Abstract
Background
Parent-child separation is a risk factor for children’s physical and mental problems, limited literature has explored the impact on children’s development across generations. Here, we examine the effects of intergenerational parent-child separation on accelerating biological aging in preschool children, as indicated by the accelerated eruption of the first permanent molar (M1) and oral epithelial cell telomere length (TL).
Methods
This study draws on data from a child growth cohort established in rural areas of Anhui Province, China, which included 2,367 children aged 3–6 years. Researchers collected data on parent-child separation experiences and demographic characteristics of both parents and offspring, followed by comprehensive physical and oral examination. Parent-child separation during the parents’ childhood and their children’s separation experiences were recognized as distinct generational exposures, while intergenerational continuity of parent-child separation was defined as both generations experiencing separation. During dental examinations, M1 eruption was classified as accelerated if occurring before 6.1 years in girls or 6.3 years in boys. A follow-up oral examination was conducted six months later, with oral epithelial samples collected for TL measurement.
Results
Children with missing data, deciduous dentition or undetermined M1 eruption status were excluded, yielding a final sample of 895 children (mean [SD] age: 6.01 [0.14] years). Among these, 179 (20%) experienced intergenerational continuity of parent-child separation. The included children with a mean (SD) age of 6.01 (0.14) years. The overall prevalence of accelerated M1 eruption was 28.7% (257/895). Children exposed to intergenerational continuity of parent-child separation showed a 2.03-times increased risk of accelerated M1 eruption (95% CI: 1.24–3.33, p = 0.005), and 23% shorter telomeres (95% CI: -0.32 to -0.14, p < 0.001) compared to unexposed children. Sensitivity analyses revealed that both paternal and maternal transmission contributed to accelerated biological aging in the oral cavity, though paternal transmission showed stronger effects.
Conclusion
Our findings demonstrate that intergenerational parent-child separation adversely impacts biological aging in the oral cavity of preschool children. These results underscore the critical need to break the intergenerational cycle of parent-child separation in children’s oral health and overall health.
Graphical abstract
Supplementary Information
The online version contains supplementary material available at 10.1186/s12903-026-07865-y.
Keywords: Preschool children, Parent-child separation, Intergenerational continuity, First molar, Telomere length, Biological aging
Introduction
With the accelerated economic growth and urbanization in China, an increasing number of people tend to migrate to urban or metropolitan areas for broader opportunities. However, due to the restrictive household registration policies in China, as well as the exorbitant living and schooling costs in metropolis, most migrant workers were forced to leave their children behind in rural areas. Decades later, these children who have been forcibly separated from their parents have grown up and become parents themselves, often raising their own offspring under comparable circumstances [1], perpetuating an intergenerational cycle of parent-child separation. Official data reveal that approximately 69 million children in rural China—representing 25.4% of the nation’s total child population, experiencing separation from at least one parent in 2015 [2]. While remittances from migrant parents have generally enhanced the household economic conditions, prolonged parent-child separation disrupts family structures and negatively impacts child development [3].
Early-life adversity (ELA), encompassing experiences such as maltreatment, trauma, and socioeconomic deprivation, disrupts the expected developmental environment and necessitates significant adaptation. Parent-child separation, recognized as one of the most severe forms of ELA due to early caregiving deprivation [4], substantially increases the risks of impaired neurodevelopment [5], mental health problems [6], and nutritional issues [7]. Some studies also report that it increases a child’s systemic inflammatory burden [8], and increase the risk of developing conditions such as diabetes and coronary heart disease later in life [9]. Both the weathering hypothesis and Belsky’s evolutionary-developmental framework suggest that adverse social exposures may accelerate biological processes, leading to earlier attainment of developmental milestones [10, 11]. A key mechanism underlying this association is accelerated biological aging [12], which has been assess using biomarkers such as DNA methylation patterns, puberty timing, and age at menarche [13, 14].
The oral cavity, serving as a critical interface between the body and external environment, provides unique insights into systemic aging. However, few studies have explored oral biological aging as an early indicator of ELA [15]. The eruption timing of first permanent molars (M1), a pivotal developmental milestone in children, is closely tied to overall growth [16]. Emerging evidence suggests that ELA may accelerate M1 eruption, positioning it as a potential oral biomarker of accelerated maturation [17]. While accelerated M1 eruption may represent a novel downstream effect of ELA-induced aging, buccal mucosal epithelial cell telomere length is already wide-established as a biomarker of biological aging. At the cellular level, telomeres—protective nucleoprotein complexes at chromosomal ends— shorten with each replication cycle, making them a robust indicator of biological aging [18]. Given their accessibility via non-invasive oral swabs, buccal epithelia cell telomeres are widely utilized in epidemiological research [19].
