A lifecourse mendelian randomization study highlights the long-term influence of childhood body size on later life heart structure

Effects of childhood and adult height on later life cardiovascular disease risk estimated through Mendelian randomization

Taller individuals are at elevated and protected risk of various cardiovascular disease endpoints. Whether this is due to a direct consequence of their height during childhood, a long-term effect of remaining tall throughout the lifecourse, or confounding by other factors, is unknown. We sought to address this by harnessing human genetic data from the UK Biobank to separate the independent effects of childhood and adulthood height using an approach known as lifecourse Mendelian randomization (MR). Protective effects of taller childhood height on risk of later life coronary artery disease (OR = 0.78 per change in height category, 95% CI = 0.70 to 0.86, P = 4 × 10- 10) and stroke (OR = 0.93, 95% CI = 0.86 to 1.00, P = 0.03) using data from large-scale consortia were found using a univariable model, although evidence of these effects attenuated in a multivariable setting upon accounting for adulthood height. In contrast, direct effects of taller childhood height on increased risk of later life atrial fibrillation (OR = 1.61, 95% CI = 1.42 to 1.79, P = 5 × 10- 7) and thoracic aortic aneurysm (OR = 1.55, 95% CI = 1.16 to 1.95, P = 0.03) were found even after accounting for adulthood height. Evidence for both of these direct effects was replicated in the Million Veterans Program. The protective effect of childhood height on risk of coronary artery disease and stroke can be largely explained by taller children typically becoming taller individuals in later life. Conversely, the independent effect of childhood height on increased risk of atrial fibrillation and thoracic aortic aneurysm may point towards developmental mechanisms in early life which confer a lifelong risk on these disease outcomes.

Childhood adiposity underlies numerous adult brain traits commonly attributed to midlife obesity

Obese adults are often reported to have smaller brain volumes than their non-obese peers. Whether this represents evidence of accelerations in obesity-driven atrophy or is instead a legacy of developmental differences established earlier in the lifespan remains unclear. This study investigated whether early-life differences in adiposity explain differences in numerous adult brain traits commonly attributed to mid-life obesity. We used a two-sample life course Mendelian randomization study in 37 501 adults recruited to UK Biobank (UKB) imaging centres from 2014, with secondary analyses in 6996 children assessed in the Adolescent Brain Cognitive Development Study (ABCD) recruited from 2018. Exposures were genetic variants for childhood (266 variants) and adult (470 variants) adiposity derived from a genome-wide association study (GWAS) of 407 741 UKB participants. Primary outcomes were: adult total brain volume; grey matter volume, thickness and surface area; white matter volume and hyperintensities; and hippocampus, amygdala and thalamus volumes at mean age 55 in the UKB. Secondary outcomes were equivalent childhood measures collected at mean age 10 in ABCD. In the UKB, individuals who were genetically predicted to have had higher levels of adiposity in childhood were found to have multiple smaller adult brain volumes relative to intracranial volume [e.g. z-score difference in normalized brain volume per category increase in adiposity-95% confidence interval (CI) = -0.20 (-0.28, -0.12); P = 4 × 10-6]. These effect sizes remained essentially unchanged after accounting for birthweight or current adult obesity in multivariable models, whereas most observed adult effects attenuated towards null [e.g. adult z-score (95% CI) for total volume = 0.06 (-0.05, 0.17); P = 0.3]. Observational analyses in ABCD showed a similar pattern of changes already present in those with a high body mass index by age 10 [z-score (95% CI) = -0.10 (-0.13, -0.07); P = 8 × 10-13], with follow-up genetic risk score analyses providing some evidence for a causal effect already at this early age. Sensitivity analyses revealed that many of these effects were likely due to the persistence of larger head sizes established in those who gained excess weight in childhood [childhood z-score (95% CI) for intracranial volume = 0.14 (0.05, 0.23); P = 0.002], rather than smaller brain sizes per se. Our data suggest that the persistence of early-life developmental differences across the life course may underlie numerous neuroimaging traits commonly attributed to obesity-related atrophy in later life.

