Sex-specific height-correction of weight in a population with ethnic groups that differ in stature—the SAMINOR 1 Survey: a cross-sectional study

Abstract

Background: Body mass index (BMI, weight/height²) is a common proxy for body fatness, but it is negatively correlated with height, particularly in women. In Norway, the ethnic Sami people, and especially women, have had higher BMI than their non-Sami peers. However, Sami and non-Sami differ substantially in stature. This article aimed to examine if previous findings of higher obesity measures in Sami compared to non-Sami persist when applying an adequately height-corrected weight index.

Methods: We estimated a sex-specific height-corrected weight index—the Benn index—that is, weight/height^p where p is estimated from log(weight)-log(height) regression. We used data on 15 717 men and women aged 30 and 36–79 years who participated in the SAMINOR 1 Survey (2003–2004). Correlations between height and weight and the indices BMI and Benn index were calculated using Pearson’s correlation coefficient.

Results: Sami were on average 5.8 cm shorter than non-Sami. BMI and height had a modest, negative correlation that was stronger in women than in men. Analyses were stratified by sex due to a statistically significant interaction (sex * log(height), p<0.001). There was no interaction with ethnicity (ethnicity * log(height), p=0.07 in women and p=0.24 in men). The p (95% confidence interval) in Benn index (weight/height^p) was estimated to 1.29 (1.21, 1.38) in women and 1.90 (1.83, 1.98) in men. Higher BMI in Sami compared to non-Sami was most evident in women, but Benn index did not differ by ethnicity in either sex.

Conclusion: Previous findings of higher obesity prevalence in Sami than in non-Sami may be biased. Future studies should take into account the marked height differences between these groups when comparing obesity indices.