Student loan debt hangs over the heads of a fast-growing number of older Americans, according to a report by the Consumer Financial Protection Bureau.

The debts frequently are for loans taken out to finance education for children and grandchildren, but some are leftover from the schooling of the older learners themselves. The debts can cause serious problems for the over-60 set, the bureau says.

The number of Americans age 60 and older with student loan debt has quadrupled over the last decade from 700,000 in 2005 to 2.8 million in 2015. At the same time, the average debt for these people has nearly doubled from $12,100 to $23,500.

“Although most student loan borrowers are young adults between the ages of 18 and 39, consumers age 60 and older are the fastest-growing age segment of the student loan market. This trend is not only the result of borrowers carrying student debt later into life, but also the growing number of parents and grandparents financing their children and grandchildren’s college educations,” the report says.

Twenty-seven percent of older Americans who have student loan debt borrowed the money for their own education, while 73 percent were financing their children’s and grandchildren’s educations.

Older people owing student loans are also likely to have other types of debt. In 2013, for example, 63 percent of older student loan borrowers also owed mortgage debt, 67 percent owed credit card debt and 45 percent owed auto loan debt.

Defaulting on student loan payments can have serious consequences. Thirty-seven percent of federal student loan borrowers age 65 and older were in default in 2015 compared to only 17 percent of borrows age 49 and under.

One of the consequences for older Americans is having their Social Security benefits reduced to pay the debt, which is happening to a growing number of older federal student loan borrowers. The number of borrowers age 65 and older who had their Social Security benefits reduced to pay student loan debts increased from about 8,700 to 40,000 borrowers between 2005 to 2015. The federal government also can garnish a borrower’s wages and take money from tax refunds.

Social Security “benefit offsets may impose serious financial hardship for many of the affected older borrowers,” the bureau says.

The bureau combined data from a number of sources to compile its report.