Investigating the causal effects of childhood and adulthood adiposity on later life mental health outcome: a Mendelian randomization study

BACKGROUND

Obesity particularly during childhood is considered a global public health crisis and has been linked with later life health consequences including mental health. However, there is lack of causal understanding if childhood body size has a direct effect on mental health or has an indirect effect after accounting for adulthood body size.

METHODS

Two-sample Mendelian randomization (MR) was performed to estimate the total effect and direct effect (accounting for adulthood body size) of childhood body size on anxiety and depression. We used summary statistics from a genome-wide association study (GWAS) of UK Biobank (n = 453,169) and large-scale consortia of anxiety (Million Veteran Program) and depression (Psychiatric Genomics Consortium) (n = 175,163 and n = 173,005, respectively).

RESULTS

Univariable MR did not indicate genetically predicted effects of childhood body size with later life anxiety (beta = - 0.05, 95% CI = - 0.13, 0.02) and depression (OR = 1.06, 95% CI = 0.94, 1.20). However, using multivariable MR, we observed that the higher body size in childhood reduced the risk of later life anxiety (beta = - 0.19, 95% CI = - 0.29, - 0.08) and depression (OR = 0.83, 95% CI = 0.71, 0.97) upon accounting for the effect of adulthood body size. Both univariable and multivariable MR indicated that higher body size in adulthood increased the risk of later life anxiety and depression.

CONCLUSIONS

Higher body size in adulthood may increase the risk of anxiety and depression, independent of childhood higher body size. In contrast, higher childhood body size does not appear to be a risk factor for later life anxiety and depression.

Unravel the distinct effects of adiposity at different life stages on COVID-19 susceptibility and severity: A life-course Mendelian randomization study

Childhood obesity is widely recognized as a risk factor for numerous health conditions, particularly cardiovascular disease. However, it remains unclear whether childhood adiposity directly affects the risk of COVID-19 in later life. We aimed to investigate the causal effects of early life adiposity on COVID-19 susceptibility and severity. We used genetic instruments from large-scale genome-wide association studies to examine the relationships between birth weight, childhood and adulthood adiposity indicators (including body mass index [BMI], obesity, and body size), and COVID-19 outcomes. Univariable and multivariable Mendelian randomization (MR) analyses were used to obtain the causal estimates. Univariable MR analyses found that childhood BMI and obesity were positively associated with COVID-19 risk and severity in adulthood, however, the significant associations were attenuated to null after further adjusting for adulthood adiposity indicators in multivariable MR analyses. In contrast, our analysis revealed strong evidence of a genetically predicted effect of childhood obesity on COVID-19 hospitalization (OR 1.08, 95% CI: 1.01-1.15, p = 2.12E-2), which remained robust even after adjusting for adulthood obesity and potential lifestyle confounders. Our results highlight the importance of promoting healthy weight management throughout life to reduce the risk of COVID-19.

Early-life body mass index and the risk of six cardiovascular diseases: A Mendelian Randomization study

BACKGROUND

Observational studies consistently indicate an association between early-life body mass index (BMI) and several cardiovascular diseases (CVDs). However, the causal relationship remains uncertain. The primary objective of this study was to assess the causal relationship between early-life BMI and six types of CVDs using the Mendelian Randomization (MR) approach.

METHODS

The dataset for this study was derived from large-scale, summary-level Genome-Wide Association Studies. Specifically, the following datasets we used, early-life BMI (n = 61 111, age = 2-10), heart failure (HF) dataset (n = 977 323), atrial fibrillation (AF) dataset (n = 1 030 836), coronary artery disease (CAD) dataset (n = 184 305), peripheral artery disease (PAD) dataset (n = 243 060), deep venous thrombosis (DVT) dataset (n = 1 500 861) and myocardial infarction (MI) dataset (n = 638 000). Multiple MR methods were utilized to evaluate the causal relationship between exposure and outcomes, accompanied by sensitivity analysis.