Our previous research demonstrated that prolonged parent-child separation accelerates telomere attrition in children’s oral epithelial cells [1], providing initial evidence that such separation hastens biological aging. Moreover, accumulating reports indicate that the detrimental effects of ELA may persist across generations, potentially influencing offspring health [20]. Studies of populations exposed to war, genocide and other major traumas strongly support the notion that parental ELA can shape offspring well-being [21]. Additionally, scholars propose that when both parents and children experience childhood adversity, the cumulative detrimental effects on offspring development may be amplified [22].
Despite compelling evidence linking early parent-child separation to adverse health outcomes, research on its intergenerational consequences remains limited. Expanding on existing findings, our study investigates the intergenerational transmission of parent-child separation, using the oral cavity as a window into biological aging. By integrating two biomarkers—oral epithelial cell telomere length (TL) and first permanent molar (M1) eruption timing—we aim to more comprehensively assess early risks of accelerated biological aging and explore the association between intergenerational separation experiences with these oral biomarkers. In recent years, numerous epidemiological studies have revealed associations between early-life adversity and oral diseases across the lifespan, such as higher rates of dental caries in childhood [23], poorer oral health in middle adulthood [24], and increased risk of edentulism in later life [25]. However, direct evidence specifically examining the impact of parent-child separation on oral health remains scarce. The oral manifestations of biological aging investigated in this study—significantly associated with various oral diseases including dental caries [26], periodontitis [27], oral submucous fibrosis [28], and head and neck cancer [29]—may help address this research gap. Furthermore, accelerated biological aging in childhood fundamentally reflects the accumulation of cellular and molecular damage, which can affect multiple physiological systems and negatively influence health throughout the life course [30]. Thus, our study underscores the importance of breaking the intergenerational cycle of parent-child separation to improve children’s oral health and overall health. Given reported sex differences in cohort studies and animal experiments [31], further investigations are needed to determine whether the intergenerational continuity of parent-child separation cumulatively enhances offspring susceptibility to accelerated biological aging in a sex-specific manner.
Methods
Study design and participants
The Nanling Early Childhood Growth Cohort investigates the potential effects of parent-child separation experiences on offspring biological aging in rural China. The study is based in Nanling County, a major labor-exporting region in southern Anhui Province. Data were collected from March to September 2024 through voluntary participation. To prospectively capture the initial stage of M1 throughout the entire high-risk window prior to its emergence, identify factors associated with early eruption, and ensure a statistically sufficient sample size of children, we set the study population age range at 3–6 years.
We recruited 2,347 preschool children aged 3–6 from 10 kindergartens in Nanling County. Parents completed an electronic questionnaire, while primary caregivers filled out a paper-based caregiver questionnaire in March 2024. After excluding invalid questionnaires (due to significant missing data) and children who had transferred schools or were absent, 2,019 children were included in the baseline physical examination, with 1,506 undergoing oral examinations. To determine the eruption status of children with M1 in the transitional eruption phase, we conducted a follow-up examination after six months. At the 6-month follow-up, 1,366 participants were re-examined for both oral health. Children with undetermined M1 eruption status at baseline or follow-up were excluded, leaving 895 children for the analysis of intergenerational parent-child separation and accelerated M1 eruption. The overall retention rate from initial recruitment to final analysis was 38.1% (895/2347). Due to the absence of established effect sizes in prior literature, no a priori power analysis was conducted. However, a post-hoc analysis using “G*Power” indicated that with the observed effect size at α = 0.05, our final sample (n = 895) achieved 82% power—demonstrating sufficient detection capability despite the initial limitation.
The telomere length (TL) subgroup (n = 230) was derived from the final sample of 895 children. Using 1:1 propensity score matching based on exposure status and all covariates, we constructed a balanced sub-cohort to examine the association between parent-child separation and TL while controlling for potential confounders. which successfully yielded matched children from the “exposed” and “non-exposed” groups. Therefore, the final subgroup for TL measurement and analysis consisted of 230 children. The study flowchart is presented in Fig. 1.
Fig. 1.
Study design and analytical workflow
Intergenerational continuity of parent-child separation
Intergenerational continuity in this study refers to situations where a father or mother who experienced separation from both parents during childhood later perpetuates early separation from their own child. Data on parent-child separation in both generations were self-reported by parents. The definition of left-behind children in policy documents issued by Chinese Ministry of Civil Affairs and other relevant national authorities is “a child aged 0–17 years who remains at the place of origin and cannot live with both parents, due to parents having migrated to work outside their home township or town for a period of six months or longer.” This definition has been widely adopted in research on left-behind children in China. Meanwhile, drawing on our research group’s previous studies on parent-child separation, we defined parent-child separation as a cumulative separation of more than six months within one year between both parents and their children [1, 32]. In the electronic parental questionnaire, mothers and fathers were asked to respond “yes” or “no” to the following questions: “Have you ever been separated from your children for more than 6 months in a single year?” “During your early life, were you ever separated from your parents for more than 6 months in a single year?” If either parent answered “yes” to the second question, it was coded as parental parent-child separation (i.e., separation experienced by the parent in their own childhood).
