(Bloomberg) — To limit the rising cost of health care, companies are increasingly turning to private insurance exchanges that let employees shop for plans, according to research from Accenture.

About 6 million people got health insurance coverage via such online portals this year, up from 3 million in 2014, the consulting firm said Tuesday. Accenture expects that to jump to 40 million people, or about a quarter of those who get insurance at work, in 2018.

The shift could place more of the financial burden of health care on workers, though it can save employers money and may bolster earnings at benefits consultants like Towers Watson & Co. and Aon. Towers Watson gets about 10 percent of its sales by operating the online portals for its clients, and exchange revenue grew the fastest among the company's major business lines in the final three months of last year.