RESULTS

Early-life BMI positively correlates with the risk of developing the six distinct CVDs included in this study. Specifically, elevated BMI during childhood is associated with a 31.9% risk for HF (Odds ratio [OR] = 1.319, 95% CI [1.160 to 1.499], p = 2.33 × 10-5), an 18.3% risk for AF (R = 1.183, 95% CI [1.088 to 1.287], p = 8.22 × 10-5), an 14.8% risk for CAD (OR = 1.148, 95% CI [1.028 to 1.283], p = 1.47 × 10-2), a 40.5% risk for PAD (OR = 1.405, 95% CI [1.233 to 1.600], p = 3.10 × 10-7) and 12.0% risk for MI (OR = 1.120, 95% CI [1.017 to 1.234], p = 2.18 × 10-2). Interestingly, the risk for deep venous thrombosis only increased by 0.5% (OR = 1.005, 95% CI [1.001 to 1.008], p = 2.13 × 10-3).

CONCLUSION

Genetically inferred early-life BMI is significantly associated with six distinct CVDs. This indicates that elevated early-life BMI is a significant risk factor for multiple cardiovascular disorders.

Evaluating the distinct effects of body mass index at childhood and adulthood on adult major psychiatric disorders

Children with high body mass index (BMI) are at heightened risk of developing health issues in adulthood, yet the causality between childhood BMI and adult psychiatric disorders remains unclear. Using a life course Mendelian randomization (MR) framework, we investigated the causal effects of childhood and adulthood BMI on adult psychiatric disorders, including Alzheimer's disease, anxiety, major depressive disorder, obsessive-compulsive disorder (OCD), and schizophrenia, using data from the Psychiatric Genomics Consortium and FinnGen study. Childhood BMI was significantly associated with an increased risk of schizophrenia, while adulthood BMI was associated with a decreased risk of OCD and schizophrenia. Multivariable MR analyses indicated a direct causal effect of childhood BMI on schizophrenia, independent of adulthood BMI and lifestyle factors. No evidence of causal associations was found between childhood BMI and other psychiatric outcomes. The sensitivity analyses yielded broadly consistent findings. These findings highlight the critical importance of early-life interventions to mitigate the long-term consequences of childhood adiposity.

The Application of Mendelian Randomization in Cardiovascular Disease Risk Prediction: Current Status and Future Prospects

Cardiovascular disease (CVD), a leading cause of death and disability worldwide, and is associated with a wide range of risk factors, and genetically associated conditions. While many CVDs are preventable and early detection alongside treatment can significantly mitigate complication risks, current prediction models for CVDs need enhancements for better accuracy. Mendelian randomization (MR) offers a novel approach for estimating the causal relationship between exposure and outcome by using genetic variation in quasi-experimental data. This method minimizes the impact of confounding variables by leveraging the random allocation of genes during gamete formation, thereby facilitating the integration of new predictors into risk prediction models to refine the accuracy of prediction. In this review, we delve into the theory behind MR, as well as the strengths, applications, and limitations behind this emerging technology. A particular focus will be placed on MR application to CVD, and integration into CVD prediction frameworks. We conclude by discussing the inclusion of various populations and by offering insights into potential areas for future research and refinement.

Methodological approaches, challenges, and opportunities in the application of Mendelian randomisation to lifecourse epidemiology: A systematic literature review

Diseases diagnosed in adulthood may have antecedents throughout (including prenatal) life. Gaining a better understanding of how exposures at different stages in the lifecourse influence health outcomes is key to elucidating the potential benefits of disease prevention strategies. Mendelian randomisation (MR) is increasingly used to estimate causal effects of exposures across the lifecourse on later life outcomes. This systematic literature review explores MR methods used to perform lifecourse investigations and reviews previous work that has utilised MR to elucidate the effects of factors acting at different stages of the lifecourse. We conducted searches in PubMed, Embase, Medline and MedRXiv databases. Thirteen methodological studies were identified. Four studies focused on the impact of time-varying exposures in the interpretation of "standard" MR techniques, five presented methods for repeat measures of the same exposure, and four described methodological approaches to handling multigenerational exposures. A further 127 studies presented the results of an applied research question. Over half of these estimated effects in a single generation and were largely confined to the exploration of questions regarding body composition. The remaining mostly estimated maternal effects. There is a growing body of research focused on the development and application of MR methods to address lifecourse research questions. The underlying assumptions require careful consideration and the interpretation of results rely on select conditions. Whilst we do not advocate for a particular strategy, we encourage practitioners to make informed decisions on how to approach a research question in this field with a solid understanding of the limitations present and how these may be affected by the research question, modelling approach, instrument selection, and data availability.

