Study co-author Laura Robinson said the study showed that single working mothers had poorer physical and mental health than partnered mums.

However, she said, while the physical health of partnered mothers stayed the same regardless of how many hours they worked, this was not the case for single mothers.

"Surprisingly, sole parent working mothers had better physical health if they worked more than 40 hours per week, rather than working fewer hours," Ms Robinson said.

"We're not entirely sure why ... perhaps they are more established in their careers and have more flexibility. Perhaps they have a higher income and better access to resources like childcare."

The study, by the School of Psychology and Centre for Health Initiatives, also looked at the link between health and social support.

"Sole mothers often have poorer social support, which can have a big impact on their mental health," Ms Robinson said.

"Organisations can help by increasing social support in the workplace through things like peer support groups."