Most U.S. workers who have health plans through their employers must cover at least some expenses before their insurance kicks in, and those out-of-pocket costs have risen eight times as fast as wages, a closely watched study found.

American employers are the largest source of health coverage in the country, insuring about 152 million people. Over the past decade, they've asked workers to shoulder a greater and greater share of medical costs, in a system-wide redistribution of risk that shows no signs of abating.

New data from an annual survey by the Kaiser Family Foundation, a health-policy research group, shows health benefits are steadily becoming more expensive for both workers and employers. As total costs increase, higher deductibles expose workers to increased financial risk when they fall ill.