Grandparental education, parental education and child height: evidence from Hong Kong's "Children of 1997" birth cohort

Exposure to Chinese famine in early life and height across 2 generations: a longitudinal study based on the China Health and Nutrition Survey

BACKGROUND

Poor nutrition early in life is associated with short stature, which is associated with increased risk of cardiovascular disease and mortality in later life. Less evidence is available about the impact of early-life nutrition on height growth in the subsequent generation.

OBJECTIVES

This study investigated the associations of famine exposure in utero and early childhood with height across 2 generations.

METHODS

We used longitudinal data from the China Health and Nutrition Survey. We included 5401 participants (F1) born in 1955-1966 (calendar year around the Chinese famine in 1959-1961) and their 3930 biological offspring (F2). We classified F1 participants into subgroups by famine exposure status (unexposed/exposed) and timing (fetal-/childhood-exposed) according to their birth year and grouped F2 by their parents' exposure. Linear regression models were applied to examine the associations of famine exposure with adult height of F1 and F2. Linear mixed effect models with fractional polynomial functions were performed to estimate the difference in height between exposure groups of F2 during childhood.

RESULTS

Participants (F1) exposed to famine in utero or in childhood were shorter than those unexposed by 0.41 cm (95% CI: 0.03, 0.80) and 1.12 cm (95% CI: 0.75, 1.48), respectively. Offspring (F2) of exposed fathers were also shorter than those of unexposed parents by 1.07 cm (95% CI: 0.28, 1.86) during childhood (<18 y) and by 1.25 cm (95% CI: 0.07, 2.43) in adulthood (≥18 y), and those with exposed parents had a reduced height during childhood by 1.29 cm (95% CI: 0.68, 1.89) (all P values < 0.05). The associations were more pronounced among child offspring of highly-educated F1, particularly for paternal exposure and among female offspring (all P for interaction < 0.05).

CONCLUSIONS

The findings support the intergenerational associations of famine exposure in early life with height in Chinese populations, indicating the public health significance of improving the nutritional status of mothers and children in the long run.

Short stature is associated with low flow-mediated vasodilation in Japanese men

An inverse association between height and the risk of cardiovascular disease has been reported. The objective of this study was to examine the association between height and endothelial function assessed by flow-mediated vasodilation (FMD). We evaluated cross-sectional associations of height with FMD in 7682 Japanese men. All participants were divided into four groups based on height: <155.0 cm, 155.0-164.9 cm, 165.0-174.9 cm, and ≥175.0 cm. Subjects in a lower quartile of FMD were defined as subjects having low FMD values. Univariate regression analysis revealed that height was significantly correlated with FMD (r = 0.14, p < 0.001). FMD values were 4.6 ± 3.1% in the <155.0 cm group, 5.2 ± 3.1% in the 155.0-164.9 cm group, 5.7 ± 3.1% in the 165.0-174.9 cm group and 6.1 ± 3.2% in the ≥175.0 cm group. FMD significantly increased in relation to an increase in height. Multiple logistic regression analysis revealed that higher height groups were significantly associated with a decreased risk of low FMD value compared with the <155.0 cm group after adjustments for age, presence of hypertension, dyslipidemia, diabetes, current smoking, and brachial artery diameter. FMD was low in subjects with a short stature compared with that in subjects with tall stature. Individuals with a short stature may require intensive interventions to reduce the risk of cardiovascular events.Clinical Trial Registration Information: URL for Clinical Trials: http://www.umin.ac.jp Registration Number for Clinical Trials: UMIN000012952.

The Impact of Early-Life Exposures on Women's Reproductive Health in Adulthood

Purpose of Review

To review the effects of early-life, preconception, and prior-generation exposures on reproductive health in women.

Recent Findings

Women’s early-life factors can affect reproductive health by contributing to health status or exposure level on entering pregnancy. Alternately, they can have permanent effects, regardless of later-life experience. Nutrition, social class, parental smoking, other adverse childhood experiences, environmental pollutants, infectious agents, and racism and discrimination all affect reproductive health, even if experienced in childhood or in utero. Possible transgenerational effects are now being investigated through three- or more-generation studies. These effects occur with mechanisms that may include direct exposure, behavioral, endocrine, inflammatory, and epigenetic pathways.

