Education modifies genetic and environmental influences on BMI

Socio-economic differences in body mass index: the contribution of genetic factors

BACKGROUND

Higher mean body mass index (BMI) among lower socioeconomic position (SEP) groups is well established in Western societies, but the influence of genetic factors on these differences is not well characterized.

METHODS

We analyzed these associations using Finnish health surveys conducted between 1992 and 2017 (N = 33 523; 53% women) with information on measured weight and height, polygenic risk scores of BMI (PGS-BMI) and linked data from administrative registers to measure educational attainment, occupation-based social class and personal income.

RESULTS

In linear regressions, largest adjusted BMI differences were found between basic and tertiary educated men (1.4 kg/m2, 95% confidence interval [CI] 1.2; 1.6) and women (2.5 kg/m2, 95% CI 2.3; 2.8), and inverse BMI gradients were also found for social class and income. These SEP differences arose partly because mean PGS-BMI was higher and partly because PGS-BMI predicted BMI more strongly in lower SEP groups. The inverse SEP gradients of BMI were steeper in women than in men, but sex differences were not found in the genetic contributions to these differences.

CONCLUSIONS

Better understanding of the interplay between genes and environment provides insight into the mechanisms explaining SEP differences in BMI.

Is education level, as a proxy for socio-economic position, related to device-measured and self-reported sedentary behavior in European older adults? A cross-sectional study from the SITLESS project

Background

Sedentary behavior (SB) is a determinant of health in older adult people. Educational level is a primary driver of health disparities and is demonstrated to be a reliable measure of socioeconomic position. We aimed to examine the associations between educational level and self-reported along with device-measured SB in older adults living in Europe and the association of mentally active and passive SB domains with the educational level and gender in these associations.

Methods

The design is cross-sectional. One thousand three hundred and sixty participants aged 65 and over (75.3±6.3 years old, 61.8% women) participated. Inclusion criteria were scored with the Short Physical Performance Battery. Variables that describe the sample were assessed with an interview, and device-measured SB was assessed with an accelerometer. SB was assessed with the Sedentary Behavior Questionnaire and an accelerometer. Multiple linear regression models were used to study the association between the level of education and SB.

Results

Participants self-reported an average of 7.82 (SD: 3.02) daily waking hours of SB during weekend days, and the average of device-measured SB was 11.39 (1.23) h. Total mentally active SB (weekdays and weekends) was associated with the education level (p < 0.000). Participants were more sedentary during the week than during weekends, regardless of level of education (p < 0.000). Education level was significantly associated with self-reported mean hours per day in 46SB (p = 0.000; R=0.026; 95%CI).

Conclusion

Low education level in older adults is associated with self-reported SB but not with objective SB measures.

Weight change in a national cohort of U.S. Military Veterans engaged in medication treatment for opioid use disorder

Medication treatments for opioid use disorder (MOUD) save lives and improve outcomes for countless individuals. However, data suggest the potential for significant weight gain during methadone treatment and little is known about weight change during buprenorphine treatment. Using Veteran Health Administration administrative data from fiscal year 2017 to fiscal year 2019, two cohorts were created: 1) Veterans diagnosed with opioid use disorder (OUD) taking methadone (N = 1425); and 2) Veterans diagnosed with OUD taking buprenorphine (N = 3756). Linear mixed models were used to analyze weight change during the first MOUD treatment episode in the observation period. Random slopes and intercepts were included in the model to estimate variation in BMI across individuals and time. The data revealed a slight upward trend in BMI over the course of treatment. Specifically, a daily increase of 0.004 for Veterans in methadone treatment and 0.002 for Veterans in buprenorphine treatment was observed. This translates to a gain of about 10 pounds over the course of 1 year of methadone treatment and 5 pounds for 1 year of buprenorphine treatment for a Veteran of average height and weight. The amount of weight gain in methadone treatment is significantly less than other published findings, but nonetheless indicates that assessment and discussions between patients and providers related to weight may be warranted.

Joint Consideration of Means and Variances Might Change the Understanding of Etiology

Twin and adoption studies compare the similarities of people with differing degrees of relatedness to estimate genetic and environmental contributions to trait population variance. The analytic workhorse of these kinds of variance-focused designs is the intraclass correlation, which estimates similarity between pairs of individuals. Group means, by contrast, play no overt role in estimating genetic and environmental influences. Although this focus on variance has made very important contributions to understanding psychological characteristics, we contend that the exclusion of mean effects from behavioral genetic designs may have obscured key environmental influences and impeded full appreciation of the ubiquity and nature of gene-environment interplay in human outcomes. We provide empirical examples already in the literature and a theoretical framework for thinking through the incorporation of mean effects using largely forgotten, non-Mendelian theory regarding how genes influence human outcomes. We conclude that the field needs to develop models capable of fully incorporating mean effects into twin and adoption studies.

The social origins of obesity within and across generations

We propose a model for obesity development that traces a considerable part of its origins to the social domain (mainly different forms of prolonged social adversity), both within and across generations, working in tandem with a genetic predisposition. To facilitate overview of social pathways, we place particular focus on three areas that form a cascading sequence: (A) social adversity within the family (parents having a low education, a low social position, poverty and financial insecurity; offspring being exposed to gestational stress, unmet social and emotional needs, abuse, maltreatment and other negative life events, social deprivation and relationship discord); (B) increasing levels of insecurity, negative emotions, chronic stress, and a disruption of energy homeostasis; and (C) weight gain and obesity, eliciting further social stress and weight stigma in both generations. Social adversity, when combined with genetic predisposition, thereby substantially contributes to highly effective transmission of obesity from parents to offspring, as well as to obesity development within current generations. Prevention efforts may benefit from mitigating multiple types of social adversity in individuals, families, and communities, notably poverty and financial strain, and by improving education levels.

The "jolly fat" for the middle-aged and older adults in China, was education level considered?

BACKGROUND

Several studies have found a negative association between obesity and depression in Chinese middle-aged and elderly, suggesting the existence of "jolly fat". This study aims to investigate whether "jolly fat" is applicable among middle-aged and elderly with different education levels, and to provide a new perspective for depression screening and obesity interventions in middle-aged and older adults.

METHODS

10,018 individuals aged 45 years and over in China Family Panel Study (2018) were selected for analysis. A short version of Center for Epidemiological Research Depression Scale was used to assess depression. Body mass index was applied to define obesity status. Subgroup analysis of multiple logistic regression was performed to explore whether the relationship between obesity and depression was influenced by education levels.