By cross-classifying separation experiences across two generations, children were categorized into four groups: no separation (neither children nor their parents experienced separation), only-child separation (children who experienced separation but whose parents did not), only-parent separation (children whose parents experienced separation but who themselves did not) and both separation (children and their parents who both experienced separation) .
Oral examination
Oral examinations were conducted in Kindergarten, with all children sitting in chairs, with natural sunlight used as the primary light source. Three licensed dentists performed all examinations after completing standardized training. Calibration with a gold-standard pediatric dentist reference demonstrated excellent inter-examiner agreement for assessing M1 eruption status and dental caries (Kappa = 0.85–0.92). The diagnostic criteria for assessing tooth eruption in this study was that any part of the crown had perforated the oral mucosa and was visible through it. Finally, the M1 eruption status is divided into: level 0: no, the tooth is not visible within the oral cavity; level 1: yes, the permanent tooth is clinically visible within the oral cavity. The dental caries status of the teeth was scored as the sum of the decayed, missing, and filled teeth in accordance with the 4th edition of Oral Health Surveys: Basic Methods published by the World Health Organization [33].
In this study, based on an epidemiologic survey by Ekstrand et al. [34]. In terms of the timing of tooth eruption, M1 eruption time < 6.1 years in girls was defined as earlier eruption, and M1 eruption time < 6.3 years in boys was defined as earlier eruption.
Genetic data processing
Before sampling, gargling was performed, and the buccal mucosa on both sides of the oral cavity was scraped 20 times with a cotton swab. The swabs were immediately frozen and stored at -80 °C until extraction. DNA for telomere analysis was collected using buccal swab samples, and isolated from buccal mucosal cell samples with the Qubit® dsDNA HS Kit (Thermo Fisher Scientific, USA).
Measures of telomere length
Relative telomere lengthwas measured via quantitative PCR, adapted from Cawthon’s method [35]. It was expressed as the T/S ratio: telomere abundance relative to that of the single-copy 36B4 gene. Primers for 36B4 were:
36B4F: 5’-CAGCAAGTGGGAAGGTGTAATCC-3’
36B4R: 5’-CCCATTCPATCATCAACGGGTACAA-3’
DNA was quantified using Takara’s SYBR® Premix DimerEraser™. PCR conditions: 95 °C for 1 min, then 40 cycles of 95 °C for 5s and 55 °C for 40s.
Cp values were averaged from 3 replicates, with ≥ 90% of samples requiring CV ≤ 5% for at least 2 replicates. Data screening: CV ≤ 5% = valid average; CV > 5% = exclude outlier and average remaining 2; if still CV > 5%, re-collect data.
T/S ratio = 2^(-ΔCp) (ΔCp = Mean CpTel2 - Mean Cp36B4), proportional to TL.
Early childhood adversity
The primary caregivers reported children’s early-life adversities (ELAs) through questionnaires,
The ten-item Adverse Childhood Experiences (ACE) questionnaire is a widely cited measure for ELA, which encompasses physical, verbal, and sexual abuse; physical and emotional neglect; witnessing violence between family members; having a family member with a mental illness or substance use disorder; incarceration of a family member; and parental divorce. Based on the original Kaiser-CDC ACE Study [36] and the synthesis literatures on ACEs [37], as well as our own research in the context of Chinese culture, the following 5 categories have been included: emotional neglect, emotional abuse, physical neglect, physical abuse, and peer bullying. Each adversity was coded as a binary variable (yes = 1, no = 0). The cumulative ELA score was calculated by summing all adversity dimensions, ranging from 0 to 5 points.
Physical examination
In accordance with WHO standard protocol [38], qualified testers used a mechanical height meter and a lever scale to measure the height and weight of children. Height was measured to the nearest 0.1 cm using a portable stadiometer, with children standing without shoes and positioned in the Frankfort horizontal plane. Weight was measured to the nearest 0.1 kg using a calibrated electronic digital scale, with children in lightweight clothing and without shoes. All measurements were performed in duplicate by trained inspectors, and the average of the two closest readings was used for analysis. After converting body weight and height to metric values, the body mass index (BMI) was calculated as kilograms per meter squared (kg/m2 ) to enable comparison.
