Abstract
Many anthropometric measures such as body mass index, waist circumference, waist-to-height ratio and waist-to-hip ratio are used in epidemiological studies to define overweight and obesity, estimate body fat distribution and identify people at elevated obesity-related health risk. This paper aims to describe the usefulness of anthropometric indicators to predict cardiometabolic risk in clinical practice.
Body mass index has been used as a universal criterion of overweight (≥25 kg/m2) and obesity (≥30 kg/m2) in the general population.1 Measurements of abdominal fat distribution such as waist circumference (WC), waist-to-hip ratio (WHR) and waist-to-height ratio (WHtR) also are encouraged and may be more accurate in predicting cardiometabolic risk.2, 3 These measurements are helpful for identifying high-risk groups/populations that may benefit from target interventions such as lifestyle modification.4, 5 However, most of the thresholds for these anthropometric measures have been identified from studies of predominantly European-derived populations; therefore, different ethnic-specific cutoffs need to be investigated further.
There is evidence of racial/ethnic differences in the relationship between anthropometric measurements and adiposity, CVD risk factors and risk of mortality. African American women seem to have lower amounts of visceral adipose tissue (VAT) for a given WC, BMI, or WHR compared to white women.6-10 Furthermore, middle-aged and older African American men and women may have lower visceral fat than Hispanics and white men and women, regardless of BMI and WC measurements.11 Asians tend to have a lower BMI than whites but more health risks at lower levels of BMI.12 Thus, a given anthropometric measurement (BMI and WC) may represent different amounts of visceral fat accumulation in different racial/ethnic groups and may have implications for defining metabolic risks in different populations.11
Anthropometric thresholds for predicting CVD risk
Data from 10,969 participants in the National Health and Nutrition Examination Survey (1988-1994) were analyzed to determine WC cutoffs for CVD risk in non-Hispanics blacks, Mexican Americans and non-Hispanics. The study showed that WC is a better indicator of CVD risk than BMI across three race-ethnicity groups and clarified the importance of WC as a CVD predictor. Also, the study provided WC cutoffs as clinical action thresholds that correspond to BMI of 25 kg/m2 and 30 kg/m2 (89cm and 101cm for men, and 83cm and 94cm for women). The authors suggest the WC cutoff proposed could be rounded to 90cm and 100cm for men and to 85cm and 95cm for women.13
A cross-sectional, population-based study was conducted with 7,981 Canadians from five different provinces to test the NIH BMI/WC guidelines as a screening tool for increase health risk. The study showed that in women already at increased health risk because of an elevated BMI, the additional measurement of WC may help identify cardiovascular risk.14 A study using data from the Canadian Heart Health Survey, in which the majority of the participants were white, identified optimal BMI and WC thresholds for CVD risk of 26 kg/m2 and 91cm for men and 24 kg/m2 and 78cm for women.15
Additional studies
Another cross-sectional study with 6,476 participants, including African Americans and whites, identified thresholds for CVD risk at a BMI of 30 kg/m2 in all sex-by-ethnicity groups except for African American women (~33 kg/m2). The optimal WC threshold was 99cm for men, 92cm for white women and 97cm for African American women.16
Waist circumference provides a measurement of body fat distribution, and it is associated with abdominal adipose tissue deposits as well as total fat mass.17-21 Since visceral adipose tissue (VAT) is more metabolically active than other adipose tissue sites,22 it appears to contribute to many metabolic abnormalities associated with increment in anthropometric measurements and increase in body fat due to weight gain.19, 23-27 The relative contribution of intra-abdominal fat mass to total body fat is influenced by sex, age, race/ethnicity, physical activity and total adiposity.28 Precise measurement of VAT requires radiological imaging techniques. Because of the complexity and cost of these procedures, the use of WC is recommended for identification of adults with elevated cardiometabolic risk factors.16 However, many people have argued that using waist circumference as a single value to assess abdominal obesity without adjustments for different heights may not be as accurate, because people with similar WC but different heights may not have the same cardiometabolic risk.29
A systematic review and meta-analysis including data on more than 300,000 individuals around the world revealed that WHtR was a better predictor for obesity-related cardiometabolic risk compared to BMI and WC for both sexes.3 Similar results were obtained from a study with 244,266 Chinese adults in which WHtR and WC were better indicators of CVD risk factors than BMI.30 A mean boundary value was proposed for WHtR of 0.5 for men and women after a systematic review of 78 studies investigating WHtR and WC or BMI as predictors of diabetes and CVD among Caucasian, Asian and Central American volunteers.31 Many authors convert this boundary to the simple message, “Keep your waist circumference to less than half your height.”
Another tool to assess relative body fat distribution is the waist-to-hip ratio, for which the cutoff is 0.95 for men and 0.80 for women.32 Although this measure may be useful for risk assessment,33 it is not helpful in practical risk management because both waist and hip circumferences can decrease with weight reduction and so the ratio tends to remain the same.31
Obesity risks: Practical recommendations
The prevalence of obesity in the U.S. and worldwide has risen to epidemic proportions. The risks associated with overweight and obesity are related to abdominal fat and adverse health consequences such as cardiometabolic diseases. The assessment of adiposity and the identification of people at elevated obesity-related risk must be emphasized in clinical practice. There is no consensus about the best anthropometric measure to assess cardiometabolic risk. Although BMI, WC and WHtR measurements are practical screening tools for assessing adiposity and identifying individuals at high risk who should be targeted for lifestyle intervention and weight loss.
Although waist circumference is a good anthropometric indicator to evaluate central obesity and cardiometabolic risk, no set of boundary values would fit all ages and ethnic-specific groups. And for individuals with the same waist circumference but different heights, the cardiometabolic risk might change. WHtR has the convenience that, by making allowances for height, the same boundary value (0.5) can be used for everyone.40
Table 1 summarizes thresholds for abdominal obesity (WC) recommended by several authors and a number of national and international organizations by different racial/ethnical groups.
Conclusion
The most effective anthropometric tool for cardiometabolic risk screening must be both practical and accurate. WC is a simple and clinically effective anthropometric measure associated with cardiometabolic risk factors. WHtR is also a simple tool to assess cardiometabolic risk factors and may be more accurate than WC for risk identification across different populations. Both measurements are useful tools to complement BMI measurement for the clinical management of obesity. These tools require only the purchase of an appropriate tape measure and simple training of health-care professionals and/or assistants.
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