Companies have long embraced workplace wellness programs as a way to improve workers’ health and reduce overall medical spending, but a new study may prompt employers to rethink those efforts.

The study, published on Tuesday in JAMA, a medical journal, looked at the experience of 33,000 workers at BJ’s Wholesale Club, a retailer, over a year and a half.

While workers who enrolled in the wellness program reported that they learned to exercise more and watch their weight, the research found no significant differences in outcomes like lower blood pressure or sugar levels and other health measures. And it found no significant reduction in workers’ health care costs.

“These findings may temper expectations about the financial return on investment that wellness programs can deliver in the short term,” conclude the study’s authors, Dr. Zirui Song, a health policy researcher at Harvard Medical School, and Katherine Baicker, dean of the University of Chicago Harris School of Public Policy.