity in Korea. International Journal of Obesity (2006) 30, 1661–1669. doi:10.1038/sj.ijo.0803321; published online 14 March 2006 Keywords: overweight; risk factor; disability adjusted life year (DALY); Korea

Introduction Overweight and obesity pose a major risk factor for cardiovascular diseases, stroke, diabetes, hypertension, hyperlipidemia, musculoskeletal diseases and cancer and they are serious public health threats.1,2 The increased prevalence of overweight adds a socioeconomic burden to the public health system. In Korea, obesity-related medical expenses accounted for 0.91–1.88% of total national health expenditures in 1998, and this socioeconomic burden is likely to increase in the future.3 The socioeconomic burden associated with overweight and obesity is higher in developed

Correspondence: Dr S-J Yoon, Department of Preventive Medicine, College of Medicine, Korea University, Seoul, Korea. E-mail: [email protected] Received 21 September 2005; revised 14 February 2006; accepted 16 February 2006; published online 14 March 2006

countries, accounting for 2–7% of total national health expenditures.4 World Health Organization (WHO) predicted in a 1997 report reflecting the opinions of health care experts from 25 nations that obesity will emerge as a great health risk like smoking in the 21st century, although until now it has been largely ignored as a public health concern despite its effect on many health care problems. In Korea, the incidence of overweight increased to 29.6% in 2001 from 24.3% in 1998 among the male population and to 25.9 from 23.5% among the female population during the same period. The incidence of obesity increased to 3.96% in 2001 from 1.7% in 1998 among the male population and to 3.4 from 3.0% among the female population during the same period.5,6 The burden of disease attributable to overweight and obesity is expected to be a significant public health concern in coming years. The burden of disease resulted from the exposure to obesity can be prevented through public health policy. For

Burden of obesity and overweight in Korea J-H Park et al

1662 this reason, WHO introduced DALY in its 2002 report as the unit used for measuring the Global Burden of Disease attributable to 26 risk factors, including obesity.7,8 But WHO report presents burden of disease attributable to obesity only by six subregions, not by specific countries such as Korea. Furthermore, the report provides discussion of uncertainties in estimates of disease incidence, duration, and disability weighting. Uncertainty in this risk assessment is by far dominated by absence or limitations of direct studies on exposure, hazard, and background disease burden. Extrapolation of hazard from limited number of studies to other population which was used in WHO report is another source of potential error.9 Therefore, with the increasing public health impact of obesity, accurate measurement of the burden of disease attributable to overweight and obesity is an essential step in establishing public health interventions designed to prevent obesity-induced diseases in Korea. With above background. This study aimed to estimate the burden of disease attributable to overweight and obesity by gender and age using DALY in Korea and to provide a basis for developing public health strategies needed for the prevention of overweight and obesity. To quantify the burden of diseases, investigators mainly use the disability-adjusted life-year (DALY), developed by researchers in the World Health Organization (WHO). Disability-adjusted life-year is the sum of the life years lost due to disability and premature death. Disability-adjusted life-year-based estimation of disease burden is useful for measuring the health state of a population and comparing health level and public health systems between countries, setting national priorities in the allocation of limited medical care resources and evaluating cost-effectiveness of public health interventions.7

Methods Disease selection related to overweight and obesity To define overweight and obesity, this study used the categories set by WHO: a body mass index (BMI) between 25 and 29.9 kg/m2 was defined as overweight and a BMI of 30 kg/m2 or above as obesity.10 Overweight- and obesity-related diseases were selected through a systematic review using MEDLINE, the Korean National Assembly library and the Research Information Center for Health to screen studies with the following key words: obesity, body weight, over weight, fat, adiposity and BMI. In addition, a hand search was conducted by referring to the citations identified through the recent reviews of obesity-induced diseases.11–16 The selection criteria applied for the selection of research evidence were as follows; firstly, it was published between 1970 and 2004. Secondly, it suggested obesity-induced diseases. Thirdly, it suggested relative risk (RR) values of obesity-induced diseases. Fourthly, it used BMI to define International Journal of Obesity

