Does BMI generated by self-reported height and weight measure up in older adults from middle-income countries? Results from the study on global AGEing and adult health (SAGE)

Abstract

BackgroundSelf-reported (SR) body mass index (BMI) values are often used to determine obesity prevalence. However, individuals frequently overestimate their height and underestimate their weight, resulting in artificially lower obesity prevalence rates. These patterns are especially apparent among older adults and overweight individuals. The present cross-sectional study uses nationally representative datasets from five countries to assess the accuracy of SR BMI values in diverse settings.MethodsSamples of older adults (≥50 years old) and comparative samples of younger adults (18–49 years old) were drawn from five middle-income countries (China, India, Mexico, Russian Federation, and South Africa) in the World Health Organization’s Study on global AGEing and adult health (SAGE). Participant-reported and researcher-obtained height and weight measures were used to calculate SR and measured BMI, respectively. Paired t-tests assessed differences between SR and measured BMI values by country. Linear regressions examined the contribution of measured weight and age to differences between SR and measured BMI.ResultsSignificant differences between SR and measured BMI values were observed (p < 0.05), but the direction of these discrepancies varied by country, age, and sex. Measured weight significantly contributed to differences between SR and measured BMI in all countries (p < 0.01). Age did not contribute significantly to variation in BMI discrepancy, except in China (p < 0.001).ConclusionsThese results suggest that SR BMI may not accurately reflect measured BMI in middle-income countries, but the direction of this discrepancy varies by country. This has considerable implications for obesity-related disease estimates reliant on SR data.

Indexing adult obesity by waist-to-height and weight-to-height ratios

“…The mean height is also steadily decreasing with age but with gaining in pace past the maturity (see Figure 1). Senescence, manifested in the height reduction, [4,7] may be a contributing factor for advanced age adults and elderly, but it hardly explains the steady increase of WCHR obesity threshold with age. One plausible explanation is the survival of individuals tolerant to central obesity.…”

“…On the other hand, in senescence, a drastic reduction in both weight and height, as observed, should be attributed to a loss of lean mass. [4,7] While the weight exhibits overall a declining trend, WC has a tendency to rise. The intrinsic differences between the two measures seem to be conferred onto the BMI measures and WCHR.…”

“…With age people tend to gain weight or, in frailty, become shorter. [4,7] Also, people like to be if not healthier then at least appear slimmer and taller, or they are socially pressured into understating their weight and overstating height. [8,39] The above would be sufficient to opt for WCHR in BMI 2 stead, but adiposity is also more squarely explained by WCHR.…”

“…[2] While this classification is adopted in many countries, some interpretations intended to address ethnical or racial aspects exist, notably with respect to Asian populations where the thresholds are generally lower. [3,4] Using 20 kg/m 2 instead of 18.5 kg/m 2 as a reference point for BMI transition from underweight to healthy is convenient for interval equalisation, and is conventional when the focus is on categories above the normal/healthy. [5] Besides, the prevalence of underweight is usually negligible comparing to other BMI categories, [4] particularly in the population selected for the current study, probably because such an existence challenges the physiological limits, and in fact the healthy weight minimum should satisfy this criterion.…”

“…[3,4] Using 20 kg/m 2 instead of 18.5 kg/m 2 as a reference point for BMI transition from underweight to healthy is convenient for interval equalisation, and is conventional when the focus is on categories above the normal/healthy. [5] Besides, the prevalence of underweight is usually negligible comparing to other BMI categories, [4] particularly in the population selected for the current study, probably because such an existence challenges the physiological limits, and in fact the healthy weight minimum should satisfy this criterion. [1] Instead of using 20 kg/m 2 by convention, underweight in obesity studies are often consensually included with the healthy weight category, so that no minimum for the healthy weight is set.…”