Height diminished with age in both men and women. Weight declined with age in men but incremented in women until middle age group and then diminished in old age group.
In men, BMI was lowest in old age group than others while BMI was lowest in young age group in women. WC of men stopped to increment with age after middle age group whereas WC of women continued to grow bigger with age. WHtR incremented with age in both genders, more prominently in women than in men (Table 1).
In entire age group, the prevalence of MS was higher in women (19.1%) than in men (12.3%). And the prevalence of MS incremented with advancement in age in both genders, more steeply in women (Figure 1).
B. AUCs of each obesity indicator for metabolic syndrome
In entire age group, AUC of WHtR was the largest one among 3 obesity indicators for MS in men and women (Table 2). After adjusted for age, no significant difference was found among three obesity indicators for MS in both genders (Table 3). When compared within three different age groups, for young, middle-aged and elderly men and young-aged women, there was no significant difference in AUC among three obesity indicators. For middle-aged and elderly women AUC of WHtR and WC were similar with each other but significantly larger than BMI’s (Table 4).
8
9
-Table 2. Comparison of the AUC for obesity indicators regarding metabolic syndrome for entire age (n=6,160).
BMI WC WHtR
Men (n=2,584) 0.70 (0.68-0.71) 0.75 (0.73-0.76)a 0.76 (0.743-0.77)b
Women (n= 3,576) 0.78 (0.76-0.79) 0.82 (0.81-0.84) a 0.84 (0.83-0.86) b, c
Values are presented AUCs (95% CI). AUC estimated by ROC analysis.
AUC, area under the receiver-operating characteristics curve
Within a row, P < 0.01 for the following comparisons of AUC: a BMI v. WC, b. BMI v. WHtR, c. WC v. WHtR
Table 3. Comparison of the AUC for obesity indicators regarding metabolic syndrome: adjusted for age as continuous variable.
BMI WC WHtR
Men (n=2,584) 0.75 (0.73-0.77) 0.77 (0.75-0.79) a 0.76 (0.75-0.78)
Women (n= 3,576) 0.86(0.85-0.87) 0.87 (0.86-0.88) 0.87 (0.86-0.88)
Values are presented AUCs (95% CI). AUC estimated by ROC analysis.
AUC, area under the receiver-operating characteristics curve
Within a row, P < 0.01 for the following comparisons of AUC: a BMI v. WC, b. BMI v. WHtR, c. WC v. WHtR
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Table 4. Comparison of the AUC for obesity indicators regarding metabolic syndrome according to age group (n=6,160).
BMI WC WHtR
Men (n=2,584 )
19-39 yr (n=933 ) 0.80 (0.78-0.83) 0.82 (0.79-0.84) 0.83 (0.81-0.85)
40-60yr (n=1,051) 0.68 (0.66-0.71) 0.71 (0.69-0.74) 0.71 (0.68-0.74)
61+ yr (n=600) 0.68 (0.65-0.72) 0.71 (0.67-0.75) 0.69 (0.66-0.73)
Women (n= 3,576)
19-39 yr (n=1,282) 0.92 (0.91-0.94) 0.92 (0.91-0.94) 0.93 (0.91-0.94)
40-60yr (n=1,368) 0.78 (0.76-0.81) 0.82 (0.79-0.84) a 0.82 (0.80-0.84) b
61+ yr (n=926) 0.69 (0.66-0.72) 0.74 (0.71-0.77) a 0.72 (0.69-0.75) b
Values are presented AUCs (95% CI). AUC estimated by ROC analysis.
AUC, area under the receiver-operating characteristics curve
Within a row, P < 0.01 for the following comparisons of AUC: a BMI v. WC, b. BMI v. WHtR, c. WC v. WHtR
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Fig. 1. Prevalence of metabolic syndrome.
* Value is significantly different from each other by chi-square test. (p<0.05)
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III. DISCUSSION
We compared three anthropometric obesity indices in terms of prediction for MS by using data from the Fourth Korea National Health and Nutrition Examination Surveys (KNHANES IV). While WHtR was better predictor for MS than other anthropometric obesity indices in entire age group, there was no difference among three obesity indices after adjusted for age. After stratification of subjects according to age, three obesity indices had similar predictability in men and young women while only BMI showed inferior predictability for MS in middle-aged and elderly women.
MS is considered as stronger risk factor than any individual risk factors for morbidity (Isomaa et al., 2001) and mortality of cardiovascular disease.(Malik et al., 2004) Compared with individuals with no risk factors, those with one to two syndrome factors had higher risk for cardiovascular mortality (Hazard ratio = 1.7) and if they had the full metabolic syndrome – three to five risk factors, Hazard ratio is even higher 2.7. Ho reported that both cardiovascular and all-cause mortality increases as the number of MS risk factors increases.
(Ho et al., 2008) This finding is supported by other study.(Ford, 2004) Therefore, to estimate more accurate cardiovascular risk, we investigated ROCs of obesity indices with MS rather than individual risk factor as a surrogate for morbidity and mortality of CVD.
Previous studies (Schneider et al., 2007), (Can et al., 2009), (Hsieh and Muto, 2006) have reported WHtR has the highest level of predictability for MS among obesity indicators in entire age group, which is consistent with findings from our study. Many studies (Ho et al., 2003), (Lee et al., 2008a), (Park et al., 2009),(Hsieh et al., 2003) reported WHtR is superior predictor to WC and BMI for WHtR is more correlated with cardiovascular risk factors such
- 13 -
as hypertension, diabetes, dyslipidemia and proposed that height is so important parameter that height should be taken into consideration in predicting cardiovascular risk more precisely.