RESULTS

The prevalence of obesity and depression was 9.02 % and 22.96 % among participants. Obesity reduced the probability of depression in middle-aged and elderly with primary school education or below (OR = 0.71, 95 % CI = 0.56-0.91) while not affecting those with junior high school education or above (OR = 0.80, 95 % CI = 0.57-1.13).

LIMITATIONS

The results cannot be interpreted as causality due to the cross-sectional design. Besides, we cannot directly measure the body composition of the participants.

CONCLUSIONS

"Jolly fat" existed among middle-aged and elderly with low education, but not in those with junior high school education or above. Health care providers need to monitor the psychological status of low-educated middle-aged and older adults who are seen as needing to lose weight, while the underweight group should be the key target of depression screening.

Lifestyle choices mediate the association between educational attainment and BMI in older adults in China: A cross-sectional study

As the Chinese population ages, unhealthfully high body mass index (BMI) levels in older adults are becoming a public health concern as an unhealthfully high BMI is an ill-being condition and can contribute to the risk of disease. Education and lifestyle choices affect BMI; however, the evidence on the relationships and interactions among these factors remains unclear. This study aimed to investigate the mediating effect of lifestyle choices on educational attainment and BMI among older adults in China. Using the Chinese Family Panel Studies (CFPS) 2018 panel data, this study integrated personal- and family-level economic data libraries, including 7,359 adults aged ≥60 years. Lifestyle parameters included smoking amount and screen time. Height and weight values were used to calculate BMI. The chi-square test, binary logistic regression analysis, stepwise regression analysis, and bootstrapping mediating effect tests were used for data analysis. Single-factor chi-square test revealed differences in BMI levels among groups defined by sex, age, residence, marital status, per capita annual household income, education years, and lifestyle choices. Binary logistic regression showed that age, residence, education years, smoking amount, and screen time influenced BMI. Stepwise regression results showed that education years, smoking amount, and screen time were associated with BMI (t = 3.907, -4.902, 7.491, P < 0.001). The lifestyle variables had partial mediating effects on BMI. The mediating effect of lifestyle on BMI was 0.009, while smoking amount was 0.003, and screen time was 0.006. Unhealthfully high BMI levels are increasing among older adults in China and are affected by many factors. Lifestyle factors and educational attainment can interact, affecting BMI. Interventions should consider lifestyle factors and education attainment to help maintain healthy BMI and reduce unhealthfully high BMI incidence.

Financial strain moderates genetic influences on self-rated health: support for diathesis-stress model of gene-environment interplay

Data from the Interplay of Genes and Environment across Multiple Studies (IGEMS) consortium were used to examine predictions of different models of gene-by-environment interaction to understand how genetic variance in self-rated health (SRH) varies at different levels of financial strain. A total of 11,359 individuals from 10 twin studies in Australia, Sweden, and the United States contributed relevant data, including 2,074 monozygotic and 2,623 dizygotic twin pairs. Age ranged from 22 to 98 years, with a mean age of 61.05 (SD = 13.24). A factor model was used to create a harmonized measure of financial strain across studies and items. Twin analyses of genetic and environmental variance for SRH incorporating age, age², sex, and financial strain moderators indicated significant financial strain moderation of genetic influences on self-rated health. Moderation results did not differ across sex or country. Genetic variance for SRH increased as financial strain increased, matching the predictions of the diathesis-stress and social comparison models for components of variance. Under these models, environmental improvements would be expected to reduce genetically based health disparities.

Intergenerational polygenic obesity risk throughout adolescence in a cross-sectional study design: The HUNT study, Norway

OBJECTIVE

This study examined the relationship between parental obesity polygenic risk and children's BMI throughout adolescence. Additionally, from a smaller subsample, the objective was to assess whether parental polygenic risk score (PRS) may act as a proxy for offspring PRS in studies lacking offspring genetic data.

METHODS

A total of 8,561 parent-offspring (age 13-19 years) trios from the Trøndelag Health Study (the HUNT Study) were included, of which, 1,286 adolescents had available genetic data. Weighted parental PRSs from 900 single-nucleotide polymorphisms robustly associated with adult BMI were constructed and applied in linear mixed-effects models.

RESULTS

A positive association between parental PRS and offspring sex- and age-adjusted BMI (iso-BMI) throughout adolescence was identified. The estimated marginal effects per standard deviation increase in parental PRS were 0.26 (95% CI: 0.18-0.33), 0.36 (95% CI: 0.29-0.43), and 0.62 kg/m² (95% CI: 0.51-0.72) for maternal, paternal, and combined parental PRS, respectively. In subsample analyses, the magnitude of association of the parental PRS versus offspring PRS with iso-BMI in adolescents was similar.

CONCLUSIONS

Parental PRS was consistently associated with offspring iso-BMI throughout adolescence. Results from subsample analyses support the use of parental PRS of obesity as a proxy for adolescent PRS in the absence of offspring genetic data.

Obesity and eating behavior from the perspective of twin and genetic research

Obesity has dramatically increased during the last decades and is currently one of the most serious global health problems. We present a hypothesis that obesity is a neuro-behavioral disease having a strong genetic background mediated largely by eating behavior and is sensitive to the macro-environment; we study this hypothesis from the perspective of genetic research. Genetic family and genome-wide-association studies have shown well that body mass index (BMI, kg/m²) is a highly heritable and polygenic trait. New genetic variation of BMI emerges after early childhood. Candidate genes of BMI notably express in brain tissue, supporting that this new variation is related to behavior. Obesogenic environments at both childhood family and societal levels reinforce the genetic susceptibility to obesity. Genetic factors have a clear influence on macro-nutrient intake and appetite-related eating behavior traits. Results on the gene-by-diet interactions in obesity are mixed, but emerging evidence suggests that eating behavior traits partly mediate the effect of genes on BMI. However, more rigorous prospective study designs controlling for measurement bias are still needed.

Neighborhood deprivation index is associated with weight status among long-term survivors of childhood acute lymphoblastic leukemia

PURPOSE

Area deprivation index (ADI), a measure of neighborhood socioeconomic disadvantage, has been linked to metabolic outcomes in the general population but has received limited attention in survivors of childhood acute lymphoblastic leukemia (ALL), a population with high rates of overweight and obesity.