Covariate
The study included the following covariates: age, sex, BMI, birthweights, and Child feeding practices (exclusive only breast milk, breast milk and formula milk, only formula milk, or other); parental age and education level (categorized as middle school and below, high school or technical school, college degree, bachelor’s degree or above), Family income (categorized as low, mod and high ), Child’s ELAs score, caries. The aforementioned covariate information was obtained through questionnaires completed by the primary caregivers, while the dental caries data were recorded during the oral examinations.
Statistical analysis
First, We used Multiple Imputation by Chained Equations via R’s “mice” package (4.4.3) to handle missing data. We generated 20 imputed datasets with 10 iterations for stability, incorporating all analysis variables via Predictive Mean Matching. Results were pooled using Rubin’s rules. In our study, we had two primary outcome variables: (1) Accelerated first molar eruption, which was operationalized as a binary variable; and (2) Telomere length, which was treated as a continuous variable. We described the basic characteristics of the participants with mean (SD) for continuous variables and count (percentage) for categorical variables, respectively. Group differences in baseline characteristics and biological aging markers (M1 accelerated eruption, TL) across parent-child separation groups were assessed using χ2 tests and ANOVA, with gender-stratified comparisons performed for biological aging indicators. Logistic regression and linear regression models were employed to examine the association between intergenerational parent-child separation history and offspring’s M1 accelerated eruption and TL, with evaluation of gender-specific effects. All models were adjusted for covariates including: age, sex, parental age, BMI, birth weight, feeding practices, childhood ELAs, household income, parental education level, chewing habits, and caries. All statistical analyses were performed using SPSS 25.0, with the significance level set at α = 0.05.
Results
Sample characteristics
Table 1 presented demographic and lifestyle information grouped by different parent-child separation experiences. The study cohort comprised 895 preschool children (mean age = 6.01 ± 0.41 years; 45.4% boys [n = 406], 54.6% girls [n = 489]). 114 (28.1%) boys and 135 (27.6%) girls were categorized in the“only-parent separation group”; 67 (16.5%) boys and 89 (18.2%) girls were in the“only-child separation group”; 76 (18.7%) boys and 103 (21.1%) girls were in the“both separation group”; the remaining 149 (36.7%) boys and 162 (33.1%) girls belonged to the“no separation group”.
Table 1.
Comparison of basic information of children in different parent-child separation groups
| Variables | N | Intergenerational parent-child separation | χ2 | |||
|---|---|---|---|---|---|---|
| No separation | Only-parent separation |
Only-child separation | Both separation | |||
| Sex (n, %) | 1.81 | |||||
| Boys | 406 (45.4) | 149 (47.9) | 114 (45.8) | 67 (42.9) | 76 (42.5) | |
| Girls | 489 (54.6) | 162 (52.1) | 135 (54.2) | 89 (57.1) | 103 (57.5) | |
| Age of children (year) | 6.0 ± 0.4 | 6.0 ± 0.4 | 6.0 ± 0.4 | 6.0 ± 0.4 | 6.0 ± 0.4 | 2.18 |
| Age of mothers (year) | 34.9 ± 5.2 | 36.3 ± 5.0 | 34.0 ± 5.0 | 35.7 ± 5.1 | 33.3 ± 4.9 | 17.7*** |
| Age of fathers (year) | 36.1 ± 5.2 | 37.1 ± 5.2 | 35.5 ± 5.2 | 36.7 ± 5.3 | 34.9 ± 4.7 | 8.99*** |
| Baseline child BMI (kg/m2) | 16.0 ± 2.4 | 15.9 ± 2.5 | 15.8 ± 2.7 | 15.8 ± 2.3 | 16.1 ± 2.4 | 0.41 |
| Birthweight (g) | 3276.9 ± 489.8 | 3328.7 ± 496.1 | 3338.8 ± 471.2 | 3259.6 ± 512.5 | 3199.4 ± 476.0 | 2.91* |
| Child feeding practices | 9.48 | |||||
| Only breast milk | 486 (54.3) | 177 (56.9) | 144 (57.9) | 71 (45.5) | 94 (52.5) | |
|
Breast milk and formula milk |
