More than half of the participants in 401(k) retirement plans at Vanguard now hold a target-date fund, according to a new Vanguard study released Tuesday.

According to the study, Target Date Fund Adoption in 2013, 55 percent of participants in defined-contribution retirement plans at Vanguard held target-date funds. Eighty-six percent of the Vanguard retirement plans offer a target date fund, and target-date funds account for one-third of total plan contributions.

The growing popularity of target-date funds has had a profound affect on the level of risk many participants take with their plan investments, Vanguard says. For instance, in 2013, 10 percent of “do-it-yourself” investors held no equities and 13 percent had only equities. Ten years ago, 13 percent had no equities and 22 percent were entirely invested in equities.

“Target-date funds continue to reshape investment patterns in DC plans in fundamental ways. These funds provide appropriate levels of risk as a participant ages and a remedy to the problem of extreme asset allocations,” says Jean Young, author of the report and a senior analyst in Vanguard’s Center for Retirement Research.

Thirty-one percent of all Vanguard participants held a single target-date fund in 2013, more than double the figure from five years earlier. Among participants entering a plan for the first time, two-thirds were invested in a single target date fund.

A major factor influencing the rise of these funds is their use as a default investment in automatic enrollment plans, in which companies sponsoring workplace retirement plans automatically put employees into their plans and invest their accounts in target date funds, Vanguard says. By the end of 2013, 34 percent of Vanguard plans, covering nearly 60 percent of participants, had adopted automatic enrollment, typically for participants newly eligible for the plans.