Here we present age and sex differences, describing the distribution of detailed/NMR-based metabolite measures in Australian 11–12-year-old children and their parents, and demonstrate that many metabolite measures have moderate parent-child concordance and in general there is a high level of agreement in the magnitude of concordance across metabolites. In accord with previous studies, we observed major differences in metabolite levels between childhood and adulthood and also differences by sex in both childhood and adulthood. We also observed variability in the magnitude of differences by sex for several metabolites in childhood compared with adulthood and identified a complex interplay of correlations of specific metabolites between parents and their children according to parent–child sex relationships.
This is the first major cohort study to report both sex and cross-generational differences in metabolomic concentrations in mid-childhood to adulthood utilising the NMR platform. Further strengths include a large number of parent–child dyads representing a wide range of parent ages, the national population-based sample and the state-of-the-art measurements. Replication studies exploring sex differences in earlier and later stages of childhood and adolescence would strengthen findings.
An important limitation is that paternal factors were not fully represented, as most parental samples were from mothers (a well-documented problem in longitudinal cohort studies). This also limited sex-specific parental contribution analysis; further studies including more fathers are warranted. Additional limitations are that, without samples from both parents for each child, we could not estimate heritability, and our results might not apply to mid-life adults who are not parents (although we see no good reason why these would differ greatly). The original uptake of just over 50% and subsequent attrition within LSAC and then the CheckPoint have led to a relatively advantaged sample, but nonetheless, participants varied widely on key potential confounders (eg, disadvantage and age) and this was at least partly offset by application or consideration of survey weights. Given a large number of metabolites and modest sample size, considerable uncertainty remains in any ranking of the various effects across metabolites. In addition, given the descriptive aims of the paper, additional factors and potential confounders not considered could explain some of the results observed.
Overall, we found a difference in metabolite profile between children and their parents. This was apparent for specific metabolite measures (such as some amino acids) as well as the distribution of metabolites (such as lipid composition of lipoproteins of different density). Some measures were higher in adults, some similar, while a minority were lower. Previous studies, largely in adults, have identified a range of specific metabolite changes with age, particularly from mid to late adulthood.27 This includes a general decrease in several amino acid species, which contrasts with our findings from childhood to mid-adulthood.8 Only the amino acid glutamine showed this pattern in our dataset.
Differences in children by sex (±0.2 SD) were generally much smaller than in adults (±0.8 SD). Large metabolomic studies using alternative platforms have previously reported reproducible, sex-specific signatures in circulating metabolite profile in adults.28 29 This includes differences in amino acid and lipid serum concentrations, potentially influenced by sex-specific effects of genetic polymorphisms on metabolite levels.29 30 As in our study, most amino acids have usually been reported to be higher in men than women.29 31 For example, in a recent study of 507 metabolic markers in 1756 individuals (903 women and 853 men aged ~60 years), one third of metabolites showed significant sexual dimorphism. These were predominantly related to pathways of steroid metabolism, fatty acids, other lipids and a large proportion of amino acids.31 Of particular note, branched chain amino acids (BCAAs) and their related metabolic products were among the most differentially represented, with much higher isoleucine, leucine and valine in men. A similar finding of higher leucine and valine was also noted in the Cooperative Health Research in the Region of Augsburg (KORA) follow-ups 3 (F3) and 4 (F4) analysis of >3000 adults,29 consistent with our observations in adulthood.
