Bank of America Corp. is seeing record growth in its health savings account business as health care costs continue to rise and employers shift more responsibility onto their workers, the bank said Monday.

Health savings accounts grew by more than a third in 2011, with 50,000 new accounts from existing corporate clients and new relationships with employers and individuals, the bank said. The products are the fastest-growing of the health care finance options the Charlotte bank offers, part of a broader business that provides retirement and benefit plans.

"It comes down to, health care is the No. 1 or 2 financial concern for virtually every customer segment that we have," said Justin Raniszeski, health benefit solutions executive for Bank of America Merrill Lynch.

Large corporate clients are increasingly focused on how expensive health care is to employees, small-business owners are looking at how they can continue providing coverage and, "as employees and consumers, it's top of mind for us as well, in terms of how we afford health care today and in the future," he said.

The bank has been in the business since 2005, Raniszeski said. Now, it has nearly 200,000 health savings account users with more than $300 million in account balances. The average balance has grown more than 10 percent since 2010 to $2,016.

Health savings accounts, designed to work with high-deductible health plans, allow employees to make pretax contributions for medical expenses such as doctor visits and prescriptions. The accounts earn tax-free interest, move with employees when they change jobs or retire and can be carried over year to year. That makes them different from flexible spending accounts, where employees must use the money they set aside by the end of the plan year to avoid losing it.

Bank of America offers the products through its corporate clients and also to individuals and small-business owners who use the accounts outside of the workplace, the bank said.

Kevin Crain, the bank's head of institutional retirement and benefit services, said the accounts have become more popular as employers give more accountability to workers for their financial security, from 401(k)s to health benefit plans.

Health savings accounts fit naturally with the bank's other services, he said, because corporate clients' financial concerns extend beyond just retirement accounts.

They're also becoming more popular as more employees become aware of the benefits, Raniszeski said.

"People are finding they can actually save some money every year in these accounts and start to build a decent-sized balance for future health care costs and even roll it into retirement," he said.

The accounts give employees more control over their spending and can ultimately influence their behavior, too, encouraging smarter lifestyle choices and health spending decisions, Raniszeski said.

"The reason we're excited about it is, I don't think we see those things changing," he said.