The country’s retirement savings deficit, estimated by the nonprofit Employee Benefit Research Institute at more than $4 trillion, invariably calls into question the matter of 401(k) loans and the extent of the toll that plan leakage may be having on Americans’ ability to save adequately for retirement.

A recent study shows that toll may be much higher than previously thought.

A team of academics affiliated with the Pension Research Council at the University of Pennsylvania’s Wharton School of Business estimates that defaults on plan loans are costing retirement savers $6 billion annually, according to data published in  “Borrowing from the Future: 401(k) Plan Loans and Defaults.”

That’s considerably more than figures published by the Government Accountability Office, which in 2009 put the cost of loan defaults at less than $600 million annually.

While the Department of Treasury limits how much participants can borrow from their savings—not more than half an account’s value, with a $50,000 cap—and the tax penalties for not repaying loans, plan sponsors have the authority to limit how many loans can be taken, or even whether participants can borrow from their savings at all.

The GAO and others have looked at how plan loan activity relates to participant demographics, but the new study out of Wharton claims to be the first to examine how sponsors’ loan policies affect participant behavior.

The findings suggest that how sponsors and their advisors structure loan policy influences how frequently participants access their retirement accounts.

Prohibiting loans is not a tactic many sponsors deploy; 90 percent of active participants in 401(k) plans can access their accounts for loans.

But not all sponsors take the same approach to loans. About 40 percent of the plans that the researchers looked at allowed at least two loans to be taken out at the same time, and more than 50 percent of participants were in such plans.

In measuring the loan activity and default rates of participants in multiple-loan plans versus those whose plans allowed only one loan at a time, the researchers found that participants with access to more than one loan were twice as likely to borrow from their accounts. And the aggregate borrowed was 16 percent higher in plans that allow multiple loans.

That’s troubling to the paper’s authors because it suggests participants may be viewing the multiple-loan option as an endorsement by their employer to go ahead and borrow from their retirement savings.

About 20 percent of participants had outstanding 401(k) loans in 2012, according to EBRI, a level that has been constant since then.

Depending on the economic conditions in any given year, that can mean plan leakage accounts for between 30 and 45 percent of total annual contributions.

Most loans are paid back on time, with interest that accounts for retirement savings that may have been lost while the loan was out.