There’s convincing data that employee wellness programs can save companies money on health care and related costs. But new research paints an even more uplifting portrait: such initiatives could give workers a productivity boost equal to gaining an extra day of work per month.

Researchers from the University of California, Riverside, UCLA and Washington University in Saint Louis offered a voluntary wellness program to employees at a Midwest-based industrial laundry company. They collected data on the employees’ health and productivity for a total of three years and will publish their results in the journal Management Science, according to a press release on the findings.

Wellness programs can take a lot of forms, from classes on how to eat better to stress reduction initiatives. For this study, volunteers (about 85 percent of employees opted in) received a free health exam, an educational seminar led by a registered nurse and a personalized report on their current health, which included recommendations on where they could improve, according to the press release.

Researchers then compared participants’ medical information with data on their productivity and found that the wellness initiative gave workers a five percent productivity boost, on average—the equivalent of working an extra day per month.

The exact reasons for the productivity spikes weren’t clear, but lead study author Timothy Gubler, assistant professor of management in the School of Business at UCR, points to two main factors. One is that employees might be happier, more motivated and more grateful if they found out about a previously unknown health problem because of the program. (And that happened during this study, according to Gubler.) About two-thirds of the employees had a medical condition when screened, and “sick” employees who showed improvements in health “increased productivity levels that averaged 11 percent.”

The second reason is, essentially, that people who prioritize their health are generally more productive. So it makes sense that the biggest productivity boosts went to employees who improved their diet and exercise the most, and Gubler notes that wellness programs can positively affect “mood, energy, and ultimately increase their productivity through increased capability.”

These findings add more weight to the idea that employee wellness matters regardless of what your role is within a company or what industry you work in. Gubler summed it up well: “The result is healthier and happier employees who are not only less expensive and less absent, but also more productive.”

Read more about the findings here