Exposure to childhood trauma or adverse adulthood experiences (AAEs) may increase depression risk. However, the relationships between these factors and age of depression onset remain unclear.

We aimed to investigate the associations of childhood trauma and AAEs with depression risk across life stages, and their joint effects on lifetime depression risk.

A total of 118 164 participants without prior depression from UK Biobank (UKB) were included. Adverse experiences during childhood and adulthood were assessed through the online mental health questionnaire in 2016, primarily including physical neglect, physical abuse, emotional neglect, emotional abuse and sexual abuse. Cox proportional hazard regression models were used to explore the independent and joint effects of childhood trauma and AAEs on the age of depression onset.

In the multivariable-adjusted models, compared with low childhood trauma, high childhood trauma was associated with higher risk of depression occurring in early adulthood [hazard ratio 2.35, 95% CIs: 2.12–2.59] and middle adulthood (hazard ratio 1.86, 95% CIs: 1.67–2.07). Likewise, in comparison with lower levels of AAEs, higher levels were significantly associated with an elevated risk of depression during middle adulthood (hazard ratio 2.71, 95% CIs: 2.26–3.25). In joint analyses we found that, compared with individuals with low AAEs and low childhood trauma, those with low AAEs and high childhood trauma (hazard ratio 1.80, 95% CIs: 1.41–2.30) and those with high AAEs and low childhood trauma (hazard ratio 1.74, 95% CIs: 1.35–2.26) exhibited similarly significant effects on the risk of depression, suggesting that childhood trauma and AAEs had contributed equally to lifetime depression (P > 0.05).

Exposure to childhood trauma or AAEs presented a more detrimental effect on the early onset of depression compared with later stages throughout the lifespan. Our findings advise paying attention to traumatic events at any life stage, and the instigation of prompt intervention strategies following traumatic events, to minimise the risk of lifetime depression.