- Waist circumference is an important predictor of health risk.
- Waist circumference should be measured at the top of the iliac crest.
- Waist circumference is the best anthropometric measure of intra-abdominal fat and changes to it.
Waist Circumference and Health Risk
Jean Vague was the first to recognize the harmful health consequences of excess abdominal fat over 50 years ago (1). Since this initial observation, a great deal of research has strengthened abdominal obesity’s independent association with diabetes, hypertension, cardiovascular disease, some cancers, and mortality risk (2-5). It is now acknowledged that waist circumference increases health risk beyond that explained by body mass index (BMI) alone (6-9).
Health-related Waist Circumference Cut-offs
Abdominal obesity is commonly assessed using waist circumference, and common measurement protocols include the visible narrowing of the waist, last rib, top of the iliac crest, or the midpoint between the last rib and the iliac crest. Current Canadian clinical practice guidelines and the National Institutes of Health (NIH) in the United States recommend measuring waist circumference using the iliac crest as the landmark (10, 11). Accordingly, the International Chair on Cardiometabolic Risk also recommends measuring waist circumference at the top of the iliac crest. The NIH has published sex-specific waist circumference thresholds (men: 102 cm, women: 88 cm) to denote increased health risk within each BMI category (11). However, unlike BMI categories, these waist circumference cut-offs were not based on their association with morbidity or mortality, but were instead based on waist circumference values corresponding to a BMI of 30 kg/m2 in Caucasian men and women. These waist circumference thresholds seem appropriate for non-Hispanic blacks and Mexican Americans (12), but are likely too high for most Asian populations (13) and are unknown for other ethnic groups. The appropriate cut-offs for determining health risk in Asian and other ethnic populations are still being studied, but reported values for Asians range from 85 to 90 cm for men and 80 to 90 cm for women (13). For instance, the International Diabetes Federation position statement on the metabolic syndrome and its clinical diagnosis has lowered waist girth values to 94 cm for European men, while recognizing the need to propose cut-offs specific to various ethnic populations.
Within a given BMI category, individuals with a waist circumference greater than the proposed thresholds generally have a worse metabolic profile than individuals with a waist circumference below these thresholds (6). Moreover, high waist circumference predicts a later decline in insulin sensitivity over a 5 year follow-up (7). It has also been reported that once waist circumference is taken into account, BMI does not provide any added information in terms of predicting metabolic risk (8). For these reasons, it is important to measure waist circumference when assessing health risk.
Measuring Waist Circumference—Health Care Professionals
Measure waist circumference with the measuring tape directly on the individual’s skin (Figure 1). Ask the individual to loosen and/or remove any restrictive garments or clothing that would interfere with the measure. The individual should be relaxed with their arms crossed on their chest and their feet shoulder-width apart. To ensure proper landmarking, mark the measurement site (i.e., iliac crest) on the right side of the individual’s body with a horizontal line after determining the correct location. The International Chair on Cardiometabolic Risk recommends that you palpate the iliac crest firmly with your hands and place the landmark at the uppermost border of the iliac crest. The bottom edge of the tape measure should be placed directly level with the landmark. Ensure the tape is horizontal to the floor, is snug without indenting the individual’s skin, and is not twisted or caught on clothing. Measure the waist at the end of a normal expiration to the nearest 0.1 cm.
The literature suggests that waist circumference measures are highly repeatable and that measures between trained technicians are very comparable (14, 15). Proper training helps to position the measurement tape properly and apply constant tension, which ensures an accurate assessment of waist circumference. The use of spring-loaded measurement tapes (Figure 2) can improve accuracy by ensuring that constant tension is applied to the tape while waist circumference is being measured.
Measuring Waist Circumference—Self-measurement
It is recommended that you measure waist circumference in front of a mirror in your undergarments or without any clothing that would interfere with the measurement (Figure 3). Measure your waist circumference with the measuring tape directly on your skin. Stand in a relaxed position with your feet shoulder-width apart. The use of a Myotape is recommended to ensure proper landmarking and measurement. Use your hands to find the uppermost border of your hip bones on both sides of your body. Align the bottom edge of your measuring tape with the top of your hipbones. Use the mirror to ensure that you have placed the measuring tape correctly (i.e., horizontally, and not twisted or caught on clothing). The measure should be snug without indenting your skin. Relax and measure your waist at the end of a normal expiration to the nearest 0.1 cm.
