A study published in the Journal of Public Health found that the mental health of low-income service workers in London improved if they had higher wages to cover the generally higher living expenses of the city.

“Working poverty has become a major public health concern in recent times, and low-paid, insecure employment has been widely linked to poor psychological wellbeing,” the study notes in its Background. “The objective of this study is to investigate whether working for a [London Living Wage] employer predicted higher levels of psychological wellbeing among low-wage service sector employees.”

The London Living Wage, or LLW, is a social campaign started in 2001 that has pushed for higher pay based on higher living expenses. In London, one of the more expensive cities in the world, around 200 employers agreed to take part in the movement and offer higher living wages to their employees.

The LLW in 2011 was set to 8.30 British pounds per hour, the equivalent of U.S. $13, compared to the UK minimum wage of 6.08 pounds per hour, just over U.S. $9. In 2012, London Mayor Boris Johnson raised the living wage to 8.55 pounds per hour.

The “wellbeing” scale – the Warwick-Edinburgh Mental Wellbeing Scale – that was used to measure 173 people working for LLW employers and 127 for non-LLW employers is not a clinical tool, and cannot be used to decipher whether a person is healthy or not. It can, however, measure “optimism about the future, feeling useful, feeling relaxed, feeling interested in other people, having energy to spare, thinking clearly, feeling good about yourself, feeling close to other people, feeling confident, making your own mind up about things, feeling loved, being interested in new things and feeling cheerful,” Ellen Flint, a researcher of social and environmental health at the London School of Hygiene and Tropical Medicine and lead author of the study, said.

The researchers found that people who worked for an employer abiding by the LLW standard had “significantly higher psychological wellbeing on average” compared to those who didn’t. Half of the LLW employees scored above average for mental health, while 34 percent of non-LLW employees scored higher than average.

The authors of the study noted that there are plenty of factors affecting mental health for people working many hours at low-income jobs, including stress caused by debt, providing for their children, and social isolation.

The BBC reports that in 2012, Major Johnson said: "By building motivated, dedicated work forces the living wage helps businesses to boost the bottom line and ensures that hard working people who contribute to London's success can enjoy a decent standard of living."