METHODS

We retrospectively reviewed heights and weights of ≥ 5 year survivors of pediatric ALL (diagnosed 1990-2013). Residential addresses were geocoded using ArcGIS to assign quartiles of ADI, a composite of 17 measures of poverty, housing, employment, and education, with higher quartiles reflecting greater deprivation. Odds ratios (OR) and 95% confidence intervals (CI) for the association between ADI quartiles and overweight/obesity or obesity alone were calculated with logistic regression.

RESULTS

On average, participants (n = 454, 50.4% male, 45.2% Hispanic) were age 5.5 years at diagnosis and 17.4 years at follow-up. At follow-up, 26.4% were overweight and 24.4% obese. Compared to the lowest ADI quartile, survivors in the highest quartile were more likely to be overweight/obese at follow-up (OR = 2.33, 95% CI: 1.23-4.44) after adjusting for race/ethnicity, sex, age at diagnosis, and age at follow-up. The highest ADI quartile remained significantly associated with obesity (OR = 5.28, 95% CI: 1.79-15.54) after accounting for weight status at diagnosis.

CONCLUSIONS

This study provides novel insights into possible social determinants of health inequalities among survivors of childhood ALL by reporting a significant association between neighborhood deprivation and overweight/obesity.

IMPLICATIONS FOR CANCER SURVIVORS

Survivors of childhood ALL residing in neighborhood with greater socioeconomic disadvantage may be at increased risk of overweight and obesity and candidates for targeted interventions.

Education, occupation and operational measures of sarcopenia: Six years of Australian data

OBJECTIVES

To examine associations of education and occupation with handgrip strength (HGS), lower limb strength (LLS) and appendicular lean mass (ALM).

METHODS

Measures of HGS, LLS and ALM (dual-energy X-ray absorptiometry) were ascertained at baseline in 1090 adults (50-80 years, 51% women), ~3 and 5 years. Education and occupation were self-reported, the latter categorised as high-skilled white collar (HSWC), low-skilled white collar (LSWC) or blue collar. Separate general estimating equations were performed.

RESULTS

The highest education group had greater HGS than the middle (0.33 psi) and lowest (0.48 psi) education groups, and 0.34 kg greater ALM than the lowest education group. HGS was 0.46 psi greater for HSWC than LSWC groups. Compared to LSWC groups, LLS was 5.38 and 7.08 kg greater in HSWC and blue-collar groups. Blue-collar and HSWC groups each had ~ 0.60-0.80kg greater ALM than LSWC.

CONCLUSION

Progressive muscle loss can be prevented by targeted intervention; thus, we suggest clinical attention be directed towards specific social groups.

Gene-Environment Interplay Between Physical Exercise and Fitness and Depression Symptomatology

Studies often report beneficial effects of physical exercise on depression symptomatology, both in clinical and community samples. In clinical samples, effects are observed using physical exercise as primary treatment and supplement to antidepressant medications and/or psychotherapies. Magnitudes vary with sample characteristics, exercise measure, and study rigor. Both propensity to exercise and vulnerability to depression show genetic influences, suggesting gene–environment interplay. We investigated this in a Danish Twin Registry-based community sample who completed a cycle fitness test and detailed assessments of depression symptomatology and regular exercise engagement that enabled estimates of typical total, intentional exercise-specific, and other metabolic equivalent (MET) expenditures. All exercise-related measures correlated negatively with depression symptomatology (− .07 to − .19). Genetic variance was lower at higher levels of cycle fitness, with genetic and shared environmental correlations of −  .50 and 1.0, respectively. Nonshared environmental variance in depression was lower at higher levels of total MET, with no indications of genetic or environmental covariance. Being physically active and/or fit tended to prevent depression, apparently because fewer participants with higher levels of activity and fitness reported high depression symptomatology. This was driven by nonshared environmental influences on activity but genetic influences on physical fitness. Genetic correlation suggested people less genetically inclined toward physical fitness may also be genetically vulnerable to depression, possibly because inertia impedes activity but also possibly due to social pressures to be fit. Exercise programs for general well-being should emphasize participation, not performance level or fitness. We discuss possible interrelations between fitness aptitude and metabolism.

The moderator effect of age in the association between mood and adiposity in the elderly is specific for the subcutaneous adipose compartment: An MRI study

The positive association between obesity and depressive mood in young- and middle-age individuals is a phenomenon with major clinical implications in public health. Interestingly, the trend of this association in older individuals is not clear, given the conflicting results of multiple studies. Since aging is accompanied by changes in body fat distribution, we questioned whether age is a modulator of such association. This study explores the role of age in the association between mood and general (body mass index [BMI]) and abdominal adiposity (waist circumference [WC]) in older adults characterizing the different abdominal adipose tissue compartments (subcutaneous adipose tissue [SAT] and visceral adipose tissue [VAT]) with magnetic resonance imaging (MRI) techniques.

METHODS

One hundred twenty aged community-dwelling individuals (≥50 y of age) were assessed regarding depressive mood (Geriatric Depression Scale) and adiposity (BMI and WC). From these, 96 were assessed for SAT and VAT using MRI.

RESULTS

Using multiple linear regression models, depressive mood was positively associated with BMI, WC, and VAT. Age was a significant moderator of the association between depressive mood and BMI, WC, and SAT: positive in younger participants and null or negative in older participants. On the other hand, higher VAT was significantly associated with a more depressive mood, independently of age.

CONCLUSIONS

This study identifies age as a relevant moderator in the association between depressive mood and adiposity in the elderlies. Furthermore, the body fat compartment analysis revealed that the effect of age is specific for the SAT, suggesting its protective role in depressive mood.