Summary

Pregnancy is increasingly understood in a life course perspective, but rigorously testing hypotheses on early-life effects is still difficult. In order to improve the health outcomes of all women, we need to expand our toolkit of methods and theory.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40471-021-00279-0.

Methodological Issues in Population-Based Studies of Multigenerational Associations

Laboratory-based animal research has revealed a number of exposures with multigenerational effects-ones that affect the children and grandchildren of those directly exposed. An important task for epidemiology is to investigate these relationships in human populations. Without the relative control achieved in laboratory settings, however, population-based studies of multigenerational associations have had to use a broader range of study designs. Current strategies to obtain multigenerational data include exploiting birth registries and existing cohort studies, ascertaining exposures within them, and measuring outcomes across multiple generations. In this paper, we describe the methodological challenges inherent to multigenerational studies in human populations. After outlining standard taxonomy to facilitate discussion of study designs and target exposure associations, we highlight the methodological issues, focusing on the interplay between study design, analysis strategy, and the fact that outcomes may be related to family size. In a simulation study, we show that different multigenerational designs lead to estimates of different exposure associations with distinct scientific interpretations. Nevertheless, target associations can be recovered by incorporating (possibly) auxiliary information, and we provide insights into choosing an appropriate target association. Finally, we identify areas requiring further methodological development.

Genetic and environmental influences on human height from infancy through adulthood at different levels of parental education

Genetic factors explain a major proportion of human height variation, but differences in mean stature have also been found between socio-economic categories suggesting a possible effect of environment. By utilizing a classical twin design which allows decomposing the variation of height into genetic and environmental components, we tested the hypothesis that environmental variation in height is greater in offspring of lower educated parents. Twin data from 29 cohorts including 65,978 complete twin pairs with information on height at ages 1 to 69 years and on parental education were pooled allowing the analyses at different ages and in three geographic-cultural regions (Europe, North America and Australia, and East Asia). Parental education mostly showed a positive association with offspring height, with significant associations in mid-childhood and from adolescence onwards. In variance decomposition modeling, the genetic and environmental variance components of height did not show a consistent relation to parental education. A random-effects meta-regression analysis of the aggregate-level data showed a trend towards greater shared environmental variation of height in low parental education families. In conclusion, in our very large dataset from twin cohorts around the globe, these results provide only weak evidence for the study hypothesis.

Predictors of adults' body mass index and the association with index child's infant birth weight, in the Lifeways Cross-Generation Cohort Study of a thousand families in the Republic of Ireland

The Lifeways study is novel in having information on three generations of the same families. It is well established that infant birth weight (IBW) predicts individuals' risk of adult chronic disease and more recently studies report cross-generation transmission of risk patterns. The aims of this analysis were to examine whether adults' birth weights were associated with measures of own health status or social position and to relate adults' birth weights to that of the index child's IBW. Finally, we assessed whether birth weight of either adults or children was associated with adult body mass index (BMI) of parents and grandparents. We included 1075 children whose IBW was recorded at recruitment from hospital records and 2546 adult cohort members followed from 2001 until 2014. At baseline, a sub-group of 920 adults had reported own birth weight (RBW). Results showed male adults' RBW were significantly higher than females' (P=0.001). Mothers' RBW was significantly correlated with IBW (r=0.178, P<0.001). In mixed effects linear models with BMI as the outcome variable, of all adults, and in sub-groups of adults with RBW and of mothers only, the IBW was associated with adult BMI adjusting for other predictors. Adults' BMI was positively associated with age (P=0.013), index child's IBW (P=0.001), gender (P<0.001) but not own RBW, adjusting for family identification number. When mothers were removed from the adult models however, IBW ceased to be associated with BMI, a final model showed RBW being associated with adult BMI (P=0.04). There are cross-generational associations in the Lifeways cohort, the maternal association being stronger.

Spillovers between siblings and from offspring to parents are understudied: A review and future directions for research

BACKGROUND

While a large literature has highlighted the protective effects of human capital on an individual's health and to some extent their offspring's health, little evidence is available on the positive spillover benefits of human capital for other family members. We conducted a scoping review of the evidence and identify future directions for research.