Schneider made an intriguing remark in his paper, questioning the superiority of WHtR.
When he did compare BMI, WC and WHtR after dividing subjects into 3 separate age groups (20–44yr, 45–65yr, and 66–79yr), comparison among AUCs of 3 obesity indices revealed no differences in each separate age group, even though, the AUC for WHtR for MS was significantly greater than others in entire age group.(Schneider et al., 2007) This observation is also in agreement with results of our research. When compared within 3 different age groups, three obesity indices showed similar predictability in men and young women and even WHtR was not superior to WC in middle aged and elderly women group.
Adjusting WC with height does not seem to offer better predictability for cardiovascular risk than WC alone.
Anthropometric indices changes with aging. Height grows smaller due to osteoporotic change in vertebrae constantly with age that is positively correlated with CVD risk factors.(Hsieh et al., 2003),(Hsieh et al., 2000) First National Health and Nutrition Examination Survey Epidemiologic Follow-Up Study tracking 13,031 men and women for 13 years, found no relation between height and CVD when age and years of education were adjusted for(Liao et al., 1996), suggesting age may account for the height-CVD relation as a key confounder. This finding is reinforced by the Framingham Heart Study.(Kannam et al., 1994)
When previous studies calculated AUCs of anthropometric indices, they analyzed entire age group all together without considering age related changes in anthropometric parameters, In systemic review of 78 studies(Browning et al., 2010), most studies showed, age adjusted
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odd ratio for diabetes and CVD of 3 obesity indices were similar each other and age adjusted odd ratio for cardiovascular risk factor of WC and WHtR were similar with each other but higher than BMI’s like our studies.
For we calculated AUC of obesity indices for metabolic syndrome by gender and age groups, our result reflected the effects of age-related change in anthropometry on the relationship between obesity indicators and cardiovascular risk.
Previously observed trend of inverse association between height and cardiovascular morbidity might be mostly due to a confounding relation of height with age.(Liao et al., 1996)
In the present study, when compared within three age groups, BMI had lowest predictability for MS in middle-aged and elderly women but BMI had similar predictability with WHtR in the other groups. In women, increasing parity and menopause was associated with increase in fat mass and redistribution of fat to abdominal area and decrease in lean body mass.(Stevens et al., 2010) But BMI reflects only body weight and cannot discriminate between lean body mass and fat mass especially after menopause, so that its validity for CVD risk prediction depreciate in middle-aged and elderly women.
We used data from a cross-sectional survey which only allows showing the association between obesity indices and MS at present and is not good enough to investigate the future CVD risk for clinical implication. To calculate precise future cardiovascular risk with obesity index, longitudinal study should be conduct as a next step of our research.
Subjects of our study were large nationwide samples of Korean population. Most previous investigations were not nationally sampled and less representative for general population for most of them recruited the volunteers from neighborhood groups(Can et al., 2009), primary care setting(Schneider et al., 2007),clinic for regular health checkup.(Hsieh and Muto, 2006)
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IV. CONCLUSION
In conclusion, there is no superiority among obesity indicators to predict MS – the best surrogate for CVD risk in men and young women, which is a misunderstanding originated from ignoring the effect of aging on anthropometric parameters. BMI has less predicting power for MS in middle-aged and elderly women than WC and WHtR. In the future, longitudinal studies should be carried out to assess future cardiovascular risk by using anthropometric obesity indices.
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- 21 - - 국문요약 –
대사 증후군을 예측하는 가장 유용한 비만 지표
아주대학교 대학원 의학과 김 수 연
(지도교수: 김 범 택)
연구 배경: 최근에는 허리둘레-신장비가 심혈관계 질환의 위험을 예측하는 데 있어 체질량지수와 허리둘레보다 더 우수한 지표라는 연구결과들이 발표되고 있다. 본 연구는 성별과 연령에 따라 대사 증후군을 가장 잘 예측할 수 있는 비만의 지표를 규명하고자 하였다.
방법: 2008년도 1월부터 12월까지 시행된 제 4기 2차년도 국민건강영양조사에 참여한 19세 이상의 성인 6,610명을 대상으로 단면적 연구를 시행하였다.
비만지표들의 예측력을 비교하기 위해 대사증후군에 대한 각 지표들의 areas under the receiver-operating characteristics curves (AUC)를 분석하였다.
결과: 전체 연령에서 볼 때, 남녀 모두 대사증후군에 대한 허리둘레-신장비의 AUC가 가장 높았다. 그러나 연령을 보정한 후에는 세 개의 비만 지표의 예측력 간에 차이가 없었다. 세 개의 다른 연령 군으로 분류하여 비교했을 때 남성과 19-39세 여성에서는 세 개의 비만 지표의 예측력에 차이가 없었다. 40-60세
- 22 -
여성과 61세 이상의 여성 군에서는 허리둘레-신장비와 허리둘레의 AUC는 서로 유사했으며 체질량지수의 AUC는 이보다 낮았다.
결론: 남성과 19-39세 여성 군에서는 대사증후군을 예측하는 데 있어 비만지표들 사이에 우위가 없다. 40-60세와 61세 이상의 여성 군에서는 체질량지수가 허리둘레, 허리둘레-신장비보다 낮은 예측력을 보였다.
핵심어: 허리둘레-신장비, 허리둘레, 체질량지수, 대사증후군