Declare waist circumference vital sign in clinical practice: IAS/ICCR Consensus Statement

Prevalence of abdominal obesity

• Although the prevalence of obesity measured by BMI might have plateaued in some countries, the prevalence of abdominal obesity as measured by waist circumference is generally increasing.
• The lack of inclusion of waist circumference in global obesity surveillance might inadequately characterize the health risk associated with the global obesity prevalence, as it seems that the prevalence of abdominal obesity is increasing.
• Current obesity prevalence trends based on BMI alone should be interpreted with caution. We recommend that serious consideration should be given to the inclusion of waist circumference in obesity surveillance studies.

Identifying the high-risk obesity phenotype

• In categorical analyses, waist circumference is associated with health outcomes within all BMI categories independent of sex and age.
• When BMI and waist the circumference is considered as continuous variables in the same risk prediction model, waist circumference remains a positive predictor of the risk of death, but BMI is unrelated or negatively related to this risk.
• The strength of the association between waist circumference and morbidity and/or mortality is not fully realized until after adjustment for BMI.
• The improved the ability of waist circumference to predict health outcomes over BMI might be at least partially explained by the ability of waist circumference to identify adults with increased VAT mass.
• We recommend that measurements of waist circumference and BMI should become a standard part of clinical encounters (that is, an accepted 'vital sign').

Waist circumference and risk prediction

• The combination of BMI and waist circumference identifies a high-risk obesity phenotype better than either measure alone.
• We recommend that waist circumference should be measured in clinical practice as it is a key driver of risk; for example, many patients have altered CVD risk factors because they have abdominal obesity.
• Waist circumference is a critical factor that can be used to measure the reduction in CVD risk after the adoption of healthy behaviours.

Changes in waist circumference in response to treatment

• Exercise and/or diet consistent with guideline recommendations are associated with substantial reductions in waist circumference, independent of age, sex or ethnicity.
• Available evidence from RCTs suggests that exercise is associated with substantial reductions in waist circumference, independent of the quantity or intensity of exercise.
• Exercise-induced or diet-induced reductions in waist circumference are observed with or without weight loss.
• We recommend that practitioners routinely measure waist circumference as it provides them with a simple anthropometric measure to determine the efficacy of lifestyle-based strategies designed to reduce abdominal obesity.

Measurement of waist circumference

• Currently, no consensus exists on the optimal protocol for measurement of waist circumference and little scientific rationale is provided for any of the waist circumferences protocols recommended by leading health authorities.
• The waist circumference measurement protocol has no substantial influence on the association between waist circumference, all-cause mortality and CVD-related mortality, CVD and T2DM.
• Absolute differences in waist circumference obtained by the two most often used protocols, iliac crest (NIH) and midpoint between the last rib and iliac crest (WHO), are generally small for adult men but are much larger for women.
• The classification of abdominal obesity might differ depending on the waist circumference protocol.
• We recommend that waist circumference measurement are obtained at the level of the iliac crest or the midpoint between the last rib and iliac crest. The protocol selected to measure waist circumference should be used consistently.
• Self-measures of waist circumference can be obtained in a straightforward manner and are in good agreement with technician-measured values.

Values of waist circumference to estimate the health risk

• From the evidence available, we question the rationale behind current guidelines recommending that a single waist circumference threshold for white adults (men >102 cm; women >88 cm) be used to denote a high waist circumference, regardless of BMI category.
• We recommend that prospective studies using representative populations are carried out to address the need for BMI category-specific waist circumference thresholds across different ethnicities (such as those proposed in Table 1 for white adults). This recommendation does not, however, diminish the importance of measuring waist circumference to follow changes over time and, hence, the utility of strategies designed to reduce abdominal obesity and associated health risk.

"Health professionals should be trained to properly perform this simple measurement and should consider it as an important vital sign to assess and identify, as an important treatment target in clinical practice" concluded the authors.

"Waist circumference as a vital sign in clinical practice: a Consensus Statement from the IAS and ICCR Working Group on Visceral Obesity," is published in the journal Nature Reviews Endocrinology.