METHODS

We systematically searched the public health and economics literature on spillover effects from human capital, as indicated by educational attainment, to the health and/or survival of family members. We assessed (i) downward spillover effects (from parents and/or grandparents to offspring), (ii) horizontal spillover effects (from partners, spouses, and/or siblings), and (iii) upward spillover effects (from offspring to their parents and/or grandparents). We assessed the frequency of studies, their study designs, findings, and identified priority areas to inform future research on spillover effects of human capital.

FINDINGS

A total of 567 studies met our selection criteria. 286 studies assessed downward spillovers, 22 studies assessed horizontal spillovers, and five studies assessed upward spillovers. Studies on horizontal and upward spillovers found universally positive associations between additional education and better health in family members. The majority of studies used cross-sectional and longitudinal study designs as opposed to (quasi-)experimental designs. Further research is needed on horizontal and upward spillovers and research in low-resource settings, in addition to understanding what level of education matters the most, as well as mechanisms.

CONCLUSIONS

Although positive spillovers of human capital between siblings and from offspring to parents are likely, they have been understudied. Estimates of the returns to human capital that exclude these benefits may be too low.

Grandparental education, parental education and adolescent blood pressure

BACKGROUND

Maternal and paternal education could affect childhood blood pressure differently. Grandparental education might also play a role. Disentangling their contribution to childhood blood pressure may shed light on the persistence of disparities and potential windows of intervention.

METHODS

Using 5604 participants from a Chinese birth cohort born in 1997 and followed-up until ~13years (68% of follow-up), we examined the associations of parental education and grandparental education with age-, sex, and height-specific blood pressure z-scores or prehypertension status.

RESULTS

Parental education was inversely associated with adolescent systolic (-0.11 z-score, equivalent to -1.17mmHg, 95% confidence interval (CI) -0.19 to -0.04 for grade ≥12 compared with grade ≤9) and diastolic blood pressure (-0.07 z-score, equivalent to -0.79mmHg, 95% CI -0.11 to -0.04). The magnitude of association was similar for maternal or paternal education. Grandparental education was not associated with adolescent blood pressure. No association with prehypertension was found.

CONCLUSIONS

In an economically developed non-Western setting, both maternal and paternal, but not grandparental, education was associated with adolescent blood pressure. Blood pressure may be responsive to contemporary family socioeconomic conditions that may be scrutinized for suitable interventions.

Associations of Birth Order with Early Adolescent Growth, Pubertal Onset, Blood Pressure and Size: Evidence from Hong Kong's "Children of 1997" Birth Cohort

Background

Birth order has been proposed as a cardiovascular risk factor, because the lower birth weight and greater infant weight gain typical of firstborns could programme metabolism detrimentally.

Methods

We examined the associations of birth order (firstborn or laterborn) with birth weight-for-gestational age, length/height and body mass index (BMI) z-scores during infancy, childhood, and puberty using generalized estimating equations, with age at pubertal onset using interval-censored regression and with age-, sex- and height-standardized blood pressure, height and BMI z-scores at 13 years using linear regression in a population-representative Chinese birth cohort: “Children of 1997” (n = 8,327).

Results

Compared with laterborns, firstborns had lower birth weight-for-gestational age (mean difference = -0.18 z-score, 95% confidence interval (CI) -0.23, -0.14), lower infant BMI (-0.09 z-score, 95% CI -0.14, -0.04), greater childhood height (0.10 z-score, 95% CI 0.05, 0.14) and BMI (0.08 z-score, 95% CI 0.03, 0.14), but not greater pubertal BMI (0.05 z-score, 95% CI -0.02, 0.11), adjusted for sex, parental age, birthplace, education and income. Firstborns had earlier onset of pubic hair (time ratio = 0.988, 95% CI 0.980, 0.996), but not breast or genitalia, development. Firstborns had greater BMI (0.07 z-score, 95% CI 0.002, 0.15), but not height (0.05 z-score, 95% CI -0.01, 0.11), at 13 years, but similar blood pressure.

Conclusions

Differences by birth order continue into early adolescence with firstborns being heavier with earlier pubic hair development, which could indicate long-term cardiovascular risk.

