%0 Journal Article %A Johnson, Will %A Norris, Tom %A Bann, David %A Cameron, Noel %A Wells, Jonathan K %A Cole, Tim J %A Hardy, Rebecca %D 2020 %T Differences in the relationship of weight to height, and thus the meaning of BMI, according to age, sex, and birth year cohort %U https://repository.lboro.ac.uk/articles/journal_contribution/Differences_in_the_relationship_of_weight_to_height_and_thus_the_meaning_of_BMI_according_to_age_sex_and_birth_year_cohort/11841339 %2 https://repository.lboro.ac.uk/ndownloader/files/22745126 %K Benn parameter %K Body mass index %K Birth year cohort %K Secular trend %K Trajectory %X
Objective: Weight can be adjusted for height using the Benn parameter (kg/mB), where B is the power that minimises the correlation with height. We investigated how the Benn parameter changes across age (10-65 years) and time (1956 to 2015) and differs between sexes.
Methods: The sample comprised 49,717 individuals born in 1946, 1958, 1970, or 2001. Cross-sectional estimates of the Benn parameter were produced and cohort differences at ages 10/11 and 42/43 years were examined using linear regression. Multilevel modelling was used to develop trajectories showing how the Benn parameter changed over age from childhood to mid-adulthood in the three older cohorts.
Results: The Benn parameter was closest to 2 in childhood but consistently lower across adulthood, particularly in females and the most recent cohort. At ages 10/11 years, the Benn parameter was greater than 3 in both sexes in the 2001 cohort but between 2.2 and 2.7 in the three older cohorts. This difference was estimated to be +0.67 (0.53, 0.81) in males and +0.53 (0.38, 0.68) in females, compared to the 1946 cohort, and was driven by a much higher weight SD in the 2001 cohort. Conversely, at ages 42/43 years, the Benn parameter was lowest in the 1970 cohort due to a slightly lower weight-height correlation. This difference was estimated to be -0.12 (-0.34, 0.10) in males and -0.15 (-0.42, 0.13) in females, compared to the 1946 cohort.
Conclusions: Changes over time in the obesogenic environment appear to have firstly reduced the Benn parameter due to a lowering of the weight-height correlation but secondly and more drastically increased the Benn parameter due to increasing weight variation.

%I Loughborough University