If you’re looking for your organization’s employee wellness plan to pay dividends in the form of lower healthcare costs and absenteeism rates as well as higher job tenure and performance, then a study by Harvard researchers published last week in JAMA, the journal of the American Medical Association, will give you pause.

The randomized clinical trial — the most rigorous kind of study — included about 32,974 employees of a large, multistate warehouse retail company. At 20 work sites, 4,037 employees had access to wellness programming on nutrition, physical activity, stress reduction and other related topics. At 140 other work sites, 28,937 employees had no wellness programming and were used for comparison.

Zirui Song, M.D., Ph.D., and Katherine Baicker, Ph.D., analyzed surveys completed by the employees and compared healthcare spending and use and employment outcomes.

They found that, after 18 months, work sites with wellness programming had higher rates of employees reporting that they exercised more regularly and were actively managing their weight. No significant differences, however, were found in 27 self-reported health and behavioral measures, such as employees’ overall health, sleep quality and food choices; 10 clinical measures of health, such as cholesterol, blood pressure and body mass index; 38 measures related to healthcare spending and use (doctor’s visits, medical tests, procedures, prescriptions, etc.); and three employment outcomes: absenteeism, job tenure and performance.

So should you ditch your wellness plan? No, the authors said. One reason is that their research may not be applicable to all types of workplaces and workers.

They noted, however, that the findings might temper employer expectations about their ability to lower healthcare costs and improve employee health and productivity in the short term.

Employers and wellness companies, Song and Baicker advised, should “critically assess the programs they are offering and increase their willingness to innovate, test, and evaluate novel designs.”

Employers may have more success meeting their corporate goals if they focus on those workers who are at greater risk for poor health or already are in poor health, according to the author of an accompanying editorial. And, Jean Marie Abraham, Ph.D., of the University of Minnesota added, they can support employees in meeting their wellness goals through actions such as establishing anti-smoking policies and making healthful foods and exercise facilities available at the workplace.

Wellness plans, she said, “should be considered a work in progress.”