obesity. Fifthly, it met the 2b level of evidence in the Oxford Center for Evidence Based Medicine Levels of Evidence17 (a cohort study and a systematic review using cohort). We used the research results of the American Institute for Cancer Research (AICR) (1997) to identify obesity-induced cancers.18 The AICR study classified the association between the incidence of cancer and overweight or obesity into the following four categories based on systematic reviews and the opinions of investigators: convincing, probable, possible and insufficient. The study further stressed that the impact of overweight and obesity on those captured under the latter two categories was not clear due to a lack of evidence or divided opinions among investigators. The study included research evidence related to endometrial, breast and Renal cancers as these cancers are captured under the ‘convincing’ and ‘probable’ categories. Finally, recent studies have shown that Asian populations have higher risks of metabolic syndromes such as type 2 diabetes, cardiovascular disease than Caucasians.19–25 Therefore, for diabetes, ischemic heart disease, stroke, we selected studies performed in Asian population.26–28 Especially, for diabetes, ischemic heart disease, we selected studies performed in Korean population.26,28 For stroke, we selected studies performed in Chinese population27 because we could not find such study that suggests RR values of obesity-induced stroke for Korean population yet. A total of 63 studies met the selection criteria and identified 14 diseases related to overweight and obesity (Table 1).26–38

Relative risk assessment The study used the RR ratio suggested in the studies with the highest possible degree of internal and external validity for each of the 14 diseases-related overweight and obesity. Two of the authors separately assessed the internal validity of cohort studies that met the selection criteria using the Newcastle-Ottawa Quality Assessment scales for cohort and case–control studies.39 This assessment instrument is designed to determine the internal and external validity of cohort studies by assessing the representative of the study population, control group, accuracy in measuring exposure to risk factors, explanation for predicted study results, control of major conflicting variables, accuracy in analyzing results, appropriateness of follow-up period, and number of subjects who withdrew from the study. Each item was rated from 0 to 9. The validity of this assessment instrument was proven in earlier studies.39 The study first selected research evidence that had the highest score and in the case of two research evidences having the same score, the one that included research subjects of both genders and a broader range of age groups was selected. The RR ratio and Newcastle-Ottawa Quality Assessment scales of selected study are presented in Table 1. The RR ratio suggested in selected literature was used for the calculation of the burden of disease.

Burden of obesity and overweight in Korea J-H Park et al

1663 Table 1

Overweight and obesity related diseases and its relative risks (RRs)

Disease [NO scalea]

ICD-10

26

Females 2.39 (BMI 25–25.9) 2.61 (BMI 26–26.9) 3.26 (BMI 27–27.9) 3.29 (BMI 28–28.9) 3.54 (BMI 29–29.9) 4.37 (BMIX30) 1.061 (BMI per 2-unit difference) 1.34 (BMIX27.8)

Stroke (Zhow BF et al., 2002)27b

I60–I69

Congestive heart failure (Jiang et al., 2001)28 [9]

I50.0

1.23 (BMIX27.8)

Diabetes mellitus (Oh SW et al., 2004)29 [8]

E10-E14

2.74 (BMI 25o27) 3.65 (BMI 27o29) 4.31 (BMI 29o30) 4.79 (BMI 30o32) 6.75 (BMI 32o34) 7.98 (BMIX34) 1.0 (BMI per 5-unit difference)

Osteoarthritis (Felson et al., 1997)30 [8] Endometrial cancer (Furberg et al., 2003)

I20–I25

Males 2.39 (BMI 25–25.9) 2.61 (BMI 26–26.9) 3.26 (BMI 27–27.9) 3.29 (BMI 28–28.9) 3.54 (BMI 29–29.9) 4.37 (BMIX30) 1.061 (BMI per 2-unit difference)

Ischemic heart disease (Jee SH et al., 2005)