A genetic sum score of risk alleles associated with body mass index interacts with socioeconomic position in the Heinz Nixdorf Recall Study

Body mass index (BMI) is influenced by genetic, behavioral and environmental factors, while interactions between genetic and socioeconomic factors have been suggested. Aim of the study was to investigate whether socioeconomic position (SEP) interacts with a BMI-related genetic sum score (GRS_BMI) to affect BMI in a population-based cohort. SEP-related health behaviors and a GRS associated with educational attainment (GRS_Edu) were included in the analysis to explore potential interactions underlying the GRS_BMIxSEP effect. Baseline information on SEP indicators (education, income), BMI, smoking, physical activity, alcohol consumption and genetic risk factors were available for 4,493 participants of the Heinz Nixdorf Recall Study. Interaction analysis was based on linear regression as well as on stratified analyses. In SEP-stratified analyses, the highest genetic effects were observed in the lowest educational group with a 0.24 kg/m² higher BMI (95%CI: 0.16; 0.31) and in the lowest income quartile with a 0.14 kg/m² higher BMI (95%CI: 0.09; 0.18) per additional risk allele. Indication for a GRS_BMIxSEP interaction was observed for education (ß_{GRSbmixeducation} = -0.02 [95%CI:-0.03; -0.01]) and income (ß_{GRSbmixincome} = -0.05 [95%CI: -0.08; -0.02]). When adjusting for interactions with the GRS_Edu and SEP-related health behaviors, effect size estimates of the GRS_BMIxSEP interaction remained virtually unchanged. Results gave indication for an interaction of BMI-related genetic risk factors with SEP indicators, showing substantially stronger genetic effects in low SEP groups. This supports the hypothesis that expression of genetic risks is higher in socioeconomically disadvantaged environments. No indication was observed that the GRS_BMIxSEP interaction was affected by other SEP-related factors included in the analysis.

Personality-obesity associations are driven by narrow traits: A meta-analysis

Obesity has inconsistent associations with broad personality domains, possibly because the links pertain to only some facets of these domains. Collating published and unpublished studies (N = 14 848), we meta-analysed the associations between body mass index (BMI) and Five-Factor Model personality domains as well as 30 Five-Factor Model personality facets. At the domain level, BMI had a positive association with Neuroticism and a negative association with Conscientiousness domains. At the facet level, we found associations between BMI and 15 facets from all five personality domains, with only some Neuroticism and Conscientiousness facets among them. Certain personality-BMI associations were moderated by sample properties, such as proportions of women or participants with obesity; these moderation effects were replicated in the individual-level analysis. Finally, facet-based personality "risk" scores accounted for 2.3% of variance in BMI in a separate sample of individuals (N = 3569), 409% more than domain-based scores. Taken together, personality-BMI associations are facet specific, and delineating them may help to explain obesity-related behaviours and inform intervention designs. Preprint and data are available at https://psyarxiv.com/z35vn/.

An examination of multivariable Mendelian randomization in the single-sample and two-sample summary data settings

BACKGROUND

Mendelian randomization (MR) is a powerful tool in epidemiology that can be used to estimate the causal effect of an exposure on an outcome in the presence of unobserved confounding, by utilizing genetic variants that are instrumental variables (IVs) for the exposure. This has been extended to multivariable MR (MVMR) to estimate the effect of two or more exposures on an outcome.

METHODS AND RESULTS

We use simulations and theory to clarify the interpretation of estimated effects in a MVMR analysis under a range of underlying scenarios, where a secondary exposure acts variously as a confounder, a mediator, a pleiotropic pathway and a collider. We then describe how instrument strength and validity can be assessed for an MVMR analysis in the single-sample setting, and develop tests to assess these assumptions in the popular two-sample summary data setting. We illustrate our methods using data from UK Biobank to estimate the effect of education and cognitive ability on body mass index.

CONCLUSION

MVMR analysis consistently estimates the direct causal effect of an exposure, or exposures, of interest and provides a powerful tool for determining causal effects in a wide range of scenarios with either individual- or summary-level data.

Parental Education and Genetics of BMI from Infancy to Old Age: A Pooled Analysis of 29 Twin Cohorts

OBJECTIVE

The objective of this study was to analyze how parental education modifies the genetic and environmental variances of BMI from infancy to old age in three geographic-cultural regions.

METHODS

A pooled sample of 29 cohorts including 143,499 twin individuals with information on parental education and BMI from age 1 to 79 years (299,201 BMI measures) was analyzed by genetic twin modeling.

RESULTS

Until 4 years of age, parental education was not consistently associated with BMI. Thereafter, higher parental education level was associated with lower BMI in males and females. Total and additive genetic variances of BMI were smaller in the offspring of highly educated parents than in those whose parents had low education levels. Especially in North American and Australian children, environmental factors shared by co-twins also contributed to the higher BMI variation in the low education level category. In Europe and East Asia, the associations of parental education with mean BMI and BMI variance were weaker than in North America and Australia.

CONCLUSIONS

Lower parental education level is associated with higher mean BMI and larger genetic variance of BMI after early childhood, especially in the obesogenic macro-environment. The interplay among genetic predisposition, childhood social environment, and macro-social context is important for socioeconomic differences in BMI.

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

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.

Education as a moderator of genetic risk for higher body mass index: prospective cohort study from childhood to adulthood

OBJECTIVES

The life-course development of body mass index (BMI) may be driven by interactions between genes and obesity-inducing social environments. We examined whether lower parental or own education accentuates the genetic risk for higher BMI over the life course, and whether diet and physical activity account for the educational differences in genetic associations with BMI.

SUBJECTS/METHODS

The study comprised 2441 participants (1319 women, 3-18 years at baseline) from the prospective, population-based Cardiovascular Risk in Young Finns Study. BMI (kg/m²) trajectories were calculated from 18 to 49 years, using data from six time points spanning 31 years. A polygenic risk score for BMI was calculated as a weighted sum of risk alleles in 97 single-nucleotide polymorphisms. Education was assessed via self-reports, measured prospectively from participants in adulthood and from parents when participants were children. Diet and physical activity were self-reported in adulthood.

RESULTS

Mean BMI increased from 22.6 to 26.6 kg/m² during the follow-up. In growth curve analyses, the genetic risk score was associated with faster BMI increase over time (b=0.02, (95% CI, 0.01-0.02, P<0.001)). The association between the genetic risk score and BMI was more pronounced among those with lower educational level in adulthood (b=-0.12 (95% CI, -0.23-0.01); P=0.036)). No interaction effect was observed between the genetic risk score and parental education (b=0.05 (95% CI, -0.09-0.18; P=0.51)). Diet and physical activity explained little of the interaction effect between the genetic risk score and adulthood education.

CONCLUSIONS

In this prospective study, the association of a risk score of 97 genetic variants with BMI was stronger among those with low compared with high education. This suggests lower education in adulthood accentuates the risk of higher BMI in people at genetic risk.