284 (31.7) | 90 (28.9) | 77 (30.9) | 59 (37.9) | 58 (32.4) | |
| Only formula milk | 117 (13.1) | 40 (12.9) | 27 (10.9) | 25 (16.0) | 25 (14.0) | |
| Other | 8 (0.9) | 4 (1.3) | 1 (0.3) | 1 (0.6) | 2 (1.1) | |
| Child’s ELAs score (points) | 2.9 ± 2.0 | 2.7 ± 2.1 | 3.0 ± 2.0 | 2.7 ± 2.0 | 3.3 ± 2.0 | 4.23** |
| Household income | 23.75*** | |||||
| Low (< 5000/month) | 311 (34.8) | 139 (44.7) | 65 (26.1) | 52 (33.3) | 55 (30.7) | |
| Moderate | 344 (38.4) | 103 (33.1) | 110 (44.2) | 58 (37.2) | 73 (40.8) | |
| High (> 10,000/month) | 240 (26.8) | 69 (22.2) | 74 (29.7) | 46 (29.5) | 51 (28.5) | |
| Parental highest educational level | ||||||
| Middle school and below | 321 (35.9) | 135 (43.4) | 68 (27.3) | 60 (8.5) | 58 (32.4) | 20.19* |
| High school or technical school | 242 (27.0) | 76 (24.4) | 73 (29.3) | 44 (28.2) | 49 (27.4) | |
| College degree | 196 (21.9) | 56 (18.0) | 65 (26.1) | 28 (17.9) | 47 (26.3) | |
| Bachelor’s degree or above | 136 (25.2) | 44 (14.2) | 43 (17.3) | 24 (15.4) | 25 (14.1) | |
| Caries | 3.4 ± 3.9 | 3.5 ± 4.0 | 3.3 ± 3.8 | 3.5 ± 4.2 | 3.4 ± 3.9 | 0.19 |
ELAs refers to Early-life adversities
* p ≤ 0.05 ** p ≤ 0.01 *** p ≤ 0.001
The analysis revealed significant between-group differences in key demographic and socioeconomic factors, including maternal age, paternal age, birth weight, children’s early life adversities (ELAs), family income, and highest parental education level. After conducting two oral examinations at baseline and follow-up to exclude children with indeterminate M1 eruption status, our final study comprised 895 children. The overall prevalence of premature M1 eruption was 28.7% (257/895), with a higher rate observed in boys (31.8%, 129/406) compared to girls (26.2%, 128/489).
In the subset of 230 children with available telomere length measurements, the mean telomere length of oral epithelial cells was 0.87 ± 0.23. Notably, boys exhibited marginally longer telomeres (0.88 ± 0.24) compared to girls (0.86 ± 0.24).
Association between intergenerational parent-child separation and M1 eruption status in preschool children
As illustrated in Table 2, the detection rate of M1 accelerated eruption showed significant differences across intergenerational parent-child separation groups (χ²=9.69, p = 0.02). Specifically, children in the both separation group exhibited significantly higher M1 accelerated eruption rates than those in the no separation group (37.4% vs. 28.6%). However, this difference was only observed in boys (χ²=9.32, p = 0.03) and not in girls.
Table 2.
Comparison of M1 accelerated eruption in preschool children from different intergenerational parent-child separation groups
| Early eruption of M1 | N | Intergenerational parent-child separation | χ2 | P-values | |||
|---|---|---|---|---|---|---|---|
| No separation | Only-parent separation |
Only-child separation | Both separation | ||||
| Total | 9.69 | 0.02 | |||||
| Yes | 257 (28.7) | 89 (28.6) | 60 (24.1) | 41 (26.3) | 67 (37.4) | ||
| No | 638 (71.3) | 222 (71.4) | 189 (75.9) | 115 (73.7) | 112 (72.6) | ||
| Boys | 9.32 | 0.03 | |||||
| Yes | 129 (31.8) | 50 (33.6) | 26 (22.8) | 20 (29.9) | 33 (43.4) | ||
| No | 277 (68.2) | 99 (66.4) | 88 (77.2) | 47 (70.1) | 43 (56.6) | ||
| Girls | 3.24 | 0.36 | |||||
| Yes | 128 (26.2) | 39 (24.1) | 34 (25.2) | 21 (23.6) | 34 (33.0) | ||
| No | 361 (73.8) | 123 (75.9) | 101 (74.8) | 68 (76.4) | 69 (67.0) | ||
As shown in Table 3, after full adjustment for covariates, intergenerational continuity of parent-child separation was significantly associated with offspring M1 eruption status. Children in the ‘both separation’ group had a 2.03-fold higher risk of accelerated M1 eruption (95% CI: 1.24–3.33, p = 0.005) compared to the no-separation group. Sex-stratified analyses confirmed this association in both boys and girls.
Table 3.