[9]

Relative risks

M15-M19 31

[9]

C54–55

Breast cancer (Brandt et al., 2000)32 [7]

C50

Renal cancer (Marshall, 2002)33b

C64

Pre-eclampsia (O’Brien et al., 2003)34b

O10-O14

Maternal hemorrhage (Cedertren et al., 2004)35 [8]

O44-O46,O67,O72

Obstructed labor (Cedertren et al., 2004)35 [8]

O64-O66

Birth asphyxia and birth trauma (Cedertren et al., 2004)35 [8]

P03,P10-P15,P20-P29

Cholecystitis (Kato et al., 1992)36 [8]

K80-K81

(BMI 25o30) (BMI 30o35) (35–o40) (BMIX40)

1.4 (BMI 23.8-25.8) 1.8 (BMIX25.8)

(Layde et al., 1982)37 [8] Cataract (Weintraub, 2002)38 [7]

1.35 1.70 2.05 2.40

H25-H26

1.07 (BMI 25-27.7) 1.20 (BMIX27.8)

5.08 (BMI 25-o27) 10.77 (BMI 27-o29) 11.19 (BMI 29-o30) 13.15 (BMIX30) 1.8 (BMI per 5-unit difference) Age o50 years: 1.90 (BMI 25–30) 2.59 (BMIX30) AgeX50 years: 2.28 (BMIX30) Postmenopausal(Age o 50 years): 1.14(BMI 21o23) 1.15(BMI 23o25) 1.26(BMI 25o27) 1.43(BMI 27o29) 1.21(BMI 29o31) 1.29(BMI 31o33) 1.27(BMIX33) 1.35 (BMI 25o30) 1.70 (BMI 30o35) 2.05 (35o40), 2.40 (BMIX40) Reproductive age(Age 15–50 years): 1.54 (BMI 25o30), 1.81 (BMI 30o35), 2.08 (35o40), 2.35 (BMIX40) Reproductive age(Age 15 - 50 years): 1.19 (BMI 30o35) 1.35 (35o40) 1.70 (BMIX40) Reproductive age(Age 15 - 50 years): 2.14 (BMI 30o35) 2.82 (35o40) 3.14 (BMIX40) Reproductive age(Age 15–50 years): 1.61 (BMI 30o35) 2.13 (35o40) 2.52 (BMIX40) 1.36 (BMI 22.5o25) 1.74 (BMI 25.0o27.5) 3.26 (27.5o30) 5.54 (BMIX30) 1.07 (BMI 25o27.8) 1.20 (BMIX27.8)

a NO scale: Newcastle-Ottawa quality assessment scale. bType of study is meta analysis using cohort studies. Therefore, we did not measure Newcastle-Ottawa Quality Assessment scales.

International Journal of Obesity

Burden of obesity and overweight in Korea J-H Park et al

1664 The burden of disease attributable to overweight and obesity The following processes was performed to estimate the burden of disease attributable to overweight and obesity: First, the population-attributable fraction (PAF) was calculated using the prevalence of overweight and obesity in the population (pe) and the RR described in the previous paragraph using formulas 1 and 2. Population was calculated using the data of the 2001 National Health and Nutrition Survey of Korea. Formula 1 was used for estimating the attributable burden (AB) of a risk factor while formula 2 was used for estimating PAF (all) of the incidence or mortality attributable to joint effects of multiple risk factors.38,40 For instance, if there are three RR ratios at exposure level, k is 3 in formula 2. At the first exposure level (i ¼ 1), the values of Pe1 and RR1 can be applied. PAF ¼

