Waist-to-height ratio

A person's waist-to-height ratio – occasionally written WHtR^[a] – or called waist-to-stature ratio (WSR), is defined as their waist circumference divided by their height, both measured in the same units. This dimensionless quantity is used as a predictor of obesity-related cardiovascular disease and a measure of the distribution of body fat. Higher values of WHtR indicate higher risk of obesity-related cardiovascular diseases; it is correlated with abdominal obesity.^[1]

More than twenty-five years ago, WHtR was first suggested as a simple health risk assessment tool because it is a proxy for harmful central adiposity^[2] and a boundary value of 0.5 was proposed to indicate increased risk.^[3]^[4] A WHtR of over 0.5 is critical and signifies an increased risk; a 2010 systematic review of published studies concluded that "WHtR may be advantageous because it avoids the need for age-, sex- and ethnic-specific boundary values".^[5] In April 2022, the UK's National Institute for Health and Care Excellence (a government body) proposed new guidelines which suggested that all adults "ensure their waist size is less than half their height in order to help stave off serious health problems".^[6] In September 2022, NICE formally adopted this guideline.^[7]

According to World Health Organization guidance, the waist circumference is usually measured midway between the lower rib and the iliac crest.^[8]

Guidelines

Calculation

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${\text{WHtR}}={\frac {\text{waist circumference}}{\text{height}}}$ e.g. 1: ⁠72 cm/160 cm ⁠ = 0.45

e.g. 2: ⁠36 in/72 in ⁠ = 0.50 (72" = 6'0")

Any unit will do, as long as waist and height share the same unit.

United Kingdom

The UK's National Institute for Health and Care Excellence (NICE): All adults "ensure their waist size is less than half their height in order to help stave off serious health problems".^[9] ^[10]

Recommended boundary values

The October 2022 NICE guidelines recommend boundary values for WHtR (defining the degree of "central adiposity" (abdominal obesity)) as follows:

WHtR	central adiposity	health risks	action?
0.6 or more	high	further increased	Take Action
0.5 to 0.59	increased	increased	Take Care
0.4 to 0.49	healthy	not increased	no, OK

NICE say that these classifications can be used for people with a body mass index (BMI) of under 35, for both sexes and all ethnicities, including adults with high muscle mass. The health risks associated with higher levels of central adiposity include type 2 diabetes, hypertension and cardiovascular disease. NICE have proposed the same boundary values for children of 5 years and over.^[11]

Boundary values were first suggested for WHtR in 1996 to reflect health implications and were portrayed on a simple chart of waist circumference against height. The boundary value of WHtR = 0.4 was suggested to indicate the start of the 'OK' range. The 0.5 boundary value was suggested to indicate the start of the 'Take Care' range, with the 0.6 boundary value indicated the start of the 'Take Action' range.^[12]

Simplified guidelines

The first boundary value for increased risk of WHtR 0.5 translates into the simple message "Keep your waist to less than half your height".^[13]^[14] The updated NICE guideline says "When talking to a person about their waist-to-height ratio, explain that they should try and keep their waist to half their height (so a waist-to height ratio of under 0.5)".^[10]

Age-adjusted boundary values

A 2013 study identified critical threshold values according to age, with consequent significant reduction in life expectancy if exceeded. These are: WHtR greater than 0.5 for people under 40 years of age, 0.5 to 0.6 for people aged 40–50, and greater than 0.6 for people over 50 years of age.^[15]

Public health tool

WHtR is a proxy for central (visceral or abdominal) adiposity: values of WHtR are significantly correlated with direct measures of central (visceral or abdominal) adiposity using techniques such as CT, MRI or DEXA.^[4]^[16]^[17]^[18]

WHtR is an indicator of 'early health risk': several systematic reviews and meta-analyses of data in adults of all ages,^[19]^[20]^[21]^[22] as well as in children and adolescents,^[23]^[24] have supported the superiority of WHtR over the use of BMI and waist circumference in predicting early health risk.

Cross-sectional studies in many different global populations have supported the premise that WHtR is a simple and effective anthropometric index to identify health risks in adults of all ages,^[20]^[21]^[25]^[26] and in children and adolescents.^[27]^[28]^[29]

In a comprehensive narrative review, Yoo concluded that "additional use of WHtR with BMI or WC may be helpful because WHtR considers both height and central obesity. WHtR may be preferred because of its simplicity and because it does not require sex- and age-dependent cut-offs".^[30]

As an indicator of mortality

Not only does WHtR have a close relationship with morbidity, it also has a clearer relationship with mortality than BMI.^[31]^[32]^[33]

As an indicator of central adiposity

Many cross- sectional studies have shown that, even within the normal BMI range, many adults have WHtR which is above 0.5.^[34]^[35]^[26] Many children show the same phenomenon.^[36]^[37] Risk factors for metabolic diseases^[35]^[38] and mortality are raised in these subjects.^[39]^[40]^[41]