Behavioural Susceptibility Theory: Professor Jane Wardle and the Role of Appetite in Genetic Risk of Obesity

PURPOSE OF REVIEW

There is considerable variability in human body weight, despite the ubiquity of the 'obesogenic' environment. Human body weight has a strong genetic basis and it has been hypothesised that genetic susceptibility to the environment explains variation in human body weight, with differences in appetite being implicated as the mediating mechanism; so-called 'behavioural susceptibility theory' (BST), first described by Professor Jane Wardle. This review summarises the evidence for the role of appetite as a mediator of genetic risk of obesity.

RECENT FINDINGS

Variation in appetitive traits is observable from infancy, drives early weight gain and is highly heritable in infancy and childhood. Obesity-related common genetic variants identified through genome-wide association studies show associations with appetitive traits, and appetite mediates part of the observed association between genetic risk and adiposity. Obesity results from an interaction between genetic susceptibility to overeating and exposure to an 'obesogenic' food environment.

Is a Nutrition Education Intervention Associated with a Higher Intake of Fruit and Vegetables and Improved Nutritional Knowledge among Housewives in Mauritius?

The purpose of the study was to assess the determinants of nutrition behaviors and body mass index and determine the impact of a nutrition education intervention (NEI) among Mauritian housewives. A pretest-posttest design was used assessing Nutrition Knowledge (NK), Nutrition Attitudes, Fruit and Vegetable Intake (FVI), body mass index (BMI). Two hundred Mauritian housewives were recruited. The NEI was in the form of a lecture and lasted for twenty minutes. Statistical tests performed revealed that the mean NK score at baseline was 65.8 ± 6.92 and a significant increase of +17.1 at post-test and +16.1 at follow-up was observed. Determinants of NK were age, presence of elderly people, and BMI. Mean nutrition attitude score at baseline was 2.37 ± 0.22 with significant increase of +0.2 (post-test) and +0.17 at follow-up. Age, level of education, presence of elders, and NK were linked to a positive attitude. FVI was predicted by age, income, presence of elders, NK, and nutrition attitudes. Baseline FVI was 4.77 ± 1.11 which increased significantly (p < 0.001) to 4.98 ± 1.13 at post-test and 5.03 ± 1.20 at follow up. NEI had a positive impact suggesting the benefits of such intervention in the promotion of healthy nutrition behaviors.

The interaction between physical activity and obesity gene variants in association with BMI: Does the obesogenic environment matter?

Little is known about how obesity susceptibility single nucleotide polymorphisms (SNPs) interact with moderate to vigorous physical activity (MVPA) in relation to BMI during adolescence, once obesogenic neighborhood factors are accounted for. In race stratified models, including European (EA; N=4977), African (AA; N=1726), and Hispanic Americans (HA; N=1270) from the National Longitudinal Study of Adolescent to Adult Health (1996; ages 12-21), we assessed the evidence for a SNPxMVPA interaction with BMI-for-age Z score, once accounting for obesogenic neighborhood factors including physical activity amenities, transportation and recreation infrastructure, poverty and crime. Eight SNPxMVPA interactions with suggestive significance (p<0.10; three in each EA, and AA, two in HA) were observed showing attenuation on BMI-for-age Z score in adolescents with ≥5 versus <5 bouts/week MVPA, except for rs10146997 (near NRXN3). Findings were robust to the inclusion of neighborhood-level variables as covariates. These findings suggest that any attenuation from MVPA on a genetic susceptibility to obesity during adolescence is likely not operating through obesogenic neighborhood factors.

The genetic architecture of body mass index from infancy to adulthood modified by parental education

OBJECTIVE

A higher prevalence of obesity in lower socioeconomic classes is common in Western societies. This study examined the role of gene-environment interactions in the association between parental education and body mass index (BMI) from infancy to the onset of adulthood.

METHODS

Parentally reported BMI from 1 to 13 and self-reported BMI from 14 to 20 years of age were collected in 16,646 complete Dutch twin pairs and analyzed by genetic twin modeling.

RESULTS

At 7 to 8 years of age, children whose parents had middle or low educational levels had more excess weight than the children of more highly educated parents, and the difference increased until 18 to 20 years of age. The major part of the BMI variation was explained by additive genetic factors (a(2)  = 0.55-0.85), but environmental factors common for co-twins also played a significant role, especially from 3 to 7-8 years of age (c(2)  = 0.15-0.29). The genetic variation in BMI was higher in children whose parents had middle or low educational levels compared with children whose parents had a high educational level.

CONCLUSIONS

The interaction between genetic factors and the childhood social environment may contribute to the formation of socioeconomic differences in obesity.

Maternal overweight/obesity characteristics and child anthropometric status in Jos, Nigeria

Objective:

This study is to determine the pattern of overweight and obesity and its relationship with childhood anthropometric status in Nigeria.

Materials and Methods:

This cross-sectional study was conducted in Jos, Nigeria. Interviewer administered questionnaire was used in data collection. Maternal and child anthropometric measurements were obtained using standard WHO methods. Child anthropometric Z scores were obtained from WHO Anthroplus while BMI of mothers were also determined. Totally, 262 mother-child pairs were recruited.

Results:

Mean maternal age and mean child age were 30.8 ± 6.3 yrs (15-47 yrs) and 22.3 ± 18.7 months (3-72 months). Prevalence of maternal underweight, overweight and obesity was 4.2% (11/262), 29.4% (77/262) and 25.9% (68/262), respectively. Child overweight/obesity was 5.4% (14/262), severe under-nutrition 5.7% (15/262). Mean maternal BMI was higher in the older, more educated and higher socioeconomic status (SES). Child mean birth-weight, weight-for-age Z-score and BMI-for-age Z-score (BAZ) were higher among mothers with BMI ≥ 25 kg/m². All large-for-age babies were in mothers with maternal BMI ≥ 25 kg/m². Childhood over-nutrition was more common in maternal BMI of ≥25 kg/m². Overall, BAZ was directly related with maternal BMI, maternal age and birth-weight, although it was inversely related with maternal BM I ≥ 25 kg/m².

Conclusion:

Higher BMI is seen in educated and higher SES mothers and this impact on childhood anthropometry.

Gene-Environment Interplay in Physical, Psychological, and Cognitive Domains in Mid to Late Adulthood: Is APOE a Variability Gene?