PeðRR  1Þ PeðRR  1Þ þ 1

PAFðallÞ ¼ 1 

1 k P

ð1Þ

ð2Þ

PeiRRi

i¼1

Secondly, DALY was calculated for each disease by adding the years of life lost due to premature mortality (YLL) and the years lived with disability (YLD). Data used for the calculation of DALY was derived using the 2001 life table of the National Statistical Office (NSO) for calculating life expectancy at birth and NSO’ s 2001 statistics of the cause of death and age at the time of death. The incidence rate of diseases needed for the YLD calculation came from insurance claim data submitted to the National Health Insurance Corporation during the period from 1998 to 2001. The average age at disease onset and the morbidity period were calculated using the DISMOD II model. This study also used the same assumptions adopted by Global Burden of Disease researchers.7 However, we newly developed Korean disability weights for 123 diseases using the person trade-off method in 2003 and used to reflect accurate condition of Korean patient.41 Thirdly, WHO has suggested three methods for measuring the burden of disease attributable to a risk factor such as overweight and obesity: The burden of disease and injury attributable to the risk factor (AB), the overall burden of disease (burden: B) and PAF, a contribution of a risk factor to the proportion of disease and injury attributable to the risk factor in a population (formula 3). AB ¼ BPAF

ð3Þ

AB was calculated for each disease and injury category by multiplying the disease burden by PAF. The burden of disease attributable to the risk factor equals the sum of all attributable disease burdens. AB of overweight and obesity was calculated for each disease category by multiplying its DALY by PAF, and the disease burden attributable to overweight and obesity was calculated by summing up all ABs. International Journal of Obesity

Results Disease burdens attributable to overweight and obesity by gender The disease burdens attributable to overweight and obesity by gender are presented in Table 2. The burden of disease attributable to overweight was 827.1 PYs per 100 000 persons. In terms of the size of overweight-AB, diabetes had the most significant overweight-attributable disease burden overall (535.8 PYs, 64.8%) and for men (435.2 PYs, 59.4%) women (637.8 PYs, 69.1%), followed by ischemic heart disease (205.1 PYs, 24.8%), stroke (50.6 PYs, 6.1%), cholecystitis (20.9 PYs, 2.5%), osteoarthritis (6.8 PYs, 0.8%) and breast cancer (4.0 PYs, 0.5%). The burden of disease attributable to obesity was 260.0 PYs per 100 000 persons. Of the top six categories of diseases in terms of the size of obesity-AB, diabetes had the most significant obesity-attributable disease burden overall 193.7 PYs (74.5%) and for men (91.3 PYs, 63.3%) women (297.6 PYs, 78.9%), followed by ischemic heart disease (46.9 PYs, 18.0%), stroke (9.0 PYs, 3.5%), cholecystitis (8.3 PYs, 3.2%), endometrial cancer (0.5 PYs, 0.2%) and osteoarthritis (0.5, 0.2%).

Disease burdens attributable to overweight by age The burden of overweight-related disease by gender and age is presented in Table 3. In both gender, the overweight-AB reached its highest level in 60s age groups. In both gender, the burden of diabetes attributable to overweight was highest among other diseases in all age groups. The overweight-AB was correlated with age in both men and women for diabetes, ischemic heart disease, stroke,

Table 2 Attributable burden of diseases due to overweight and obesity in Korean (unit: person years/100 000 persons) Disease

Overweight Person Male Female Person

Obesity Male Female

Diabetes mellitus 535.8 435.2 637.8 193.7 91.3 297.6 Ischemic heart disease 205.1 224.2 185.7 46.9 40.0 53.9 Stroke 50.6 47.0 54.3 9.0 6.0 12.0 Cholecystitis 20.9 17.9 24.0 8.3 5.7 10.9 Osteoarthritis 6.8 5.5 8.2 0.5 0.8 0.2 Breast cancer 4.0 0.0 8.0 0.4 0.0 0.8 Renal cancer 1.8 2.4 1.2 0.3 0.4 0.3 Endometrial cancer 1.3 0.0 2.5 0.5 0.0 1.1 Cataracts 0.5 0.3 0.8 0.2 0.1 0.3 Congestive heart failure 0.2 0.1 0.2 0.05 0.02 0.1 Pre-eclampsia 0.1 0.0 0.1 0.01 0.0 0.02 Maternal hemorrhage 0.02 0.0 0.03 0.02 0.0 0.03 Obstructed labour 0.01 0.0 0.02 0.01 0.0 0.02 Birth asphyxia and birth trauma 0.00 0.0 0.0 0.0 0.0 0.0 Total

827.1 732.6 922.9 260.0 144.2 337.3

Overweight: BMI 25–29.9 kg/m2 Obesity: BMI X30 kg/m2.

