(Bloomberg News) Savers who kept money in their 401(k) retirement plans saw average account balances rise 32% last year, said a study by the Employee Benefit Research Institute and the Investment Company Institute.

Workers who have had money in their 401(k) savings accounts from 2003 and have been with the same plans had average account balances of $109,723 in 2009 compared with $83,161 a year earlier, according to the report released today by the Washington-based organizations. The Standard & Poor's 500 Index rose by about 23% in 2009 after falling 38% in 2008.

"Retirement savers, by continuing to invest paycheck by paycheck, saw the benefits of being in the market in 2009, as stock values generally climbed during the year," Sarah Holden, senior director of retirement and investor research for ICI, a mutual-fund trade group, said in a statement.

The study looked at 4.3 million so-called consistent participants. The report didn't break down how much contributions or investment returns led to larger account balances. EBRI, a nonprofit, and ICI have a total database of almost 21 million participants in 51,852 plans holding $1.21 trillion in assets.

Twenty-one percent of 401(k) savers in plans with a loan option had loans outstanding, up from 18% at the end of 2008 and 2007. The average loan amount was $7,346 in 2009, the report said. Almost 90% of participants had plans offering loans.

The number of people borrowing from their retirement- savings plans reached a 10-year high in the second quarter of 2010, according to Fidelity Investments. Accounts with loans outstanding rose to 22% by the end of June from 20% a year earlier, the Boston-based asset manager said in a study released in August.