Should arm span or height be used in calculating the BMI for the older people? Preliminary results

Abstract

Aims and objectives: To consider using arm span rather than height for calculating the body mass index, as a parameter that offers greater long-term stability, for the nutritional assessment of persons aged over 65 years.

Background: The body mass index presents certain drawbacks for the nutritional screening of older people suffering malnutrition or at risk of malnutrition, due to the anthropometric changes that occur with increasing age, especially the progressive loss of height.

Design: Observational, cross-sectional study, using nonprobabilistic convenience sampling, with anthropometric measurements and nutritional screening in older men and women, divided into two groups: (1) aged 65-75 years and (2) aged over 75 years.

Methodology: Height and arm span were measured to calculate two separate indices of body mass: body mass index (weight/height) and body mass index.1 (weight/arm span). Nutritional screening was conducted using the Mini Nutritional Assessment Short-Form, which includes the body mass index as an anthropometric measure.

Results: Our results reveal statistically significant differences between the two indices, for the sample analysed. Body mass index.1 classifies a larger number of older people as suffering malnutrition and fewer as being at nutritional risk. When this new index is used, there is a displacement of the subjects at risk, thus increasing the number considered at risk of malnutrition and in need of appropriate therapeutic intervention. Therefore, the use of body mass index.1 would enable more people suffering malnutrition, who would otherwise remain untreated, to be attended.

Conclusions: As arm span, as an anthropometric measure, remains unchanged over time, it could be used instead of height, as an alternative index (body mass index.1) to the conventional body mass index. Further research is needed to determine the association between body mass index.1 and clinical status parameters to determine optimum cut-off points.

Relevance to clinical practice: This study describes the greater stability of body mass index.1 with respect to body mass index for nutritional screening, and the resulting benefits for nutritional monitoring and intervention for older people.

Keywords: BMI; arm span; nutritional risk; nutritional status; older people.