Burden of obesity and overweight in Korea J-H Park et al

1665 cholecystitis, renal cancer and cataract. The burden of osteoarthritis and congestive heart failure attributable to overweight was also correlated with age in both men and women, showing the highest level in the 50s age group but decreased in the over-60 age group. The burden of breast cancer was higher for women in their 40s. The burden of preeclampsia and post-delivery hemorrhage was higher in their 20s, and the burden of post-delivery hemorrhage, obstructed labor, birth asphyxia and birth trauma was higher in their 30s for women.

Disease burden attributable to obesity by age group The burden of disease attributable to obesity by gender and age is presented in Table 4.

In both gender, the obesity-AB reached its highest level in the 60s age groups but decreased in the over-70 age group. For men, except in their 70s, the burden of diabetes attributable to obesity was highest among other diseases in all age groups. In their 70s, the burden of ischemic heart disease was highest among other diseases. For women, the burden of diabetes was highest among other diseases in all age groups. In both gender, the obesity-AB was correlated with age for diabetes, stroke, cholecystitis, showing its highest level in the age group of 60s and a decrease in the over-70 age group. For women, ischemic heart disease-AB reached its highest level in the 60s age groups but decreased in the over-70 age group. Unlike women, men had a greater burden of ischemic heart disease attributable to obesity in their 40s. The burden

Table 3

Attributable burden of diseases due to overweight by gender and age group (unit: person years/100 000 persons)

Disease

Male

Diabetes mellitus Ischemic heart disease CVA Symptomatic gall bladder osteoarthritis Breast cancer Renal cancer Endometrial cancer Cataracts Cogestive heart failure Pre-eclampsia Maternal hemorrhage Obstructed labour Birth asphyxia and birth trauma Total

Table 4

Female

20-29

30-39

40-49

50-59

60-69

70+

20-29

30-39

40-49

50-59

60-69

70+

60.8 46.5 6.9 7.3 1.6 0.0 0.5 0.0 0.1 0.0 0.0 0.0 0.0 0.0

318.1 152.8 21.0 15.8 2.7 0.0 1.8 0.0 0.2 0.1 0.0 0.0 0.0 0.0

958.54 387.4 68.5 28.9 8.3 0.0 4.5 0.0 0.6 0.1 0.0 0.0 0.0 0.0

1321.4 641.5 137.6 45.3 20.2 0.0 5.0 0.0 0.8 0.3 0.0 0.0 0.0 0.0

1063.5 725.0 179.6 54.6 18.4 0.0 8.5 0.0 1.0 0.1 0.0 0.0 0.0 0.0

537.7 535.6 185.1 38.2 8.2 0.0 5.4 0.0 1.0 0.2 0.0 0.0 0.0 0.0

111.1 6.5 2.6 9.4 0.2 1.3 0.0 0.3 0.0 0.0 0.4 0.1 0.1 0.0

263.2 40.3 7.9 20.9 0.7 11.5 0.5 2.2 0.1 0.0 0.3 0.1 0.1 0.0

978.9 191.5 42.7 34.5 10.6 36.1 1.0 9.0 0.4 0.1 0.0 0.0 0.0 0.0

1952.5 505.4 128.5 59.2 35.7 0.0 3.5 2.8 2.3 0.4 0.0 0.0 0.0 0.0

1979.2 774.9 234.2 66.2 32.8 0.0 5.1 4.0 4.6 1.3 0.0 0.0 0.0 0.0

1223.9 617.0 244.4 38.4 6.1 0.0 3.4 1.8 1.7 1.3 0.0 0.0 0.0 0.0

123.7

512.5

2172.0

2050.8

1311.4

131.8

347.8

1304.9

2690.1

3102.1

2138.0

1456.7

Attributable burden of diseases due to obesity by gender and age group (unit: person years/100 000 persons)

