Only about half of American workers are confident they'll have enough money to live comfortably in retirement, according to a survey released last week, but that optimism shrinks further when medical expenses are piled on top of basic expenses.

Job insecurity and debt also put future finances on shaky ground, according to a snapshot of attitudes taken in January.

The Employee Benefit Research Institute, in its 2013 Retirement Confidence Survey, says that the percentage of workers who are confident about having enough money for a comfortable retirement has puddled at the overall record low recorded in January 2011.

This year's survey indicates that only 13 percent of workers are very confident and 38 percent are somewhat confident that they'll have enough savings or income for a comfortable retirement.

On the flip side, 21 percent are not too confident, and 28 percent are not at all confident about their abilities to retire without major financial stresses.

When asked in January about their particular fears, those surveyed said health care expenses, job insecurity and lingering debts particularly clouded their retirement confidence.

Those who are "not at all confident" about covering post-retirement medical expenses jumped to 29 percent in January 2013 from 24 percent in January 2012. Similarly, total lack of confidence about covering long-term care expenses jumped to 39 percent from 34 percent.

Unfortunately, "only 46 percent report they and/or their spouse have tried to calculate how much money they will need to have saved by the time they retire so that they can live comfortably in retirement," said Jack VanDerhei, research director at the institute.

Researchers at the Employee Benefit Research Institute said it's also possible that retirement confidence remains shaky because people have become more aware of their need to build personal savings rather than rely on pensions or Social Security.

Aware or not, the survey found some are woefully unprepared. More than 1 in 4 — 28 percent — said they have saved less than $1,000 toward retirement. Nearly 6 in 10 — 57 percent — said the total value of their household savings and investments, excluding the value of their primary home and any defined benefits plans, is less than $25,000.