Logistic regression analysis of intergenerational parent-child separation and M1 earlier eruption in offspring
| Variables | Earlier M1 eruption | |||
|---|---|---|---|---|
| Unadjusted model | Adjusted model | |||
| OR (95%) CI | P-values | OR (95%) CI | P-values | |
| Parent-child separation | ||||
| No separation | Reference | Reference | ||
| Only-parent separation | 0.79 (0.54, 1.16) | 0.23 | 1.11 (0.69, 1.77) | 0.67 |
| Only-child separation | 0.89 (0.58, 1.37) | 0.6 | 1.29 (0.16, 2.78) | 0.35 |
| Both separation | 1.49 (1.01, 2.20) | 0.04 | 2.03 (1.24, 3.33) | 0.005 |
| Boys | ||||
| No separation | Reference | Reference | ||
| Only-parent separation | 0.59 (0.34, 1.02) | 0.06 | 0.66 (0.34, 1.25) | 0.21 |
| Only-child separation | 0.84 (0.45, 1.57) | 0.59 | 0.99 (0.49, 2.05) | 0.99 |
| Both separation | 1.52 (0.86, 2.68) | 0.15 | 1.99 (1.01, 3.94) | 0.04 |
| Girls | ||||
| No separation | Reference | Reference | ||
| Only-parent separation | 1.06 (0.63, 1.80) | 0.83 | 2.08(1.01, 4.30) | 0.04 |
| Only-child separation | 0.97 (0.53, 1.79) | 0.93 | 2.08(0.98, 4.74) | 0.08 |
| Both separation | 1.55 (0.90, 2.68) | 0.11 | 2.45(1.35, 5.32) | 0.02 |
Association between intergenerational Parent-Child separation and TL in preschool children
Figure 2 presented the TL comparisons among the 230 children. Intergenerational continuity of parent-child separation showed significant effects on TL. Compared to children with no parent-child separation, TL were significantly shorter among preschoolers in only-parent separation, only-child separation, both separation (0.78 ± 0.25 vs. 0.83 ± 0.21 vs. 0.84 ± 0.23 vs. 0.87 ± 0.23; F = 13.88, p < 0.001). Sex-stratified analyses showed that all three separation groups exhibited significantly shorter TL than the no-separation group in boys. In contrast, among girls, only those with parental childhood separation histories showed no significant TL difference compared to the no-separation group.
Fig. 2.
Comparison of TL in preschool children from different intergenerational parent-child separation groups
Table 4 presented after adjusting for all covariates, intergenerational parent-child separation significantly negatively associated with offspring TL. Specifically, children’s TL in only-parent separation (β: -0.17, 95% CI: -0.26 to -0.08, p < 0.001), only-child separation (β: -0.18, 95% CI: -0.27 to -0.09, p < 0.001), and both separation (β: -0.23, 95% CI: -0.32 to -0.14, p < 0.001) groups were 17%, 18%, and 23% shorter than controls, respectively. After further consideration of sex, the effects of all three types of intergenerational parent-child separation histories on child TL were equally present in boys, only the intergenerational continuity of parent-child separation had a significant effect on offspring TL in girls (β:-0.19, 95% CI:-0.35 to -0.03, p = 0.02).
Table 4.
Multivariate linear regressions for intergenerational parent-child separation and telomere length in offspring oral cells
| Variables | Oral epithelial cell telomere length | |||
|---|---|---|---|---|
| Unadjusted model | Adjusted model | |||
| β (95%) CI | P-values | β (95%) CI | P-values | |
| Parent-child separation | ||||
| No separation | Reference | Reference | ||
| Only-parent separation | -0.19 (-0.24, -0.10) | < 0.001 | -0.17 (-0.26, -0.08) | < 0.001 |
| Only-child separation | -0.20 (-0.30, -0.11) | < 0.001 | -0.18(-0.27, -0.09) | < 0.001 |
| Both separation | -0.23 (-0.32, -0.15) | < 0.001 | -0.23(-0.32, -0.14) | < 0.001 |
| Boys | ||||
| No separation | Reference | Reference | ||
| Only-parent separation | -0.23 (-0.34, -0.12) | < 0.001 | -0.24 (-0.37, -0.11) | < 0.001 |
| Only-child separation | -0.18 (-0.28, -0.07) | 0.001 | -0.21 (-0.32, -0.09) | < 0.001 |
| Both separation | -0.28 (-0.39, -0.17) | < 0.001 | -0.31 (-0.44, -0.19) | < 0.001 |
| Girls | ||||
| No separation | Reference | Reference | ||
| Only-parent separation | -0.17 (-0.30, -0.04) | 0.014 | -0.13 (-0.28, 0.02) | 0.1 |
| Only-child separation | -0.22 (-0.3, -0.09) | 0.002 | -0.14 (-0.3, 0.02) | 0.09 |
| Both separation | -0.23 (-0.36, -0.09) | 0.001 | -0.19 (-0.35, 0.03) | 0.02 |
Sensitivity analysis
Table S1 and S2 showed the results of the sensitivity analysis. Paternal intergenerational pathway analysis showed that the risk of M1 accelerated eruption was 1.69, 1.81, and 1.90 times higher in the only-father separation, only-child separation and the both-separation groups respectively, compared with that in the control group. Correspondingly, these groups displayed progressive telomere shortening, with TL reductions of 20%, 19%, and 24% respectively relative to controls.