Errors associated with self-reported waist circumference
Men and women tend to underestimate their waist size when it is measured using a traditional measuring tape, with the underestimation increasing with waist size (16). Consequently, only 35.5% of abdominally obese men (>102 cm) and 44.9% of abdominally obese women (>88 cm) correctly classified themselves into the highest health risk category. However, when the same individuals used a tape measure with a spring mechanism, the measurement error dropped to 0.5 cm and 0.4 cm in men and women respectively, and only 2% of the sample misclassified their waist circumference category. This suggests that spring-loaded tape measures may be a useful clinical tool for minimizing the underestimation of waist circumference and may provide an accurate method for self-assessment of health risk.
Association Between Waist Circumference and Intra-abdominal Fat
Increases in abdominal fat are largely responsible for increases in waist circumference. Abdominal fat can be divided into two major components: subcutaneous fat and intra-abdominal fat. Subcutaneous fat lies just below the skin and is outside the abdominal muscle wall, whereas intra-abdominal (visceral) fat is located inside the abdominal muscular wall and lies in between the organs or viscera. Waist circumference is a good correlate of both total abdominal fat and its sub-compartments. However, the importance of waist circumference in predicting health risk is more commonly thought to be due to the relationship between waist circumference and intra-abdominal fat. Indeed, waist circumference is a stronger predictor of intra-abdominal fat than BMI (17-23). Because intra-abdominal fat is a strong independent predictor of morbidity (24-27) and mortality (28), considerable attention has been given to the ability of waist circumference to predict intra-abdominal fat.
Previous studies have reported that the percentage of error for estimates of intra-abdominal fat using waist circumference is roughly 25 to 35% (18-21). Factors such as age, gender, race, and fitness partly explain the variation in the amount of intra-abdominal fat for a given waist circumference (29-31). These differences in the amount of intra-abdominal fat for a given waist circumference may explain why different waist cut-offs are needed for men and women and for different racial groups. For example, Filipino women with a waist circumference of 80 cm would be expected to have 22% more intra-abdominal fat than Caucasian women and 35% more intra-abdominal fat than African American women with the same waist circumference (31).
Age is another factor that greatly influences the amount of intra-abdominal fat for a given waist circumference. An older man (>50 years of age) with a waist circumference of 102 cm would be expected to have 70% more intra-abdominal fat than a 25 year old man with the same waist circumference, and 140% more intra-abdominal fat than a 25 year old woman (29) (Figure 4). However, how these differences translate into specific waist circumference cut-offs for various populations is unclear.
Association Between Changes in Waist Circumference and Intra-abdominal Fat
Waist circumference is also commonly used to assess changes in abdominal obesity, and is a stronger predictor of changes in intra-abdominal fat than waist-to-hip ratio (23, 32, 33). Changes in waist circumference are associated with changes in intra-abdominal fat in response to diet and/or exercise-induced weight loss (Figure 5) (23, 32-34). Although the exact amount of intra-abdominal fat loss for a given reduction in waist circumference varies considerably (33), reductions in waist circumference are likely to reduce intra-abdominal fat. Exercise can often reduce intra-abdominal fat and waist circumference, even if it does not reduce body weight significantly (35-40). Accordingly, waist circumference should be measured as part of interventions aimed at reducing intra-abdominal fat and related health risk.
Waist circumference is a strong predictor of health risk beyond that explained by BMI alone. This may be partly due to the strong ties between waist circumference and intra-abdominal fat. Indeed, waist circumference is the strongest anthropometric predictor of intra-abdominal fat and changes to it. Because abdominal obesity has such a harmful impact on one’s health, it is important to routinely measure waist circumference in the clinical assessment of cardiometabolic risk.
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