In 2007, about 3.4 million Americans enrolled in the Medicare Part D drug plan reached a gap in their prescription coverage known as the “doughnut hole,” leading some of them to stop taking prescribed drugs, says a Kaiser Family Foundation study released Thursday.The analysis of data found that 26 percent of Part D enrollees who filled any prescriptions in 2007 reached the coverage gap. This includes 22 percent who were stuck in the gap for the remainder of the year and 4 percent who eventually received catastrophic coverage.

When they applied this estimate to the all Part D enrollees, the study authors concluded that last year about 3.4 million beneficiaries (14 percent of all Part D enrollees) reached the coverage gap and faced paying full cost for their prescriptions.

Enrollees prescribed drugs for serious chronic conditions had a much higher risk of a gap in coverage under the Part D plan. For example, 64 percent of enrollees taking medications for Alzheimer’s disease reached the coverage gap, along with 51 percent of those taking oral anti-diabetic medications and 45 percent of those taking antidepressants.

The data analysis didn’t include beneficiaries who receive low-income subsidies, because they don’t face a gap in coverage under their Medicare drug plan.