In contrast, maternal pathway analysis revealed more selective effects. A significant 1.81-fold increased risk of M1 accelerated eruption was observed exclusively in children experiencing both maternal and current separation. Regarding telomere length, only maternal childhood separation history significantly influenced offspring TL, without additional effects from concurrent child separation.
Discussion
In the present study of parent-offspring dyads who lived in a major labor-exporting county resembling a population living in an intergenerational cycle of parent-child separation, we investigated associations between intergenerational separation patterns with intraoral biomarkers of biological aging among preschool children. Our key finding revealed that children experiencing intergenerational continuity of separation (where both parents and child had separation histories) faced a 2.03-fold increased risk of accelerated first molar (M1) eruption compared to non-exposed children. Notably, this association was specific to the intergenerational exposure group, as neither children with only parental separation histories nor those experiencing only current separation showed elevated risk of accelerated M1 eruption.
When telomere length (TL) —another key biomarker of biological aging—was analyzed, children in the only-parent separation, only-child separation, and both separation groups exhibited 17%, 18%, and 23% shorter TL, respectively, compared to the no-separation group. These findings suggested that the cumulative effects of intergenerational parent-child separation significantly influence both biomarkers of biological aging in offspring. Sensitivity analyses further indicated that intergenerational separation accelerates biological aging risk in offspring through both paternal and maternal transmission pathways, though the paternal pathway appears to exert a stronger effect.
Our findings aligned with established evidence demonstrating ELA-induced stress accelerates M1 eruption [17] and corroborate previous reports linking parent-child separation with telomere attrition [18, 39]. While existing research has primarily examined single-generation exposures, this study represents, to our knowledge, the first investigation of intergenerational transmission effects - specifically how compound adversity from parental and offspring experiences of early-life separation influences offspring biological aging as measured through oral biomarkers. These intraoral biomarkers offer dual clinical value: they serve as sensitive indicators of systemic biological aging processes tied to accelerated development and future health risks, while also directly predicting oral health outcomes. Substantial evidence have indicated that accelerated tooth eruption predisposes to developmental defects [26], increasing caries susceptibility and compromising root formation, ultimately yielding less stable dentition. Similarly, shortened telomeres show consistent associations with oral pathologies including periodontitis [27], oral submucous fibrosis [28], and head/neck malignancies [29]. These findings underscored the critical need to disrupt intergenerational cycles of parent-child separation, with important implications for both oral and systemic health interventions. Our work provided novel mechanistic insights into how early adversity becomes biologically embedded across generations, offering valuable theoretical and practical guidance for public health initiatives.
Several possible mechanisms might explain the observed associations. The ‘transgenerational epigenetic inheritance’ hypothesis [21] posits that adverse preconception environmental factors induce gametic epigenetic modifications, which may manifest in offspring behavioral phenotypes and developmental trajectories, animal models have provided mechanistic evidence for pre-conceptual parental environmental influences through germline-mediated non-genetic inheritance [40]. Notably, shortened parental TL may be directly transmitted to offspring via epigenetic mechanisms, with lifelong adversity [41] identified as a key determinant of parental TL attrition. Paternal environmental-induced intergenerational epigenetic inheritance may occur through the sperm cell-specific epigenomic (RNA, chromatin, DNA methylation) profile, in which microRNAs may serve as key participants in the intergenerational and transgenerational transmission of acquired traits. Furthermore, we speculate that socio-psychological factors may contribute to the differences in paternal and maternal intergenerational transmission. Paternal childhood trauma may establish a persistent adverse microenvironment by influencing psychological well-being and parenting behaviors, whereas mothers, potentially acting as central buffering figures, may mitigate the impact of their own adverse experiences, resulting in more statistically prominent paternal risk associations in the analysis. This may partially explain the sensitivity differences between paternal and maternal inheritance [42]. Furthermore, parental ELAs may program offspring stress response systems via intrauterine mechanisms [43], increasing vulnerability to subsequent stressors. This intersects with child-autonomous HPA-axis activation from direct ELA exposure, creating a dual-risk paradigm that elevates the key stress biomarkers cortisol [44] and inflammatory markers [45]. Given chronic inflammation’s established role as the primary driver of aging and age-related pathologies [46], human evidence demonstrated inflammation-induced telomere attrition [47], and this dual-stress synergy accelerates alveolar bone remodeling, serve as a plausible mechanistic basis for accelerated tooth eruption.