Invited Commentary: Multigenerational Social Determinants of Health—Opportunities and Challenges

An emerging area of social epidemiology examines the relationship between grandparental education and grandchild health. In an accompanying article, Huang et al. (Am J Epidemiol. 2015;182(7):568-578) join the small but growing body of research on this topic. It is useful to contextualize Huang et al.'s work within the much larger body of research examining relationships between education and health within a single generation or across 2 generations. These investigators have generally concluded that higher educational attainment is robustly associated with better health. There are many potential mechanisms through which education and other social exposures may affect health outcomes in a single generation or across generations, and estimating direct and indirect effects can be helpful for assessing specific mechanisms. Researchers conducting multigenerational analyses are faced with several challenges, including limited availability of data for some measures (e.g., educational attainment, and sometimes for 1 grandparent only), limited age ranges of participants, disparate social and political contexts in which study participants of different generations have lived, and patterns of social class reproduction. We encourage future researchers to weave together the careful analytical considerations illustrated by Huang et al. with a rich understanding of the social context for each of the generations studied to help overcome these challenges and advance our understanding of multigenerational social determinants of health.

Are Early-Life Socioeconomic Conditions Directly Related to Birth Outcomes? Grandmaternal Education, Grandchild Birth Weight, and Associated Bias Analyses

Grandmaternal education may be related to grandchild birth weight (GBW) through maternal early-life development; however, conventional regression models may be endogenously confounded. Alternative models employing explicit structural assumptions may provide incrementally clearer evidence. We used data from the US National Longitudinal Study of Adolescent to Adult Health (1995-2009; 1,681 mother-child pairs) to estimate "direct effects" of grandmaternal educational level (less than high school, high school diploma or equivalent, or college degree) at the time of the mother's birth on GBW, adjusted for maternal life-course factors: maltreatment as a child, education and income as an adult, prepregnancy overweight, and prenatal smoking. Using conventional and marginal structural model (MSM) approaches, we estimated 54-g (95% confidence interval: -14.0, 122.1) and 87-g (95% confidence interval: 10.9, 162.5) higher GBWs per increase in educational level, respectively. The MSM allowed simultaneous mediation by and adjustment for prepregnancy overweight. Estimates were insensitive to alternate structural assumptions and mediator parameterizations. Bias analysis suggested that a single unmeasured confounder would have to have a strong influence on GBW (approximately 150 g) or be greatly imbalanced across exposure groups (approximately 25%) to completely explain the findings. Coupling an MSM with sensitivity analyses provides some evidence that maternal early-life socioeconomic environment is directly associated with offspring birth weight.

Body mass index is associated with the maternal lines but height is heritable across family lines in the Lifeways Cross-Generation Cohort Study

OBJECTIVES

Overweight and obesity is a problem in children in particular and determining pathways of transmission is important in prevention. We aimed to examine associations for body mass index (BMI) across three generations of the same families.

PARTICIPANTS

Members of 556 families in the Lifeways Cross-Generation Cohort Study 2001-2014.

SETTING

Community-based study with linkage to health records in the Republic of Ireland.

METHODS

Employing a novel mixed-method approach which adjusts for age and familial group, BMI correlations were estimated at three ages of the index child, that is, at birth and at ages 5 and 9. Height was also examined for comparative purposes.

RESULTS

Correlation of offspring's BMI with that of the mother increased with age (correlation coefficient 0.15 increasing to 0.28, p value <0.001 in all cases) while no consistent pattern was seen with offspring and fathers. There was an association also with each parent and their own mother. Offspring's BMI was correlated to a lesser extent with that of the maternal grandmother while for girls only there was an association with that of the paternal grandmother at ages 0 and 5 (correlation coefficients 0.25, 0.28, p values 0.02, 0.01, respectively). In contrast, height of the child was strongly associated with those of all family members at age 5, but at birth and at age 9 only there was an association with those of the parents and the paternal grandfather. Correlation of offspring's height with those of the mother and father increased with age.

CONCLUSIONS

The results suggest that BMI is predominantly associated with the maternal line, possibly either with intrauterine development, or inherited through the X chromosome, or both, while height is a more complex trait with genetic influences of the parents and that of the paternal grandfather predominating.