In children, we found that sex differences for leucine and valine were smaller but in the same direction as adults. Several lines of evidence implicate BCAA metabolism with metabolic risk in humans. For example, three candidate genes for obesity and/or type 2 diabetes mellitus (T2DM) are involved in the BCAA metabolic pathway.32 In a recent large meta-analysis of metabolomics in diabetes, a >30% higher risk of T2D was found per SD increase in isoleucine, leucine, valine or tyrosine, whereas glycine and glutamine were inversely associated with risk.32 Several clinical studies have also reported that BCAAs positively correlate with insulin resistance, homeostatic model assessment index and levels of haemoglobin A1c, while longitudinal studies have reported that increased blood BCAAs are predictive of future insulin resistance and T2D.33 It is intriguing to speculate that the higher BCAA in males from early life could contribute to the well-described increasing prevalence of T2D in men. Levels of BCAA are elevated in women with polycystic ovary syndrome, potentially contributing to the associated insulin resistance.34 However, it remains unclear whether BCAAs are on the causal pathway to T2D or result from adverse metabolic health. Our demonstration that the sex differences in BCAA possibly arise early in life offers potential to track their association with sex-specific measures of metabolic health from an early age to help clarify where they lie on the causal pathway.
In accord with previous adult studies,29 we found higher levels of glycine in mothers than fathers, and (less markedly) in girls than boys. Interestingly, recent metabolomics and genetic analyses of ~10 000 adults with cardiovascular disease (CVD), with replication in >53 000 subjects, identified a genetic variant in carbamoyl-phosphate synthetase 1 (CPS1) (linked to plasma glycine levels) to be strongly associated with a reduced risk of CVD in women (p=6.3×10−5) but not men (p=0.95), suggesting a direct link between glycine levels and CVD risk, although whether this is a causal association remains unclear.35 It will be interesting in the future to explore the link between variants in CPS1 and circulating glycine levels from early life to adulthood in relation to markers of cardiovascular health in females.
The small sex differences of HDL cholesterol and ApoA-1 in children compared with adults is consistent with modest differences in children, whereas substantial differences in adulthood have previously been reported.36 ApoA-1 was more abundant in boys, whereas ApoB was higher in girls, leading to a higher ApoB/ApoA-1 ratio in girls. The opposite pattern was found in our limited sample of fathers relative to mothers. These data are surprising and differ from a similarly sized study of slightly older European adolescent children (mean age 15 years) that found higher ApoA-1 and ApoB in girls relative to boys.37 Interestingly, a higher ApoB/ApoA-1 ratio has been strongly linked to increased coronary risk in adults,38–40 suggesting that sex differences may alter with increasing age, in keeping with the increased CVD risk in adult men. ApoA-1 is the main protein component of HDL cholesterol41 thus the differences in trajectories in lipids and HDL cholesterol for boys and girls across childhood that have been reported42 43 could partially explain this observation.
These are the first data on the mother–child or parent–child correlations of NMR metabolites. Smaller studies have reported positive correlations between parents and children for a limited range of cardiometabolic risk factors including total cholesterol, LDL cholesterol, HDL cholesterol and triglycerides measured using conventional methods. We found positive correlations between parents and children for the same lipid measures (although measured using NMR) consistent with previously reported findings. One study reported a positive association between the serum lipid levels of 4-year-old children (n=127) and their parents (122 mothers and 118 fathers)44 whereas another study of children aged 6–18 years (n=255) and their parents (n=179) found that the age of the child influenced the degree of correlation of several lipid measures, with older (10–18 years) children more similar to their parents in terms of triglyceride levels than younger individuals (6–9 years).12
The temporal and sex-specific dynamism of the metabolomics data we describe here offer considerable opportunities for identification of biomarkers of risk for a range of non-communicable diseases early in life to inform targeted interventions and monitor their efficacy. Combining metabolomics with other ‘omics data (such as genetics), as is increasingly reported from large adult studies, offers considerable promise in understanding the causal pathways that link early life exposures, genetics and intermediate phenotypes with later onset chronic disease and in identifying clinically relevant biomarkers.
In conclusion, we describe the metabolite profile from mid-childhood and adulthood in a population-based sample, together with parent–child concordance and differences by sex in children and adults. In this descriptive paper, distinct differences in profiles were observed by age and sex, as well as considerable evidence of a correlation between parent and child measures. These data will be informative for investigation of the childhood origins of adult non-communicable diseases and for comparative studies across populations.
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