Linking childhood allostatic load, early adversity and the emergence of mental health symptoms in early adulthood: Analysis of the ALSPAC longitudinal birth cohort.

Background: It has been well-established that the allostatic load (AL) index, a cumulative score of multi-system dysregulation in response to chronic stress, is significantly increased at the time of a psychiatric diagnosis. However, no studies have investigated if there is an association between the AL index in childhood and the later development of mental health symptoms in young adults.

Methods: Using data from the Avon Longitudinal Study of Parents and Children (ALSPAC), a population cohort from Bristol, United Kingdom, we investigated the AL index at age 9 years and the risks for mental health symptoms at age 24 years. We used multinomial logistic regression analysis to investigate the association between AL threshold (categorised into bottom third: AL index ≤ 7, middle third: AL index = 7.1-9.9, and top third: AL index ≥ 10) and mental health symptoms while adjusting for sex, the age of mother at delivery, and social class. We used a relative risk ratio (RRR) and 95 % confidence interval(CI) for each variable. We further investigated the association between adverse childhood experiences (ACEs) and mental health symptoms.

Results: We identified a significant association between sex and mental health symptoms, with more females (59 % vs 41 %) showing mental health symptoms than males. We found no direct association between the AL index at age 9 and the later development of mental health symptoms. However, an RRR analysis showed that individuals in the middle and the top third of the AL index had an RRR of 1.99 and 2.20, respectively, to develop mental health symptoms if they were females. We found that individuals who experienced ACE had a much higher risk of developing mental health symptoms as young adults, with the adjusted RRR of 5.39 (95 % CI: 3.00;9.67), 6.79 (95 % CI: 2.55; 18.1), and 2.10 (95 % CI: 0.37;11.8) for neglect, physical and sexual abuse, respectively, in individuals with mood disorder symptoms. The adjusted RRR for neglect and physical and sexual abuse in individuals with psychotic symptoms was 0.99 (95 % CI: 0.37; 2.59), 2.92 (95 % CI: 0.35; 24.4), and 10.5 (95 % CI: 0.99; 112), respectively.

Conclusion: Although the AL index in childhood was not directly associated with the later development of psychotic and mood disorder symptoms in this cohort, females in the higher tertiles of the AL index measured at 9 years of age had an elevated risk of mental health symptoms as young adults. In line with previous work, a strong association was identified between childhood adversity and mental health symptoms in young adulthood. These results highlight the importance of considering the impact of early stress on biological embedding and the later emergence of mental health problems, especially in females.