Characterizing the Causal Pathway From Childhood Adiposity to Right Heart Physiology and Pulmonary Circulation Using Lifecourse Mendelian Randomization

BACKGROUND

Observational epidemiological studies have reported an association between childhood adiposity and altered cardiac morphology and function in later life. However, whether this is due to a direct consequence of being overweight during childhood has been difficult to establish, particularly as accounting for other measures of body composition throughout the lifecourse can be exceptionally challenging.

METHODS AND RESULTS

In this study, we used human genetics to investigate this using a causal inference technique known as lifecourse Mendelian randomization. This approach allowed us to evaluate the effect of childhood body size on 11 measures of right heart and pulmonary circulation independent of other anthropometric traits at various stages in the lifecourse. We found strong evidence that childhood body size has a direct effect on an enlarged right heart structure in later life (eg, right ventricular end-diastolic volume: β=0.24 [95% CI, 0.15-0.33]; P=3×10-7) independent of adulthood body size. In contrast, childhood body size effects on maximum ascending aorta diameter attenuated upon accounting for body size in adulthood, suggesting that this effect is likely attributed to individuals remaining overweight into later life. Effects of childhood body size on pulmonary artery traits and measures of right atrial function became weaker upon accounting for adulthood fat-free mass and childhood height, respectively.

CONCLUSIONS

Our findings suggest that, although childhood body size has a long-term influence on an enlarged heart structure in adulthood, associations with the other structural components of the cardiovascular system and their function may be largely attributed to body composition at other stages in the lifecourse.

Mendelian Randomization as a Tool for Cardiovascular Research: A Review

Importance

Mendelian randomization (MR) is a statistical approach that has become increasingly popular in the field of cardiovascular disease research. It offers a way to infer potentially causal relationships between risk factors and outcomes using observational data, which is particularly important in cases where randomized clinical trials are not feasible or ethical. With the growing availability of large genetic data sets, MR has become a powerful and accessible tool for studying the risk factors for cardiovascular disease.

Observations

MR uses genetic variation associated with modifiable exposures or risk factors to mitigate biases that affect traditional observational study designs. The approach uses genetic variants that are randomly assigned at conception as proxies for exposure to a risk factor, mimicking a randomized clinical trial. By comparing the outcomes of individuals with different genetic variants, researchers may draw causal inferences about the effects of specific risk factors on cardiovascular disease, provided assumptions are met that address (1) the association between each genetic variant and risk factor and (2) the association of the genetic variants with confounders and (3) that the association between each genetic variant and the outcome only occurs through the risk factor. Like other observational designs, MR has limitations, which include weak instruments that are not strongly associated with the exposure of interest, linkage disequilibrium where genetic instruments influence the outcome via correlated rather than direct effects, overestimated genetic associations, and selection and survival biases. In addition, many genetic databases and MR studies primarily include populations genetically similar to European reference populations; improved diversity of participants in these databases and studies is critically needed.

Conclusions and Relevance

This review provides an overview of MR methodology, including assumptions, strengths, and limitations. Several important applications of MR in cardiovascular disease research are highlighted, including the identification of drug targets, evaluation of potential cardiovascular risk factors, as well as emerging methodology. Overall, while MR alone can never prove a causal relationship beyond reasonable doubt, MR offers a rigorous approach for investigating possible causal relationships in observational data and has the potential to transform our understanding of the etiology and treatment of cardiovascular disease.