Disease

Male

Female

20–29

30–39

40–49

50–59

60–69

70+

20–29

30–39

40–49

50–59

60–69

70+

Diabetes mellitus Ischemic heart disease CVA Symptomatic gall bladder osteoarthritis Breast cancer Renal cancer Endometrial cancer Cataracts Cogestive heart failure Preeclampsia Maternal hemorrhage Obstructed labour Birth asphyxia and birth trauma

24.3 15.5 20. 3.8 0.5 0.0 0.1 0.0 0.1 0.0 0.0 0.0 0.0 0.0

77.3 33.6 3.3 5.8 0.5 0.0 0.3 0.0 0.1 0.0 0.0 0.0 0.0 0.0

267.6 100.1 12.9 12.4 1.7 0.0 0.9 0.0 0.2 0.0 0.0 0.0 0.0 0.0

163.9 61.0 10.2 7.9 1.5 0.0 0.4 0.0 0.1 0.0 0.0 0.0 0.0 0.0

175.2 95.8 18.8 13.6 2.0 0.0 1.0 0.0 0.3 0.0 0.0 0.0 0.0 0.0

91.1 91.3 24.4 11.1 1.2 0.0 0.8 0.0 0.3 0.1 0.0 0.0 0.0 0.0

40.6 4.3 0.7 4.3 0.0 0.2 0.0 0.1 0.0 0.0 0.1 0.1 0.1 0.0

104.9 15.5 1.9 9.2 0.0 1.3 0.1 0.5 0.0 0.0 0.1 0.1 0.1 0.0

410.0 52.1 8.7 14.3 0.2 3.4 0.2 1.9 0.1 0.1 0.0 0.0 0.0 0.0

969.4 150.4 30.1 27.9 1.0 0.0 0.9 2.8 0.8 0.1 0.0 0.0 0.0 0.0

1098.8 252.9 60.5 35.4 1.0 0.0 1.4 4.0 2.1 0.6 0.0 0.0 0.0 0.0

456.9 128.9 40.7 14.4 0.1 0.0 0.7 1.8 0.5 0.4 0.0 0.0 0.0 0.0

Total

46.2

120.8

395.8

245.1

306.7

220.3

50.4

133.7

491.1

1183.2

1456.7

644.3

International Journal of Obesity

Burden of obesity and overweight in Korea J-H Park et al

1666 of breast cancer was higher for women in their 40s. The burden of pre-eclampsia and post-delivery hemorrhage was higher in their 20s, and the burden of obstructed labor, birth asphyxia and birth trauma was higher in their 30s.

