History, haldanes and health inequities: exploring phenotypic changes in body size by generation and income level in the US-born White and Black non-Hispanic populations 1959-1962 to 2005-2008.

BACKGROUND: Most public health literature on trends in population health and health inequities pertains to observed or targeted changes in rates or proportions per year or decade. We explore, in novel analyses, whether additional insight can be gained by using the 'haldane', a metric developed by evolutionary biologists to measure change in traits in standard deviations per generation, thereby enabling meaningful comparisons across species and time periods.
METHODS: We analysed the phenotypic embodied traits of body height, weight and body mass index of US-born White and Black non-Hispanic adults ages 20 to 44 as measured in six large nationally representative population samples spanning from the 1959-1962 National Health Examination Survey I to the 2005-2008 National Health and Nutrition Examination Survey. Setting the former as baseline, we computed the haldane for each outcome for each racial/ethnic group for each survey, overall and stratified by family income quintile.
RESULTS: For height, high rates of phenotypic change (haldane ≥ 0.3) occurred chiefly between 1960 and 1980, especially for the Black population in the higher income quintiles. By contrast, for weight, high rates of phenotypic change became evident for both the White and Black populations in the late 1980s and increased thereafter; for body mass index, the shift to high rates of change started in both groups in the late 1990s, especially in the middle income quintiles.
CONCLUSIONS: Our results support use of the haldane as a supplemental metric to place changes in population health and health inequities in a larger biological and historical context.