Background Over the past decade, single mothers have experienced increasing work requirements both in the UK and in other developed countries. However, despite significant rises in maternal employment over the past decade, little is known how increasing working hours may have affected their mental health. The aim of our study was to investigate the impact of increasing working hours on mental health of single mothers, and to compare this relationship to that for partnered mothers.

Methods We used 13 waves of the UK Household Longitudinal Study (2009-2023) to estimate the relationship between changing working hour categories (1-16 hour per week vs. 17-25; 26-35; 36-40; and 41+) and mental health using fixed-effects models. We also investigated the role of potential mechanisms linking higher working hours and mental health, including role strain and additional income.

Results Our findings suggest that increasing working hours from low (1-16 hours per week) to higher categories has a negative and progressively worsening relationship with the mental health of single mothers. Increasing hours to 17-25, 26-35, 36-40, and 41+ is associated with lower GHQ-12 scores by -0.7 [-1.201,-0.194], -0.5 [-1.120,0.058], -0.8 [-1.504,-0.091] , and -1.1 [-1.876,-0.378] respectively. For partnered mothers, there is no significant relationship with mental health across any of the higher working hour categories. Further analyses suggest increased role strain for single mothers as a mechanism helping explain these differences.

Conclusion We have found that higher working hours relative to part-time may be contributing to the worsening mental health of single mothers, at least in part due to increased role strain of having to balance work and family responsibilities. Such effects should be considered when developing future welfare policies for single mothers, to ensure that greater work requirements do not undermine the mental health of the already vulnerable population group.