Discussion This study employed various research methods to estimate the burden of overweight- and obesity-related diseases with the following considerations: To define overweight and obesity, firstly, this study used the categories set by WHO: a BMI between 25 and 29.9 kg/m2 was defined as overweight and a BMI of 30 kg/m2 or above as obesity.10 That is to make the results of the study comparable to those reported from a similar study in other countries, the international criteria for BMI was used. World Health Organization also recommends use of the same cutoff points for BMI values for comparison of BMI between groups and among individuals in the group.4 Thus, the results of this study are comparable with those of studies using the BMI standard developed by WHO, making a comparison between countries possible. However, recent studies have shown that Asian populations have higher risks of metabolic syndromes such as type 2 diabetes, cardiovascular disease than Caucasians.19–25 Therefore, for diabetes, ischemic heart disease, stroke, we selected studies performed in Asian population.26–28 Especially, for diabetes, ischemic heart disease, we selected studies performed in Korean population.26,28 For stroke, we selected studies performed in Chinese population29 because no study was conducted that suggests RR values of obesityinduced stroke for Korean population yet. For other overweight and obesity-related diseases, we could not use RRs suggested by studies performed in Asian population because we could not find such study meet this study’s inclusion criteria. In addition, however, for the further evaluation, cohort studies of obese Asians are critically needed to measure the disease burden attributable to obesity in Korea. Secondly, the study selected diseases attributable to overweight and obesity by conducting a systematic review. Although there are some review articles of obesity-induced diseases, no systematic review has been conducted in the same area. Therefore, findings from this study can be used as references in other studies especially that of study subjects are Asian population. In addition to a systematic review, the study also used research results of AICR (1997) to identify obesity-induced cancers. The need for the AICR study results stemmed from the fact that whilst there are numerous studies of diseases associated with obesity, the results across these studies are inconsistent or contradictory, so it is difficult to ensure a cause–effect relationship. In the process of conducting a systematic review of diseases associated with obesity, diseases and physical disabilities, including sleep apnea, were omitted because respective studies did not have International Journal of Obesity

the level of validity of evidence as required in this study (Level 2b or better of the Oxford Center for Evidence Based Medicine Levels of Evidence).17 The validity of evidence is critical in assessing the burden of disease because low levels of research evidence do not provide accurate RRs, and consequently the cause–effect relationship cannot be proven. Although this study failed to investigate all the diseases related to overweight and obesity, there could be more diseases associated with obesity. For instance, Strauss suggested the association between low self-esteem and obesity,42 but failed to quantify the cause–effect relationship. Also, this study was limited by the failure to include diseases whose incidence rate or prevalence rate is not easily estimated and those diseases whose burden cannot be quantified. This study used 2001 statistics of the cause of death, insurance claim data submitted to the Korean National Social Health Insurance Corporation, which contained only ICD-10 coded disease database. Therefore, disorders or discomforts related to overweight and obesity such as low self-esteem, physical disabilities could not included in this study because they do not have ICD-10 codes. Thirdly, RRs can be divided into two categories based on whether the study suggested RRs of incidence or RRs of mortality for the health condition resulted from obesity. The Australian Burden of Disease Study used RRs of mortality to assess the disease burden attributable to obesity.43 However, it is assumed that obesity is more related to the incidence of disease and injury than mortality, so the use of RRs of death might lead to underestimation of the burden of disease. This study used RRs of disease incidence resulted from obesity for estimating the disease burden, thereby raising the reliability of the results. The burden of disease attributable to overweight was 732.6 and 922.9 PYs per 100 000 persons in men and women, respectively. The top four categories of diseases such as diabetes, ischemic heart disease, stroke, cholecystitis accounted for 98.2% of the total disease burden. Thus the impact of overweight was dominantly seen in these four diseases while the contribution of overweight to the remaining diseases was meager. By gender, men have more burden attributable to ischemic heart disease than women (30.6% for men, 20.1% for women). On the contrary, women have more burden attributable to diabetes than men (69.1% for men, 59.4% for women). This difference between men and women was explained by the RRs of disease incidence resulted from obesity. For ischemic heart disease, RRs show no difference between different gender but, DALYs of ischemic heart disease are higher for men (345 PYs) than women (302 PYs). But for diabetes, RRs for women is almost twice higher than men but DALYs of diabetes shows little difference between men (801 PYs) and women (740 PYs). The disease burden attributable to obesity was 144.2 and 337.3 PYs per 100 000 persons in men and women, respectively. The top four categories of diseases such as diabetes, ischemic heart disease, stroke, cholecystitis accounted for

