Letters COMMENT & RESPONSE adults and children, especially in large numbers, such as the Gemini cohort (the sample used in our study ). It is also the In Reply We thank Jaffer et al for their comments about the role most commonly used measure of adiposity, allowing for com- of parental education as a moderator of genetic risk for child- parison with future studies and meta-analyses. In relation to hood obesity. In our recently published article showing that ethnicity, only 5% of those who completed the home environ- the heritability of body mass index (BMI) was higher for chil- ment measure identified as nonwhite. This was too small to dren living in a more obesogenic home environment, there allow us to undertake analyses stratified by ethnicity. We thank were indeed differences in parental education according to the Dissanayake for suggesting epigenetic factors as a potential home environment measure. Parental education is a well- mechanism involved in the development of childhood obe- established risk factor for childhood obesity, and previous stud- sity. This area of research is of great interest to many obesity ies have shown that the heritability of BMI in childhood var- researchers but was not the focus of this study, and epigen- ies according to parental education, with lower heritability etic data are not available in this sample. estimates observed for children whose parents had higher edu- cational attainment. However, what is less clear is the mecha- Stephanie Schrempft, PhD nism through which parental education influences child- Moritz Herle, PhD hood obesity risk. Our study goes beyond parental education Clare H. Llewellyn, PhD to measure directly key aspects of the home environment that have been hypothesized to play a causal role in childhood obe- Author Affiliations: Department of Behavioural Science and Health, University sity. Although there were differences in parental education ac- College London, London, United Kingdom (Schrempft, Llewellyn); University cording to the home environment measure, there was still con- College London Great Ormond Street Institute of Child Health, London, United Kingdom (Herle). siderable overlap; 40% of mothers living in a higher-risk home Corresponding Author: Clare H. Llewellyn, PhD, Department of Behavioural environment were classified as highly educated compared with Science and Health, University College London, 1-19 Torrington Place, London 58% of mothers living in a lower-risk home environment. This WC1E 6BT, United Kingdom (firstname.lastname@example.org). indicates that the differences in heritability estimates cannot Published Online: April 1, 2019. doi:10.1001/jamapediatrics.2019.0376 be entirely explained by the differences in parental educa- Conflict of Interest Disclosures: None reported. tion. In addition, parental educational level is not a feasible 1. Schrempft S, van Jaarsveld CHM, Fisher A, et al. Variation in the heritability modifiable target for public health interventions; rather, the of child body mass index by obesogenic home environment. JAMA Pediatr. specific environmental exposures captured in the home en- 2018;172(12):1153-1160. doi:10.1001/jamapediatrics.2018.1508 vironment measure (eg, food availability in the home) need to 2. Silventoinen K, Huppertz C, van Beijsterveldt CE, Bartels M, Willemsen G, be targeted. Therefore, in our view, parental education can- Boomsma DI. The genetic architecture of body mass index from infancy to adulthood modified by parental education. Obesity (Silver Spring). 2016;24(9): not be used as a proxy measure for the complex environment 2004-2011. doi:10.1002/oby.21588 that is the family home. 3. Wardle J, Carnell S, Haworth CM, Plomin R. Evidence for a strong genetic We thank Dissanayake for highlighting the validity of BMI influence on childhood adiposity despite the force of the obesogenic as a measure of adiposity. Our research group has previously environment. Am J Clin Nutr. 2008;87(2):398-404. doi:10.1093/ajcn/87.2.398 validated parent-report measures of the heights and weights 4. Adab P, Pallan M, Whincup PH. Is BMI the best measure of obesity? BMJ. 2018; of twin children by examining the correlations between par- 360:k1274. doi:10.1136/bmj.k1274 ent and researcher measures in a sample of 228 families (height: 5. van Dijk SJ, Molloy PL, Varinli H, Morrison JL, Muhlhausler BS; Members Pearson r = 0.90; weight: Pearson r = 0.83). Body mass in- of EpiSCOPE. Epigenetics and human obesity. Int J Obes (Lond). 2015;39(1):85- dex remains the most feasible way to estimate adiposity in 97. doi:10.1038/ijo.2014.34 jamapediatrics.com (Reprinted) JAMA Pediatrics Published online April 1, 2019 E1 © 2019 American Medical Association. All rights reserved.
JAMA Pediatrics – American Medical Association
Published: Jun 1, 2019
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