SES-of-Origin and BMI in Youth: Comparing Germany and Minnesota

Behavior Genetics (2019) 49:24–48 https://doi.org/10.1007/s10519-018-9938-7 ORIGINAL RESEARCH SES-of-Origin and BMI in Youth: Comparing Germany and Minnesota Wendy Johnson1 · Elisabeth Hahn2 · Juliana Gottschling3 · Franziska Lenau4 · Frank M. Spinath2 · Matt McGue5,6 Received: 11 December 2017 / Accepted: 8 November 2018 / Published online: 29 November 2018 © The Author(s) 2018 Abstract Increasing obesity is a world-wide health concern. Its most commonly used indicator, body mass index (BMI), consistently shows considerable genetic and shared environmental variance throughout life, the latter particularly in youth. Several adult studies have observed less total and genetically influenced variance with higher attained SES. These studies offer clues about sources of the ‘obesity epidemic’ but analogous youth studies of SES-of-origin are needed. Genetic and environmental influences and moderating effects of SES may vary in countries with different health policies, lifestyles, and degrees/sources of social inequality, offering further clues to the sources of the obesity epidemic. We examined SES-of-origin moderation of BMI variance in the German TwinLife study’s cohorts assessed around ages 5, 11, 17, and 23–24, and in the Minnesota Twin Family Study’s (MTFS) 11- and 17-year-old birth cohorts assessed longitudinally around ages 11, 17, and 23–24, comparing male and female twins and their parents. Age for age, both sexes’ means and variances were greater in MTFS than in TwinLife. We observed that SES generally moderated genetic influences, more strongly in females, similar to most adult studies of attained-SES moderation of BMI. We interpreted differences in our SES-of-origin observations in light of inevitably-missing covariance between SES-of-origin and BMI in the models, mother-father and parent–offspring BMI correlations, and parental attained-SES–BMI correlations. We suggest that one source of the present obesity epidemic is social change that amplifies expression of genes both constraining SES attainment and facilitating weight gain. Keywords SES-of-origin · BMI · Obesity · Overweight · Youth · National differences Edited by Tinca Polderman. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10519-018-9938-7) contains supplementary material, which is available to authorized users. * Wendy Johnson 1 Department of Psychology, University of Edinburgh, 7 George Square, Edinburgh EH8 9JZ, UK 2 Department of Psychology, Saarland University, Saarbrücken, Germany 3 Cognitive Science & Assessment, University of Luxembourg, Luxembourg City, Luxembourg 4 Jugendwerk St. Josef – Haus Maria Rosenberg, Waldfischbach‑Burgalben, Germany 5 Department of Psychology, University of Minnesota, Minneapolis, USA 6 Department of Epidemiology, Biostatistics and Biodemography, University of Southern, Denmark, Odense, Denmark 13 Vol:.(1234567890) Overweight and obesity are increasing worldwide health concerns. The World Health Organization (WHO; WHO 2017) estimated that, in 2016, 39% of adults (39% of men, 40% of women) over 18 years old were overweight, and onethird (11% of all men and 15% of all women) of those were obese. The WHO reported that the 2016 rates were nearly triple those in 1975 and showed no signs of slowing. The terms ‘overweight’ and ‘obesity’ refer to accumulation of abnormal or excessive adipose tissue that may impair health, with obesity being more extreme and its associated risks thus greater. Obesity is associated with cardiovascular diseases such as heart disease and stroke (the leading cause of death in 2015 and 2012 according to the WHO), Type 2 diabetes (also experiencing sky-rocketing rates worldwide), musculoskeletal diseases such as osteoarthritis, and many of the most common cancers, including breast and prostate. Importantly, obesity is usually preventable [Global Burden of Obesity Collaborators (GBOC) 2017; WHO 2017], suggesting that risks and prevalences of the diseases associated with it can be effectively limited by preventing obesity in the first place. Development of overweight inevitably Behavior Genetics (2019) 49:24–48 precedes obesity because excess adipose tissue accumulates over time. Consistent with this, rates of overweight and obesity in children are lower than in adults, and lower in adults of younger than older ages, at least until late adulthood (GBOC 2017). Nonetheless, obesity rates in children have also been increasing rapidly (WHO 2017). GBOC (2017) estimated that, in 2015, 5% of children under 18 were obese, and this rate had increased in recent years more rapidly than that in adults. Though data on age-related patterns of obesity development are sparse, the available evidence suggests that, age for age, more recently born cohorts are accumulating adipose tissue more rapidly, The earlier in life adiposity becomes excess, the more likely a person is to become obese and to encounter its associated health problems (e.g., Emmett and Jones 2015; Johnson et al. 2015; Langstrom et al. 2008). This implies that it is especially important to identify and understand the processes underlying adiposity accumulation in childhood and youth. There is very consistent evidence for substantial but far from deterministic genetic influences on propensities both to carry and accumulate adipose tissue throughout the lifespan (e.g., Albuquerque et al. 2017; Fernandez et al. 2012; Hjelmborg et al. 2008; Sillventoinen et al. 2010). This is also the case for factors that can influence adiposity accumulation such as food preferences (e.g., Reed et al. 2006), metabolic rates (e.g., Muller and Geisler 2017), and physical activity levels (e.g., de Geus et al. 2014). Both total amounts and proportions of variance attributable to genetic influence, however, vary considerably with age, over time, with country level economic development and rate thereof, and ambient obesity level (e.g., Min et al. 2013). Along with the current ‘obesity epidemic’, the consistent evidence for substantial non-shared environmental as well as genetic influences, and for shared environmental influences in children and youth, this attests to the importance of understanding the involved genetic and environmental interplay (e.g., Albuquerque et al. 2017). Obesity prevalence patterns, economic wealth and socioeconomic status, and Simpson’s Paradox Though obesity is a problem worldwide, rates vary considerably among countries, and often among regions within countries. Countries and regions within them with higher levels of education and greater economic wealth tend to have higher rates (GBOC 2017; WHO 2017), though there are also many exceptions to this (for example, Samoa runs a very high rate, while Japan’s rate is low). Perhaps seemingly paradoxically, however, within most ‘economically developed’ regions with high rates, individuals with greater education and personal wealth [higher socioeconomic status 25 (SES)] tend to have l (...truncated)