Summary: The genetic influence on weight is halved when children are raised in a home environment where healthy eating and exercise is encouraged, a new study reports.
A healthy home environment could help offset children’s genetic susceptibilities to obesity, according to new research led by UCL.
The study, published this week in JAMA Pediatrics, found that the impact of genetic factors on weight is roughly halved if a child is bought up in a less ‘obesogenic’ home environment where healthy eating and exercise is more prevalent.
Researchers collected data on Body Mass Index (BMI) and home environments from 925 twin pairs in the British Gemini cohort. The twins’ families were asked in detail about many aspects of their home diet, physical activity, and media environments, such as the amount of healthy food in the home, how about how many media devices there were in the home and family media viewing habits.
This information was used to create a score for each home that indicated if it was a ‘high-risk’ or ‘low-risk’ environment for obesity. Of the 925 twin pairs, 508 were living in healthier, ‘low-risk’ home environments and 417 were living in less healthy ‘high-risk’ home environments.
“Our study is the first to examine how the early home environment relates to a child’s genetic susceptibility to being overweight, even though it is widely believed to be a key influence on weight,” said first author, Dr Stephanie Schrempft (UCL Behavioural Science and Health).
“The finding that genetic influence on weight was stronger among children living in riskier home environments supports a theory, developed by our group, that genetic susceptibility to obesity will be most highly expressed when individuals are living in a obesogenic environment that encourages excess consumption and low physical activity. In other words, ‘the genetic background loads the gun, but the environment pulls the trigger’.”
The researchers used the twin design to estimate the genetic and environmental influence on the BMI of children in both high- and low-risk obesogenic home environments. A third of the group consisted of identical twins who are 100% genetically the same, and two-thirds of fraternal twins who are approximately 50% genetically the same. Comparing the two types of twins allowed researchers to estimate genetic and environmental influence on BMI.
If identical twins are much more similar than fraternal twins for BMI, genes are important in shaping it. If the two types of twins are fairly similar for BMI despite their genetic differences, the home environment is an important factor.
Researchers found a much larger difference in similarity between identical and fraternal twins when children were bought-up in a high-risk home environment, indicating a greater genetic influence on children’s BMI in an obesogenic environment. In contrast, in a low-risk home environment, both types of twins were much more similar, highlighting that a healthy home environment can override genetic influence on BMI.
In the high risk environment, genetic differences between children explained 86% of differences in children’s BMI. In the low risk environment, genetic differences between children were less important in explaining differences in their BMI, accounting for only 39% of BMI differences.
Dr Clare Llewellyn (UCL Behavioural Science and Health) senior author, said: “We have known for decades that genes help to explain why people differ in their weight, but this often leads to the misconception that weight can’t be changed. This study shows that genes are not destiny when it comes to weight. In childhood, the home family environment seems to influence the extent to which genetic predisposition to a lower or higher weight is fully expressed.”
In particular, for children growing up in a healthy home food environment, genetic influence on weight was fairly modest, and the home environment was just as important. Ironically, this study points more than anything to the importance of the early environment for shaping a child’s weight.”
Funding: This work was supported by an Impact studentship to Dr Schrempft and Cancer Research UK grant.
Source: Rowan Walker – UCL
Publisher: Organized by NeuroscienceNews.com.
Image Source: NeuroscienceNews.com image is adapted from the UCL news release.
Original Research: Open access research for “Variation in the Heritability of Child Body Mass Index by Obesogenic Home Environment” by Stephanie Schrempft, PhD; Cornelia H. M. van Jaarsveld, PhD; Abigail Fisher, PhD; Moritz Herle, PhD; Andrea D. Smith, PhD; Alison Fildes, PhD; and Clare H. Llewellyn, PhD in JAMA Pediatrics . Published October 1 2018.
Variation in the Heritability of Child Body Mass Index by Obesogenic Home Environment
The early obesogenic home environment is consistently identified as a key influence on child weight trajectories, but little research has examined the mechanisms of that influence. Such research is essential for the effective prevention and treatment of overweight and obesity.
To test behavioral susceptibility theory’s hypothesis that the heritability of body mass index (BMI) is higher among children who live in more obesogenic home environments.
Design, Setting, and Participants
This study was a gene-environment interaction twin study that used cross-sectional data from 925 families (1850 twins) in the Gemini cohort (a population-based prospective cohort of twins born in England and Wales between March and December 2007). Data were analyzed from July to October 2013 and in June 2018.
Parents completed the Home Environment Interview, a comprehensive measure of the obesogenic home environment in early childhood. Three standardized composite scores were created to capture food, physical activity, and media-related influences in the home; these were summed to create an overall obesogenic risk score. The 4 composite scores were split on the mean, reflecting higher-risk and lower-risk home environments.
Main Outcomes and Measures
Quantitative genetic model fitting was used to estimate heritability of age-adjusted and sex-adjusted BMI (BMI SD score, estimated using British 1990 growth reference data) for children living in lower-risk and higher-risk home environments.
Among 1850 twins (915 [49.5%] male and 935 [50.5%] female; mean [SD] age, 4.1 [0.4] years), the heritability of BMI SD score was significantly higher among children living in overall higher-risk home environments (86%; 95% CI, 68%-89%) compared with those living in overall lower-risk home environments (39%; 95% CI, 21%-57%). The findings were similar when examining the heritability of BMI in the separate food and physical activity environment domains.
Conclusions and Relevance
These findings support the hypothesis that obesity-related genes are more strongly associated with BMI in more obesogenic home environments. Modifying the early home environment to prevent weight gain may be particularly important for children genetically at risk for obesity.