In older people, the use of body mass index (BMI) to determine nutritional status is often unreliable. In particular, the accuracy of height measurement may be impeded by age-related spinal deformities, such as kyphosis (curvature of the spine), alterations in height and shape of the vertebral discs, and vertebral compression. A number of studies have demonstrated that other skeletal measurements might be employed as alternatives to height when assessing the older age groups. Arm-span has been shown to approximate to height at maturity in Caucasian populations and is relatively independent of ageing, suggesting that it may offer an alternative to height in calculating BMI in older populations. Also, it is an inexpensive and simple measurement to obtain in a field setting. However, there are few equations developed for determining height from arm-span in African populations and these are often based on small samples.
A recent study set out to examine the differences in the relationship between height and arm-span in four ethnic groups in Ethiopia. In addition, the study determined BMI using arm-span cut-off values (BMIas) equivalent to conventional BMI which uses height cut-off values (BMI-ht), for chronic energy deficiency.
The study took place in four regions in Ethiopia, namely Oromo, Amhara, Tigray and Somali regions. A total of 706 Ethiopians aged 18-50 years from four different ethnic groups were measured. Anthropometric measurements (weight, height and armspan)2 were obtained using standard techniques. BMIs using arm-span (BMI-as) and height (BMI-ht) were calculated. T-tests were performed to compare means, and linear regression employed to investigate the relationship between BMI-ht and BMI-as.
Both ethnic and sex differences in the relationships between height and armspan and their derived variables (BMI-as and BMI-ht) were found. Armspan measurements exceeded height measurements in all the ethnic groups and in both sexes. Armspan and height and their corresponding BMI-as and BMI-ht were highly correlated in all ethnic groups. BMI-as cut-offs equivalent to the conventional BMI-ht classification of chronic energy deficiency were similar in the Oromo, Amhara and Tigre groups, but substantially higher in the Somalis.
Armspan can be used as a proxy for height to estimate BMI, however the relationship between the two measures varies considerably with ethnicity and sex. Unless sex and ethnicity specific cut-offs are applied, the use of BMI-as using conventional cut-off points will over-estimate the prevalence of underweight in these populations.
In order to estimate true height from arm-span in elderly people, it is necessary first to establish the relationship between these two measurements in a younger population of the same ethnicity. The authors propose that this study has achieved this for Ethiopia, since the four ethnic groups studied together make up more than 85% of the Ethiopian population. It is therefore possible to use the relationships identified to estimate height from arm-span in older Ethiopians in whom height cannot be measured accurately. However, additional research is needed to determine similar anthropometric differences in other groups, in Africa and in other regions of the world.
1 De Lucia.E, Lemma.F, Tesfaye.F, Demisse.T and Ismail.S (2002): The use of armspan measurement to assess the nutritional status of adults in four Ethiopian ethnic groups. European Journal of Clinical Nutrition: vol 56, pp 91-93
2 A 3 m long steel tape measure was used for the armspan measurement. Armspan was measured while the subject was standing erect and looking straight ahead, with their back against the wall to provide support. The arms were outstretched at right angles to the body with palms facing forwards. The measurements were taken from one middle fingertip to the other middle fingertip, with the tape passing in front of the clavicles. Two field workers supported the elbows.