Time-varying and tissue-dependent effects of adiposity on leptin levels: A Mendelian randomization study

Background

Findings from Mendelian randomization (MR) studies are conventionally interpreted as lifelong effects, which typically do not provide insight into the molecular mechanisms underlying the effect of an exposure on an outcome. In this study, we apply two recently developed MR approaches (known as 'lifecourse' and 'tissue-partitioned' MR) to investigate lifestage-specific effects and tissues of action in the relationship between adiposity and circulating leptin levels.

Methods

Genetic instruments for childhood and adult adiposity were incorporated into a multivariable MR (MVMR) framework to estimate lifestage-specific effects on leptin levels measured during early life (mean age: 10 y) in the Avon Longitudinal Study of Parents and Children and in adulthood (mean age: 55 y) using summary-level data from the deCODE Health study. This was followed by partitioning body mass index (BMI) instruments into those whose effects are putatively mediated by gene expression in either subcutaneous adipose or brain tissues, followed by using MVMR to simultaneously estimate their separate effects on childhood and adult leptin levels.

Results

There was strong evidence that childhood adiposity has a direct effect on leptin levels at age 10 y in the lifecourse (β = 1.10 SD change in leptin levels, 95% CI = 0.90-1.30, p=6 × 10-28), whereas evidence of an indirect effect was found on adulthood leptin along the causal pathway involving adulthood body size (β = 0.74, 95% CI = 0.62-0.86, p=1 × 10-33). Tissue-partitioned MR analyses provided evidence to suggest that BMI exerts its effect on leptin levels during both childhood and adulthood via brain tissue-mediated pathways (β = 0.79, 95% CI = 0.22-1.36, p=6 × 10-3 and β = 0.51, 95% CI = 0.32-0.69, p=1 × 10-7, respectively).

Conclusions

Our findings demonstrate the use of lifecourse MR to disentangle direct and indirect effects of early-life exposures on time-varying complex outcomes. Furthermore, by integrating tissue-specific data, we highlight the etiological importance of appetite regulation in the effect of adiposity on leptin levels.

Funding

This work was supported by the Integrative Epidemiology Unit, which receives funding from the UK Medical Research Council and the University of Bristol (MC_UU_00011/1).

Establishing the relationships between adiposity and reproductive factors: a multivariable Mendelian randomization analysis

BACKGROUND

Few studies have investigated associations between adiposity and reproductive factors using causal methods, both of which have a number of consequences on women's health. Here we assess whether adiposity at different points in the lifecourse affects reproductive factors differently and independently, and the plausibility of the impact of reproductive factors on adiposity.

METHODS

We used genetic data from UK Biobank (273,238 women) and other consortia (EGG, GIANT, ReproGen and SSGAC) for eight reproductive factors: age at menarche, age at menopause, age at first birth, age at last birth, number of births, being parous, age first had sexual intercourse and lifetime number of sexual partners, and two adiposity traits: childhood and adulthood body size. We applied multivariable Mendelian randomization to account for genetic correlation and to estimate the causal effects of childhood and adulthood adiposity, independently of each other, on reproductive factors. Additionally, we estimated the effects of reproductive factors, independently of other relevant reproductive factors, on adulthood adiposity.

RESULTS

We found a higher childhood body size leads to an earlier age at menarche, and an earlier age at menarche leads to a higher adulthood body size. Furthermore, we find contrasting and independent effects of childhood and adulthood body size on age at first birth (beta 0.22 SD (95% confidence interval: 0.14, 0.31) vs - 2.49 (- 2.93, - 2.06) per 1 SD increase), age at last birth (0.13 (0.06,0.21) vs - 1.86 (- 2.23, - 1.48) per 1 SD increase), age at menopause (0.17 (0.09, 0.25) vs - 0.99 (- 1.39, - 0.59) per 1 SD increase), and likelihood of having children (Odds ratio 0.97 (0.95, 1.00) vs 1.20 (1.06, 1.37) per 1 SD increase).

