A requirement to take certain amounts of money out of IRAs after the account holder passes age 70 ½ accounts for much of the withdrawal activity, according to the Employee Benefit Research Institute.

Just over 22 percent of those who have an IRA took a withdrawal in 2013, it said, which was largely driven by the IRS rule to take required minimum distributions beyond reaching that age. In contrast, only 10 percent of account holders under age 60 took out money.

Of those required to take distributions all but a quarter took only the minimum required, which suggests most are taking out money at rates that “appear to be sustainable” throughout the person’s lifetime—in other words, that the person will not deplete the account too soon.

The report also looked at one group of investors over time and found, not surprisingly, that the percentage of individuals within that group making withdrawals increased as they aged.