Despite emerging interest in gene-environment interaction (GxE) effects, there is a dearth of studies evaluating its potential relevance apart from specific hypothesized environments and biometrical variance trends. Using a monozygotic within-pair approach, we evaluated evidence of G×E for body mass index (BMI), depressive symptoms, and cognition (verbal, spatial, attention, working memory, perceptual speed) in twin studies from four countries. We also evaluated whether APOE is a 'variability gene' across these measures and whether it partly represents the 'G' in G×E effects. In all three domains, G×E effects were pervasive across country and gender, with small-to-moderate effects. Age-cohort trends were generally stable for BMI and depressive symptoms; however, they were variable-with both increasing and decreasing age-cohort trends-for different cognitive measures. Results also suggested that APOE may represent a 'variability gene' for depressive symptoms and spatial reasoning, but not for BMI or other cognitive measures. Hence, additional genes are salient beyond APOE.

Biometric Modeling of Gene-Environment Interplay: The Intersection of Theory and Method and Applications for Social Inequality

For more than a decade, biometric moderation models have been used to examine whether genetic and environmental influences on individual differences might vary within the population. These quantitative Gene × Environment interaction models have the potential to elucidate not only when genetic and environmental influences on a phenotype might differ, but also why, as they provide an empirical test of several theoretical paradigms that serve as useful heuristics to explain etiology-diathesis-stress, bioecological, differential susceptibility, and social control. In the current article, we review how these developmental theories align with different patterns of findings from statistical models of gene-environment interplay. We then describe the extant empirical evidence, using work by our own research group and others, to lay out genetically informative plausible accounts of how phenotypes related to social inequality-physical health and cognition-might relate to these theoretical models.

Probability and heritability estimates on primary osteoarthritis of the hip leading to total hip arthroplasty: a nationwide population based follow-up study in Danish twins

INTRODUCTION

Primary hip osteoarthritis, radiographic as well as symptomatic, is highly associated with increasing age in both genders. However, little is known about the mechanisms behind this, in particular if this increase is caused by genetic factors. This study examined the risk and heritability of primary osteoarthritis of the hip leading to a total hip arthroplasty, and if this heritability increased with increasing age.

METHODS

In a nationwide population-based follow-up study 118,788 twins from the Danish Twin Register and 90,007 individuals from the Danish Hip Arthroplasty Register for the period 1995 to 2010 were examined. Our main outcomes were the cumulative incidence, proband-wise concordance and heritability on age, within-pair correlations in monozygotic and dizygotic twin pairs, and the genetic and environmental influence estimated in models taking into account that individuals may not have had a total hip arthroplasty at the time of follow-up.

RESULTS

There were 94,063 twins eligible for analyses, comprising 835 cases of 36 concordant and 763 discordant twin pairs. The probability increased particularly from 50 years of age. After sex and age adjustment a significant additive genetic component of 47% (12:79), a shared environmental component of 21% (2:76) and a unique environment component of 32% (21:41) accounted for the variation in population liability to total hip arthroplasty. The sex-adjusted proband-wise concordance and heritability on age indicated an increasing age-associated genetic influence onwards from 60 years of age.

CONCLUSION

The cumulative incidence in primary hip osteoarthritis leading to total hip arthroplasty increases in particular after the age of 50 years in both genders. Family factors of genes and shared environment are highly significant and account for 68% of the variation in the population liability to total hip arthroplasty; however, the genetic influence increases significantly from 60 years of age onwards.

Socioeconomic modifiers of genetic and environmental influences on body mass index in adult twins

OBJECTIVE

Individual measures of socioeconomic status (SES) suppress genetic variance in body mass index (BMI). Our objective was to examine the influence of both individual-level (i.e., educational attainment, household income) and macrolevel (i.e., neighborhood socioeconomic advantage) SES indicators on genetic contributions to BMI.

METHOD

The study used education level data from 4,162 monozygotic (MZ) and 1,900 dizygotic (DZ) same-sex twin pairs (64% female), income level data from 3,498 MZ and 1,534 DZ pairs (65% female), and neighborhood-level socioeconomic deprivation data from 2,327 MZ and 948 DZ pairs (65% female). Covariates included age (M = 40.4 ± 17.5 years), sex, and ethnicity. The cotwin control model was used to evaluate the mechanisms through which SES influences BMI (e.g., through genetic vs. environmental pathways), and a gene-by-environment interaction model was used to test whether residual variance in BMI, after controlling for the main effects of SES, was moderated by socioeconomic measures.

RESULTS

SES significantly predicted BMI. The association was noncausal, however, and instead was driven primarily through a common underlying genetic background that tended to grow less influential as SES increased. After controlling for the main effect of SES, both genetic and nonshared environmental variance decreased with increasing SES.

CONCLUSIONS

The impact of individual and macrolevel SES on BMI extends beyond its main effects. The influence of genes on BMI is moderated by individual and macrolevel measures of SES, such that when SES is higher, genetic factors become less influential.

Behavioral and Environmental Modification of the Genetic Influence on Body Mass Index: A Twin Study

Body mass index (BMI) has a strong genetic basis, with a heritability around 0.75, but is also influenced by numerous behavioral and environmental factors. Aspects of the built environment (e.g., environmental walkability) are hypothesized to influence obesity by directly affecting BMI, by facilitating or inhibiting behaviors such as physical activity that are related to BMI, or by suppressing genetic tendencies toward higher BMI. The present study investigated relative influences of physical activity and walkability on variance in BMI using 5079 same-sex adult twin pairs (70 % monozygotic, 65 % female). High activity and walkability levels independently suppressed genetic variance in BMI. Estimating their effects simultaneously, however, suggested that the walkability effect was mediated by activity. The suppressive effect of activity on variance in BMI was present even with a tendency for low-BMI individuals to select into environments that require higher activity levels. Overall, our results point to community- or macro-level interventions that facilitate individual-level behaviors as a plausible approach to addressing the obesity epidemic among US adults.

Food neophobia associates with lower dietary quality and higher BMI in Finnish adults

OBJECTIVE

Food neophobia has been associated with decreased consumption of vegetables mainly among children. We hypothesized that food neophobia in adults is also associated with lower overall dietary quality and higher BMI.

DESIGN

Data for the present cross-sectional analyses were derived from parents in a follow-up family study.

SETTING

The STEPS study, a longitudinal study of health and development of a cohort of children born in south-west Finland.

