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One-third of Medicare beneficiaries are now enrolled in a Medicare Advantage plan, and that number is expected to grow, according to a new report from the Kaiser Family Foundation. 

Medicare Advantage hit the milestone this year, with 19 million beneficiaries enrolled in an MA plan. Enrollment has increased 71% since the Affordable Care Act was passed in 2010, Tuesday’s Kaiser report shows.

“The trend in enrollment growth is continuing in 2017, and has occurred despite reductions in payments to plans enacted by the Affordable Care Act of 2010,” report authors wrote.

The report notes that MA’s enrollment numbers are expected to grow, with the Congressional Budget Office predicting that 41% of Medicare beneficiaries will be enrolled in the plans by 2027.

The report’s authors also note the increasing number of beneficiaries — many of which could land in long-term care facilities in coming years — will require more oversight from health officials. They also called for increased scrutiny of how provider access, care quality and patient outcomes differ between traditional Medicare beneficiaries and those on MA plans.

“As Medicare Advantage takes on an even larger presence in the Medicare program, careful stewardship and oversight by policymakers is needed to make sure that plans provide value to the Medicare program, and the 57 million beneficiaries it covers.” the report reads.

Over the past year alone, MA has grown by 8%, or 1.4 million, beneficiaries. That statistic signals the growing role MA plans play within the Medicare program, according to the report’s authors. 

The report also breaks down the biggest MA insurance firms by enrollment, with UnitedHealthcare — which recently made headlines for lawsuits claiming it engaged in fraud in its MA plans — leading the pack with 24% of beneficiaries. Humana ranks second, with 17% of beneficiaries.