The genetic and environmental influences on childhood obesity: a systematic review of twin and adoption studies

Abstract

In this systematic review, we aimed to collect together all previous twin and adoption studies on childhood and adolescent obesity up to the age of 18 years. Using several sources, we identified nine twin and five adoption studies; all of these studies had used relative weight as an indicator of obesity. Except the two twin studies from the Korean population, all studies represented Caucasian populations. In a meta-analysis of these twin studies, we found that genetic factors had a strong effect on the variation of body mass index (BMI) at all ages. The common environmental factors showed a substantial effect in mid-childhood, but this effect disappeared at adolescence. Adoption studies supported the role of family environment in childhood obesity as correlations were found between adoptees and adoptive parents; however, correlations were substantially stronger between parents and their biological offspring, further supporting the importance of genetic factors. In the future, more studies implementing genetic and environmental measures into twin models are needed as they allow estimation of the proportion of total genetic variation explained by candidate genes and analyses of gene-environment interactions. More studies of genetic architecture in non-Caucasian populations, of gene-environment interactions, and of body composition and body fat distribution are needed. IntroductionChildhood obesity is one of the major public health problems in the modern world. In the period [2003][2004][2005][2006], 32% of the US children were classified as obese or overweight, 1 and increasing trends in childhood obesity are seen all over the world. 2 These results are especially alarming as overweight children show a high risk of becoming obese adults. 3,4 Childhood is an important period of life for health interventions as health-related behaviors are just in formation, and it seems possible to intervene for preventing the development of obesity. 5 Thus, it is crucial to further understand the background mechanisms of childhood obesity to find even more effective measures to prevent it before it begins to produce more or less irreversible health damages.Both genetic and environmental factors will probably contribute to childhood obesity. 6 Family studies have shown that obesity runs in families, although more detailed twin, adoption and family studies have shown that genetic differences between individuals explain a major proportion of the within-population variation in body mass index (BMI, kg m À2 ) in adulthood. [7][8][9] It is probable that genetic factors have an important role in childhood obesity also, but their role may be different or they may result from other genes than those that operate in adulthood. 10 The environmental factors shared by family members, such as co-twins in twin studies, have shown only a slight effect on the variation of adult BMI. 7,8 However, they may have a more important role in childhood, where parents and their offspring live together and where siblings obviously have a much greater opportu...

Evidence that BMI and type 2 diabetes share only a minor fraction of genetic variance: a follow-up study of 23,585 monozygotic and dizygotic twins from the Finnish Twin Cohort Study

“…At the onset of the current study, less than 5% of the twins reported having lived with their co-twin after the age of 25 years (data not shown). Lack of influence of shared environment after adolescence has been observed, among other things, for food use [21], BMI [22] and physical activity [23].…”

Causes and consequences of obesity: the contribution of recent twin studies

“…5--12 The majority of MZ twin pairs are very similar for BMI (intraclass correlations 0.8 in FinnTwin16 at age 25) 13 and the difficulty in identifying distinctively discordant pairs underscores the strong genetic component to BMI and the predisposition to obesity. This has been demonstrated for adults in adoption, family and twin studies, 14,15 but less so for childhood obesity 16 and rate of weight gain. 16,17 Here, we review the discordant twins' growth patterns and development of obesity, measures of physical activity and metabolic rates, and the physiological consequences of acquired obesity as can be identified through clinical and imaging studies ( Figure 1).…”

“…This has been demonstrated for adults in adoption, family and twin studies, 14,15 but less so for childhood obesity 16 and rate of weight gain. 16,17 Here, we review the discordant twins' growth patterns and development of obesity, measures of physical activity and metabolic rates, and the physiological consequences of acquired obesity as can be identified through clinical and imaging studies ( Figure 1). In addition, we have included insights from global analysis of adipose tissue transcriptomics and lipidomics to further elucidate the metabolical and physiological changes associated with acquired obesity (Figure 2).…”

Childhood overweight after establishment of the gut microbiota: the role of delivery mode, pre-pregnancy weight and early administration of antibiotics

“…[1][2][3][4] In addition to the genetic risk, other factors may promote the transmission of risk within families, among which the transfer of the maternal gut microbiota to the child during delivery has recently received particular attention on the basis of several lines of evidence.…”