SUBJECTS

The parents, 1178 women (age 19-45 years, mean 32·2 years) and 1013 men (age 18-57 years, mean 34·1 years), completed a questionnaire at home when their child was 13 months old. The questionnaire included the Food Neophobia Scale (FNS; range 10-70), the Index of Diet Quality (IDQ; range 0-16) and a measure of fruit and vegetable consumption. At that time the participants' height and weight were also measured by a research nurse to calculate BMI.

RESULTS

Compared with the food neophilics (FNS score 10-24), the food neophobics (FNS score 40-70) consumed fewer vegetables (women: 15 v. 10 portions/week; men: 13 v. 7 portions/week), scored lower on the IDQ (women: 9·7 v. 8·5; men: 8·8 v. 7·8) and had higher BMI (women: 24·2 v. 26·0 kg/m²; men: 26·5 v. 27·5 kg/m²) as tested by one-way ANOVA, with all P values <0·001 in women and <0·05 in men. The food neophobics followed a diet lower in nutritional quality than did the food neophilics, especially regarding vegetables.

CONCLUSIONS

Food neophobia may complicate adaptation to dietary recommendations and predispose to overweight.

Genetic vulnerability to diabetes and obesity: does education offset the risk?

The prevalence of type 2 diabetes (T2D) and obesity has recently increased dramatically. These common diseases are likely to arise from the interaction of multiple genetic, socio-demographic and environmental risk factors. While previous research has found genetic risk and education to be strong predictors of these diseases, few studies to date have examined their joint effects. This study investigates whether education modifies the association between genetic background and risk for type 2 diabetes (T2D) and obesity. Using data from non-Hispanic Whites in the Health and Retirement Study (HRS, n = 8398), we tested whether education modifies genetic risk for obesity and T2D, offsetting genetic effects; whether this effect is larger for individuals who have high risk for other (unobserved) reasons, i.e., at higher quantiles of HbA1c and BMI; and whether effects differ by gender. We measured T2D risk using Hemoglobin A1c (HbA1c) level, and obesity risk using body-mass index (BMI). We constructed separate genetic risk scores (GRS) for obesity and diabetes respectively based on the most current available information on the single nucleotide polymorphism (SNPs) confirmed as genome-wide significant predictors for BMI (29 SNPs) and diabetes risk (39 SNPs). Linear regression models with years of schooling indicate that the effect of genetic risk on HbA1c is smaller among people with more years of schooling and larger among those with less than a high school (HS) degree compared to HS degree-holders. Quantile regression models show that the GRS × education effect systematically increased along the HbA1c outcome distribution; for example the GRS × years of education interaction coefficient was -0.01 (95% CI = -0.03, 0.00) at the 10th percentile compared to -0.03 (95% CI = -0.07, 0.00) at the 90th percentile. These results suggest that education may be an important socioeconomic source of heterogeneity in responses to genetic vulnerability to T2D.

Is the gene-environment interaction paradigm relevant to genome-wide studies? The case of education and body mass index

This study uses data from the Framingham Heart Study to examine the relevance of the gene-environment interaction paradigm for genome-wide association studies (GWAS). We use completed college education as our environmental measure and estimate the interactive effect of genotype and education on body mass index (BMI) using 260,402 single-nucleotide polymorphisms (SNPs). Our results highlight the sensitivity of parameter estimates obtained from GWAS models and the difficulty of framing genome-wide results using the existing gene-environment interaction typology. We argue that SNP-environment interactions across the human genome are not likely to provide consistent evidence regarding genetic influences on health that differ by environment. Nevertheless, genome-wide data contain rich information about individual respondents, and we demonstrate the utility of this type of data. We highlight the fact that GWAS is just one use of genome-wide data, and we encourage demographers to develop methods that incorporate this vast amount of information from respondents into their analyses.

A comparative study of classroom and online distance modes of official vocational education and training

The study discussed in this paper had two principal objectives. The first was to evaluate the distance model of official vocational education and training offered by means of a virtual learning platform. The second was to establish that both on-site classroom and online distance modes of vocational education and training can be seen as complementary in terms of responding to the majority of modern educational needs. We performed a comparative study using data and results gathered over the course of eleven academic years for 1,133 of our students enrolled in an official vocational education and training program, leading to the awarding of a certificate as an Administrative Management Expert. The classes were offered by the Alfonso de Avellaneda Vocational Education and Training School, located in the city of Alcalá de Henares near Madrid, Spain. We offered classes both in traditional classroom mode and through online distance learning. This paper begins with a descriptive analysis of the variables we studied; inferential statistical techniques are subsequently applied in order to study the relationships that help form the basis for the conclusions reached. This study's results provide evidence that a broad offering of vocational education and training opportunities will facilitate access to such learning for students who require it, regardless of their age, employment status, or personal circumstances, with the online distance mode playing a fundamental role while also yielding results equivalent to those observed for classroom instruction.

A dietary restriction influences the progression but not the initiation of MSG-Induced nonalcoholic steatohepatitis

The metabolic syndrome is a major worldwide health care issue and a dominant risk factor for cardiovascular disease. The liver manifestations of this syndrome include nonalcoholic fatty liver disease (NAFLD) and its progressive variant nonalcoholic steatohepatitis (NASH). Although significant research has been performed, the basic pathogenesis of NAFLD/NASH remains controversial and effective treatments are still unavailable. We have previously reported on a murine model of NASH induced by the neonatal injection of monosodium glutamate (MSG), which includes the clinical manifestations of central obesity, diabetes, hyperlipidemia, and ultimately liver inflammation, fibrosis, and cancer. Although MSG is considered a safe food additive, its administration to pregnant rats increases the voracity and growth hormone levels in the offspring. To further understand the biology of this model, we have investigated the influence of the calorie intake on these clinical manifestations by feeding animals a restrictive diet. MSG-treated animals fed a restrictive diet continue to manifest obesity and early stage NASH but have improvements in serum lipid profiles. At 12 months of age, mice had manifestations of obesity, whether animals were fed a restricted or control diet, but animals fed a restrictive diet had a reduction in the progression of NASH. In conclusion, MSG appears to be a critical factor in the initiation of obesity, whereas calorie intake may modulate the progression of disease.

Gene × environment interactions in obesity: the state of the evidence

BACKGROUND/AIMS

Obesity is a pervasive and highly prevalent disease that poses substantial health risks to those it affects. The rapid emergence of obesity as a global epidemic and the patterns and distributions of the condition within and between populations suggest that interactions between inherited biological factors (e.g. genes) and relevant environmental factors (e.g. diet and physical activity) may underlie the current obesity epidemic.

