Original reportsA Comparison between BMI and Conicity Index on Predicting Coronary Heart Disease: The Framingham Heart Study
Introduction
Obesity has been observed to be positively related to the risk factors for CHD, such as hypertension, hyperlipidemia, glucose intolerance and diabetes 1, 2, 3, 4, 5, 6, 7, 8 as well as to mortality 9, 10, 11, 12, 13, 14, 15. The American Heart Association has reclassified obesity as a major, modifieable risk factor for CHD (8). Abdominal body fat is highly correlated with mortality and morbidity for CVD, diabetes, and obesity 16, 17, 18, 19, 20, 21, 22, 23 and more strongly associated with CHD risk factors than BMI. The true etiology of CHD may be more closely linked to abdominal obesity than to overall adiposity 24, 25.
BMI is highly correlated with body weight and poorly correlated with height (26) and is frequently used as a measure of body fatness in large epidemologic studies (27). A study done by Huang and colleagues revealed that abdominal adiposity, measured by waist to hip ratio (WHR) and by waist circumference was strongly associated with prevalent CHD and independent of BMI among elderly Japanese-American men (25). Another index of abdominal adiposity, the conicity index (CI), is a function of abdominal girth, weight, and height (28). The formula for the CI is:where abdominal girth is in meters, weight (Wt) in kg, and height (Ht) in meters. Valdez and colleagues (28) claimed that CI has several advantages over the WHR: (i) it has a theoretical range; (ii) it includes a built-in adjustment of waist circumference for height and weight, allowing direct comparisons of abdominal adiposity between individuals or even between populations; and (iii) it does not require the hip circumference to assess fat distribution.
A study done by Kim and colleagues (29) assessed the association of biological markers, including cholesterol, HDL, LDL, triglycerides, ApoA-1, and ApoB, with estimates of the body composition, including the CI, BMI, bioelectrical impedance analysis, and WHR. In that study one hundred-twenty-six African American adults (43 males, 83 females) from a public housing community in the District of Columbia were recruited. Among the four anthropometric indicators, the WHR provided the best explanation of the variances in biological markers, including cholesterol and ApoB levels in females. The CI showed relationships with log triglyceride levels in females, while percentage body fat (%BF) explained the variances of log HDL and log ApoA-1 in males. For cholesterol, log triglycerides and ApoB, mean values were positively associated with tertiles of the WHR, whereas mean values of log HDL and log ApoA-1 were negatively associated with tertiles of %BF. Among females the WHR and CI, indicators of relative body fat distribution, were more related to risk factors for CVD and diabetes than was the BMI.
The purpose of the study was to assess associations of adiposity (e.g., BMI and CI) with incidence as well as mortality from CHD. For this study, data from the Framingham Heart Study (FHS) was analyzed in order to examine the relationship of both mortality and incidence of CHD with BMI and CI.
Section snippets
The Cohort
The FHS cohort includes 5209 noninstitutionalized white men and women, aged 30 to 62 at study entry, who were followed biennially after entry in 1948 to the 16th examination period. Among 5209 adults, 1882 men, and 2373 women had waist measurement at the 4th examination period. Weight measured on the 4th visit and height on the 5th visit were used to calculate BMI and CI.
Exclusion Criteria
Since we were following the subjects who have BMI and CI at the 4th visit, we excluded subjects who missed waist measurement
Results
Characteristics of men and women of FHS according to quartiles of BMI and CI at the 4th visit for each sex were shown in Table 1, Table 2, Table 3, Table 4. As the BMI increased, the mean waist increased significantly for both males and females . The mean age was not significantly different across the quartiles of BMI in males but increased in females . As the CI increased, the mean age was significantly older for both males and females .
Discussion
BMI has been widely used as an index of body composition for epidemiologic studies 30, 31, 32, 33. From time to time, however, various indexes appear to challenge BMI. Some risk factors of CHD were more associated with the abdominal fat distribution 16, 17, 18, 19, 20, 21, 22, 23, 29. Since WHR is more sensitive to the abdominal fat distribution and more highly correlated with CI than BMI (29) in Black women, CI was investigated as a possible risk factors related to CHD incidence and mortality.
Acknowledgements
This research was supported in part by grant N97/10 from Office of Research Administration, Howard University.
This article used data supplied by the National Heart, Lung, and Blood Institute, NIH, DHHS from the Framingham Heart Study. The views expressed in this paper are those of the author and do not necessarily reflect the views of the National Heart, Lung, and Blood Institute or of the Framingham Study.
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