Burden of obesity and overweight in Korea J-H Park et al

1667 99.2% of the total disease burden, whereas the contribution of obesity to the remaining diseases was so small. Consistent with overweight, men have more burden attributable to ischemic heart disease than women and women have more burden attributable to diabetes than men. Women have more burden of disease attributable to overweight and obesity than men. It is mainly because diabetes accounts for highest burden in both gender and diabetes attributable to overweight and obesity are more common in women than men. That was inconsistent with the 2002 WHO report in which the disease burden attributable to overweight was higher in women. According to the WHO’s world health report 2002, diabetes was responsible for 58% of the global disease burden attributable to a BMI above 21 kg/m2, and ischemic heart disease and cancer contributed to 21% and 8–42% of the global disease burden, respectively.44 This study also demonstrated the highest obesity-AB for diabetes, in addition to a limited range of diseases for which the contribution of obesity was significant, which is consistent with the WHO report. However, this study found the contribution of obesity to diabetes is higher than WHO report. That can be explained by the difference of RRs of disease incidence especially in diabetes. WHO reports used RRs of diabetes incidence derived from studies performed in western countries, primarily in Caucasian subjects, which is lower than RRs in this study. Compared with The Australian Burden of Disease Study, the same findings observed. The reason is same; The Australian Burden of Disease Study used RRs of diabetes incidence derived from studies performed in Caucasian subjects;45–48 RRs of diabetes incidence due to overweight is 1.8 and due to obesity is 3.2 which is lower than RRs in this study. In terms of age, the proportion of burden associated with overweight and obesity increased with age for diabetes, ischemic heart disease, stroke, cholecystitis, osteoarthritis, endometrial cancer, cataract and congestive heart failure. This positive correlation between the disease burden and age was also suggested in the 2002 WHO report.44 The disease burden attributable to overweight was 827.1 PYs, which was 3.2 times higher than that attributable to obesity at 260.0 PYs. This difference was explained by the higher prevalence rate of overweight, even though the RRs of overweight are insignificant compared to those of obesity. The prevalence rate of overweight was 29.6% in men and 25.9% in women, which was 7.5 times higher than the prevalence rate of obesity of 4.0% in men and 3.4% in women.6 The impact of a higher prevalence rate of overweight is consistent with the proposition suggested by Rose et al.49 Rose stated that risk typically increases across the spectrum of a risk factor. Rose’s work led to one of the most fundamental axioms in disease prevention across risk factors: ‘A large number of people exposed to a small risk may generate many more cases than a small number exposed to high risk.’9 Other studies have proven that the incidence of complications was higher in the population with moderate

hypertension than in that with high-level hypertension.50,51 These findings demonstrate that health interventions aimed at influencing the whole population and shifting the whole distribution of a risk factor would be more effective than high-risk group-focused strategies to reduce the impact of the risk factor.52 For instance, WHO recommended the implementation of a policy to control the prices of highcalorie foods and distribution costs to reduce the disease burden attributable to obesity.44 This study was limited because it failed to quantify the burden of attributable to overweight and obesity in terms of demographic characteristics such as region and income level. Kim et al.53 reported a negative correlation between the prevalence of overweight and obesity and education levels. And the result of the present study also signals the same negative correlation between the disease burden attributable to obesity and education levels. This study, however, did not prove the association of the disease burden with demographical factors but suggested the importance of disease burden estimation based on sociodemographic variables in establishing public health strategies.

Conclusion This study used DALY to estimate disease burden attributable to overweight and obesity in Korea. The disease burden attributable to overweight was 827.1 PYs per 100 000 persons overall, 732.6 for men, 922.9 for women. The disease burden attributable to obesity was 260.0 PYs overall, 144.2 for men, 377.3 for women. Women have more burden of disease associated with overweight and obesity than men. Diabetes related to overweight and obesity accounts for highest burden among other diseases in both genders. The disease burden attributable to overweight was 3.2 times higher than that attributable to obesity This difference was explained by the higher prevalence rate of overweight. This result signifies the importance of population-based, public health interventions rather than high-risk group-focused strategies to reduce the burden of disease associated with obesity

Acknowledgements This research was supported by a grant of the Korea Health 21 R&D Project, Ministry of Health & Welfare, Republic of Korea (01-PJ1-PG1-OICH10-0007).

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