CONCLUSIONS

Our findings demonstrate the importance of considering a lifecourse approach when investigating the inter-relationships between adiposity measures and reproductive events, as well as the use of 'age specific' genetic instruments when evaluating lifecourse hypotheses in a Mendelian randomization framework.

Validation of "Life's Essential 8" Metrics With Cardiovascular Structural Status in Children: The PROC Study in China

Background Life's Essential 8 (LE8) metrics for cardiovascular health (CVH) aid primordial prevention in US populations. Methods and Results We conducted a child cohort study (PROC [Beijing Child Growth and Health Cohort]) with baseline (2018-2019) and follow-up (2020-2021) assessments, enrolling disease-free 6- to 10-year-old children from 6 elementary schools in Beijing. We collected LE8-assessed components via questionnaire surveys and 3 cardiovascular structural parameters by 2-dimensional M-mode echocardiography: left ventricular mass (LVM), LVM index, and carotid intima-media thickness. Compared with 1914 participants (mean age, 6.6 years) at baseline, we saw lower mean CVH scores at follow-up (n=1789; 8.5 years). Among LE8 components, diet presented the lowest perfect-score prevalence (5.1%). Only 18.6% of participants had physical activity ≥420 min/wk, 55.9% had nicotine exposure, and 25.2% had abnormal sleep duration. Prevalence of overweight/obesity was 26.8% at baseline and 38.2% at follow-up. We noted optimal blood lipid scores in 30.7%, while 12.9% of children had abnormal fasting glucose. Normal BP was 71.6% at baseline and 60.3% at follow-up. LVM (g), LVM index (g/m2.7), and carotid intima-media thickness (mm) were significantly lower in children with high (56.8, 33.2, 0.35) or moderate CVH scores (60.6, 34.6, 0.36), compared with children with low CVH scores (67.9, 37.1, 0.37). Adjusting for age/sex, LVM (β=11.8 [95% CI, 3.5-20.0]; P=0.005), LVM index (β=4.4 [95% CI, 0.5-8.3]; P=0.027), and carotid intima-media thickness (β=0.016 [95% CI, 0.002-0.030]; P=0.028) were higher in the low-CVH group. Conclusions CVH scores were suboptimal, declining with age. LE8 metrics indicated worse CVH in children with abnormal cardiovascular structural measurements, suggesting the validity of LE8 in assessing child CVH. Registration URL: https://www.chictr.org.cn/index.html; Unique identifier: ChiCTR2100044027.

Adiposity may confound the association between vitamin D and disease risk - a lifecourse Mendelian randomization study

Background

Vitamin D supplements are widely prescribed to help reduce disease risk. However, this strategy is based on findings using conventional epidemiological methods which are prone to confounding and reverse causation.

Methods

In this short report, we leveraged genetic variants which differentially influence body size during childhood and adulthood within a multivariable Mendelian randomization (MR) framework, allowing us to separate the genetically predicted effects of adiposity at these two timepoints in the lifecourse.

Results

Using data from the Avon Longitudinal Study of Parents and Children (ALSPAC), there was strong evidence that higher childhood body size has a direct effect on lower vitamin D levels in early life (mean age: 9.9 years, range = 8.9-11.5 years) after accounting for the effect of the adult body size genetic score (beta = -0.32, 95% CI = -0.54 to -0.10, p=0.004). Conversely, we found evidence that the effect of childhood body size on vitamin D levels in midlife (mean age: 56.5 years, range = 40-69 years) is putatively mediated along the causal pathway involving adulthood adiposity (beta = -0.17, 95% CI = -0.21 to -0.13, p=4.6 × 10-17).

Conclusions

Our findings have important implications in terms of the causal influence of vitamin D deficiency on disease risk. Furthermore, they serve as a compelling proof of concept that the timepoints across the lifecourse at which exposures and outcomes are measured can meaningfully impact overall conclusions drawn by MR studies.

Funding

This work was supported by the Integrative Epidemiology Unit which receives funding from the UK Medical Research Council and the University of Bristol (MC_UU_00011/1).