Waist-to-height ratio as an indicator of 'early health risk': simpler and more predictive than using a 'matrix' based on BMI and waist circumference

Abstract

Objectives: There is now good evidence that central obesity carries more health risks compared with total obesity assessed by body mass index (BMI). It has therefore been suggested that waist circumference (WC), a proxy for central obesity, should be included with BMI in a 'matrix' to categorise health risk. We wanted to compare how the adult UK population is classified using such a 'matrix' with that using another proxy for central obesity, waist-to-height ratio (WHtR), using a boundary value of 0.5. Further, we wished to compare cardiometabolic risk factors in adults with 'healthy' BMI divided according to whether they have WHtR below or above 0.5.

Setting, participants and outcome measures: Recent data from 4 years (2008-2012) of the UK National Diet and Nutrition Survey (NDNS) (n=1453 adults) were used to cross-classify respondents on anthropometric indices. Regression was used to examine differences in levels of risk factors (triglycerides (TG), total cholesterol (TC), low-density lipoprotein (LDL), high-density lipoprotein (HDL), TC: HDL, glycated haemoglobin (HbA1c), fasting glucose, systolic (SBP) and diastolic blood pressure (DBP)) according to WHtR below and above 0.5, with adjustment for confounders (age, sex and BMI).

Results: 35% of the group who were judged to be at 'no increased risk' using the 'matrix' had WHtR ≥ 0.5. The 'matrix' did not assign 'increased risk' to those with a 'healthy' BMI and 'high' waist circumference. However, our analysis showed that the group with 'healthy' BMI, and WHtR ≥ 0.5, had some significantly higher cardiometabolic risk factors compared to the group with 'healthy' BMI but WHtR below 0.5.

Conclusions: Use of a simple boundary value for WHtR (0.5) identifies more people at 'early health risk' than does a more complex 'matrix' using traditional boundary values for BMI and WC. WHtR may be a simpler and more predictive indicator of the 'early heath risks' associated with central obesity.

Keywords: PUBLIC HEALTH.

Figure 1

Categorisation of risk category of all participants by waist-to-height ratio (WHtR) and by the ‘matrix’. WHtR: green = ‘no increased risk, WHtR <0.5, (29%), yellow = ‘increased risk’, WHtR ≥0.5 to <0.6,) (44%) and red = ‘very high risk’, WHtR 0.6+, (27%). The‘ matrix’: blue = ‘not applicable/underweight’ (1%) green = ‘no increased risk’ (41%), yellow = ‘increased’ and ‘high risk’ (32%) and red = ‘very high risk’ (26%).

Figure 2

Percentage of participants who have waist-to-height ratio (WHtR) ≥0.5 and ≥0.6 within different categories of the ‘matrix’. Vertical columns denote risk by the 'matrix’: ‘not applicable’; ‘no increased risk’, ‘increased’ and ‘high risk’ and ‘very high risk’. Colours within vertical columns denote risk by WHtR: green = ‘no increased risk’ (WHtR <0.5), yellow = ‘increased risk’ (WHtR ≥0.5 to <0.6) and red = ‘very high risk’ (WHtR ≥0.6).

Figure 3

Participants with ‘healthy’ body mass index (BMI) divided according to waist-to-height ratio ≥0.5. Means for high-density lipoprotein (HDL) cholesterol and the ratio of total cholesterol: HDL cholesterol were statistically different (p<0.05) when adjusted for sex, age and BMI.