METHODS

We discuss the rationale for the assertion that gene × lifestyle interactions cause obesity, systematically appraise relevant literature, and consider knowledge gaps future studies might seek to bridge.

RESULTS

We identified >200 relevant studies, of which most are relatively small scale and few provide replication data.

CONCLUSION

Although studies on gene × lifestyle interactions in obesity point toward the presence of such interactions, improved data standardization, appropriate pooling of data and resources, innovative study designs, and the application of powerful statistical methods will be required if translatable examples of gene × lifestyle interactions in obesity are to be identified. Future studies, of which most will be observational, should ideally be accompanied by appropriate replication data and, where possible, by analogous findings from experimental settings where clinically relevant traits (e.g. weight regain and weight cycling) are outcomes.

Childhood intelligence and adult obesity

OBJECTIVE

Recent studies conclude childhood intelligence has no direct effect on adult obesity net of education, but evolutionary psychological theories suggest otherwise.

DESIGN AND METHODS

A population (n = 17,419) of British babies has been followed since birth in 1958 in a prospectively longitudinal study. Childhood general intelligence is measured at 7, 11, and 16, and adult BMI and obesity are measured at 51.

RESULTS

Childhood general intelligence has a direct effect on adult BMI, obesity, and weight gain, net of education, earnings, mother's BMI, father's BMI, childhood social class, and sex. More intelligent children grow up to eat more healthy foods and exercise more frequently as adults.

CONCLUSION

Childhood intelligence has a direct effect on adult obesity unmediated by education or earnings. General intelligence decreases BMI only in adulthood when individuals have complete control over what they eat.

Do genetic factors contribute to the relation between education and metabolic risk factors in young adults? A twin study

BACKGROUND

Lower educated people have a higher prevalence of metabolic risk factors (MRF), that is, high waist circumference (WC), high systolic blood pressure, low high-density lipoprotein cholesterol level, high triglycerides and high fasting glucose levels. Behavioural and psychosocial factors cannot fully explain this educational gradient. We aim to examine the possible role of genetic factors by estimating the extent to which education and MRF share a genetic basis and the extent to which the heritability of MRF varies across educational levels.

METHODS

We examined 388 twin pairs, aged 18-34 years, from the Belgian East Flanders Prospective Twin Survey. Using structural equation modelling, a Cholesky bivariate model was applied to assess the shared genetic basis between education and MRF. The heritability of MRF across education levels was estimated using a non-linear multivariate Gaussian regression.

RESULTS

Fifteen percent (P < 0.01) of the negative relation between education and WC was because of genes shared between these two traits. Furthermore, the heritability of WC was lower in the lowest educated group (65%) compared with the highest educated group (78%, P = 0.04). The lower heritabilities among the lower educated twins for the other MRF were not significant. The heritability of glucose was higher in the lowest education (80%) group compared with the high education group (67%, P = 0.01).

CONCLUSION

Our findings suggest that genetic factors partly explain educational differences in WC. Furthermore, the lower heritability estimates in WC in the lower educated young adults suggest opportunities for environmental interventions to prevent the development of full-blown metabolic syndrome in middle and older age.

Is socioeconomic status of the rearing environment causally related to obesity in the offspring?

We attempt to elucidate whether there might be a causal connection between the socioeconomic status (SES) of the rearing environment and obesity in the offspring using data from two large-scale adoption studies: (1) The Copenhagen Adoption Study of Obesity (CASO), and (2) The Survey of Holt Adoptees and Their Families (HOLT). In CASO, the SES of both biological and adoptive parents was known, but all children were adopted. In HOLT, only the SES of the rearing parents was known, but the children could be either biological or adopted. After controlling for relevant covariates (e.g., adoptee age at measurement, adoptee age at transfer, adoptee sex) the raw (unstandardized) regression coefficients for adoptive and biological paternal SES on adoptee body mass index (BMI: kg/m(2)) in CASO were -.22 and -.23, respectively, both statistically significant (p = 0.01). Controlling for parental BMI (both adoptive and biological) reduced the coefficient for biological paternal SES by 44% (p = .034) and the coefficient for adoptive paternal SES by 1%. For HOLT, the regression coefficients for rearing parent SES were -.42 and -.25 for biological and adoptive children, respectively. Controlling for the average BMI of the rearing father and mother (i.e., mid-parental BMI) reduced the SES coefficient by 47% in their biological offspring (p≤.0001), and by 12% in their adoptive offspring (p = .09). Thus, despite the differing structures of the two adoption studies, both suggest that shared genetic diathesis and direct environmental transmission contribute about equally to the association between rearing SES and offspring BMI.

Increasing genetic variance of body mass index during the Swedish obesity epidemic

BACKGROUND AND OBJECTIVES

There is no doubt that the dramatic worldwide increase in obesity prevalence is due to changes in environmental factors. However, twin and family studies suggest that genetic differences are responsible for the major part of the variation in adiposity within populations. Recent studies show that the genetic effects on body mass index (BMI) may be stronger when combined with presumed risk factors for obesity. We tested the hypothesis that the genetic variance of BMI has increased during the obesity epidemic.

METHODS

The data comprised height and weight measurements of 1,474,065 Swedish conscripts at age 18-19 y born between 1951 and 1983. The data were linked to the Swedish Multi-Generation Register and the Swedish Twin Register from which 264,796 full-brother pairs, 1,736 monozygotic (MZ) and 1,961 dizygotic (DZ) twin pairs were identified. The twin pairs were analysed to identify the most parsimonious model for the genetic and environmental contribution to BMI variance. The full-brother pairs were subsequently divided into subgroups by year of birth to investigate trends in the genetic variance of BMI.

RESULTS

The twin analysis showed that BMI variation could be explained by additive genetic and environmental factors not shared by co-twins. On the basis of the analyses of the full-siblings, the additive genetic variance of BMI increased from 4.3 [95% CI 4.04-4.53] to 7.9 [95% CI 7.28-8.54] within the study period, as did the unique environmental variance, which increased from 1.4 [95% CI 1.32-1.48] to 2.0 [95% CI 1.89-2.22]. The BMI heritability increased from 75% to 78.8%.

CONCLUSION

The results confirm the hypothesis that the additive genetic variance of BMI has increased strongly during the obesity epidemic. This suggests that the obesogenic environment has enhanced the influence of adiposity related genes.