Our sex-stratified analyses revealed that intergenerational parent-child separation significantly influenced both M1 eruption timing and telomere length (TL) in boys and girls, though with notable gender differences in biomarker sensitivity. Regarding M1 eruption, both genders showed patterns consistent with the overall sample, though girls exhibited a potentially stronger association. In TL analyses, gender-specific patterns emerged more distinctly: among girls, only those experiencing both-generation separation showed significantly shorter TL (19% reduction) compared to controls, whereas boys demonstrated TL attrition across all separation subgroups. These findings contributed to a limited and sometimes contradictory literature on gender differences in biological aging biomarkers [48–50]. The underlying mechanisms driving these sex-specific intergenerational effects remain incompletely understood and warrant further investigation through targeted studies with larger sample sizes.
Several limitations merit consideration. First, while validated questionnaires were used, recall bias in reporting parent-child separation may persist, potentially underestimating its true association with biological aging. Second, although oral exams followed standardized protocols, the extended follow-up intervals may have introduced measurement error in determining exact eruption timing, likely diluting observed effect sizes. Third, substantial sample attrition occurred; while attrition analysis showed limited demographic differences, selection bias from unmeasured factors cannot be ruled out and may affect generalizability. Fourth, despite adjusting for known confounders, residual confounding (e.g., by neighborhood or social factors) may remain. Fifth, early molar eruption as an aging marker remains exploratory, and unmeasured genetic confounding is possible. Similarly, sex-specific analyses were underpowered and require further validation. Finally, the underrepresentation of the most vulnerable children may limit generalizability and lead to effect underestimation. Future studies should adopt a multifaceted approach to address current limitations, such as refining questionnaires and sampling strategies to reduce bias, incorporating broader covariates and genetic data to minimize confounding, and establishing cohort follow-ups to investigate causality and underlying biological mechanisms.
In summary, Our findings highlight that early first molar eruption and telomere shortening may serve as accessible biomarkers of accelerated biological aging in children exposed to intergenerational parent-child separation. From a clinical perspective, this suggests that dental professionals—particularly in primary care or school-based screening settings—could use early molar eruption as a low-cost, non-invasive indicator to identify children who may be at risk for broader health challenges. When such signs are observed, a referral pathway involving pediatricians and mental health professionals could be initiated, enabling early assessment and holistic support for the child’s physical and emotional well-being.
Conclusion
Our study provided the first evidence demonstrating the detrimental effects of intergenerational parent-child separation on observable and testable biological aging indicators in children’s oral cavity. Our findings highlight the clinical significance of two key indicators: (1) accelerated eruption of first permanent molars (M1) as an observable developmental milestone, and (2) telomere length (TL) in oral epithelial cells as a marker of cellular aging. These biomarkers offer valuable insights for assessing children’s developmental risks and predisposition to future oral health complications. Moving forward, research should focus on three critical directions: (1) replicating these findings in larger, diverse populations; (2) investigating how the timing and nature of intergenerational separation influence different dimensions of biological aging; and (3) elucidating the mechanistic pathways through which these effects ultimately contribute to health disparities across the lifespan.
Supplementary Information
Acknowledgements
The authors would like to thank and acknowledge all investigators and staff, as well as the study participants.
Abbreviations
- M1
the first perment molar
- TL
telomere length
- ELA
Early-life adversity
- SD
Standard deviation
- CI
Confidence interval
- OR
Odds ratio
Authors’ contributions
X.Y. contributed to conception and design, acquisition, analysis, and interpretation, drafted the manuscript, and critically revised it; Y.Z. and X.L. contributed to acquisition, analysis, and interpretation, drafted the manuscript; K.M. contributed to acquisition, analysis, and interpretation; Y.S. and X.C. contributed to contributed to conception and design, critically revised manuscript, gave final approval, and agreed to be accountable for all aspects of work, ensuring integrity and accuracy. All authors gave their final approval and agreed to be accountable for all aspects of the work.
Funding
National Natural Science Foundation of China (82173537).
Data availability
The datasets generated and analyzed during the current study are not publicly available due to privacy and ethical restrictions. For those interested in this study, please make reasonable requests to obtain it from the corresponding author.
Declarations
Ethics approval and consent to participate
The Anhui Medical University provided ethical approval of the survey (Project number 20180082). Before the survey, informed consent was obtained from all participants and their parents or primary caregivers. All the obtained information from participants was handled voluntarily, confidentially, and anonymously. Our study adhered to the Declaration of Helsinki.
Consent for publication
Not applicable.
Competing interests
The authors declare no competing interests.
Footnotes
Publisher’s note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Contributor Information
Ying Sun, Email: yingsun@ahmu.edu.cn.
Xin Chen, Email: chenxinkq2672@126.com, Email: chenxin2672@ahmu.edu.cn.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Data Availability Statement
The datasets generated and analyzed during the current study are not publicly available due to privacy and ethical restrictions. For those interested in this study, please make reasonable requests to obtain it from the corresponding author.