The challenges of accurate waist and hip measurement over clothing: Pilot data

Summary

Background

Accurate waist and hip measurement are increasingly central to the goal of weight control and the battle against diabetes and cardiovascular disease. Protocols and methods vary widely, with little guidance on clothing. This pilot study investigated the effect of light clothing on measurement.

Aims

To determine whether light clothing and underwear make a potentially clinically significant difference of 0.5 cm to the measurement of waist and hip circumference in a group of volunteer subjects.

Methods

We measured waist circumference over light clothing and then over bare skin. We measured hip circumference over light clothing and then over underwear and with a small sub-group, on bare skin.

Results

50 volunteers were measured. Potentially clinically significant differences were found in the mean values as followed (mean; 95% CI): light clothing compared to bare skin at the waist (0.50 cm; −1.54 to 2.55 cm); light clothing compared to underwear at the hip (2.58 cm; −0.75 to 5.91 cm).

Conclusion

This study demonstrates that the effect of clothing on waist and hip measurements is not always trivial, and deserves a larger study. Waist circumference measurements should be made on bare skin whenever possible and hip circumference measurements over underwear.

Introduction

Waist circumference (WC) and hip circumference (HC) measurements are increasingly advocated in clinical practice and epidemiology. A WC of ≥94 cm in males and ≥80 cm in females correlates with being overweight (BMI ≥ 25 kg/m²) according to WHO guidelines [1]. Alternately, these measures identify individuals with a normal BMI but a high waist/hip ratio, an indicator of central obesity and a risk factor for developing diabetes and CVD [2]. A meta-analysis examining WC/waist:hip ratio and their relationship with CVD found that for both genders, each 1 cm increase in WC increased the relative risk of a CVD event by 2%. A 0.01 unit hip/waist ratio increase was associated with a 5% rise in CVD relative risk [3]. Over a range of BMIs, individuals with high WCs are at increased risk of developing type-II diabetes [4]. High WCs and narrow HCs are also associated with cardiovascular risk factors [5], [6].

Waist circumference is a clinically important anthropological measurement because evidence has shown that BMI can be inaccurate in predicting obesity in non-European origin ethnic groups. South Asians in particular are known to be at higher risk of insulin resistance. It is essential that these measurements are taken accurately [7]. Protocols for measurement, however, vary as there is no universally accepted method. Wang et al. found 14 different descriptions of where the waist should be measured [8].

Clothing is another problem. Within the standardised WHO MONICA study examining cardiovascular diseases some centres measured participants wearing light clothing, others over underwear and in one case, underwear with a standardised paper coat [9].

A literature search in OVID Medline was done to assess protocols regarding clothing using the following search strategy for the period 2000–2007:

$$\begin{array}{l}[(\text{waist measure}\$.\text{tw})\text{OR}(\text{waist circumference}\$.\text{tw})]\hfill \\ \text{AND}\hfill \\ [(\text{hip measure}\$.\text{tw})\text{OR}(\text{waist circumference}\$.\text{tw})]\hfill \end{array}$$

We found no publications researching the effects of clothing and underwear on WCs and HCs, although many papers give advice. Of 51 papers no studies compared the effects of layers of clothing on circumference measurements. Of 15 studies mentioning clothing, 11 favoured ‘light clothing,’ without defining ‘light clothing’. One study measured over underwear [10], another over bare skin [11] and one measured either over light clothing or underwear [12]. One multi-centre study undertook some measurements over underwear and others over light clothing [13].

It seems important to know if clothing protocol is of clinical significance to the measurements. The aim of this pilot study was to assess how much WC and HC measurements were affected by different layers of clothing. We compared measurements on bare skin to measuring with underwear and light clothing. A difference of 0.5 cm was considered to be clinically significant as this could change what category of waist or hip measurement a person is considered to be in if the measurements are rounded to the nearest centimetre e.g. 93.5 would be rounded to 94, which is overweight on WHO criteria. Our prior hypothesis was that light clothing would increase the circumference of both waists and hips by a clinically significant degree but underwear would not.