(Washington Post illustration; iStock)

Health spending in the U.S. grew to $3.2 trillion in 2015, fueled partly by the expansion of health insurance to millions of people under the Affordable Care Act, according to a new estimate published in the journal Health Affairs.

The study also looks forward, projecting that through the next decade, national health spending will climb at 5.8 percent per year, on average, to encompass a fifth of the economy by 2025.

The report, compiled by a team of government actuaries, shows overall health spending picking up after a historic slowdown, but the growth remains lower than the nearly 8 percent annual growth in the two decades before the Great Recession. 

The Obama administration — including the president himself in a recent essay — has credited the Affordable Care Act with keeping health expenditures in check. But economists remain uncertain whether the slowdown in spending is because of provisions of the law or might be explained by other factors.

In a statement, Andy Slavitt, the acting administrator of the Centers for Medicare and Medicaid Services, pointed to the health care law's role in tempering growth: "The Affordable Care Act continues to help keep overall health spending growth at a modest level and at a lower growth rate than the previous two decades," he said.

But a recent editorial by two economists published in the Journal of the American Medical Association was skeptical of the idea the law could be credited with the slowdown in the growth of spending — and noted an array of future challenges.

"This pressure on health care cost increases is not likely to moderate. Experts expect a wave of new medicines and devices, including immunotherapies in oncology, breakthrough treatments for Alzheimer's disease, and new gene and cell therapies. Each treatment offers great promise but is likely to further accelerate health care spending," Amitabh Chandra of Harvard University and Jonathan Skinner of Dartmouth College wrote in the Journal of the American Medical Association.

Katherine Hempstead of the Robert Wood Johnson Foundation recently wrote a commentary arguing that even a slower rate of growth could pose difficult choices.

"Even under the rather optimistic assumption that health care spending grow no more quickly than the economy itself; we will, before long, be forced to choose between an unpleasant combination of significant tax increases and/or cuts in defense and non-health spending," Hempstead wrote.

The study notes a few trends that are about to change: Growth in the out-of-pocket costs borne by consumers slowed over the last few years as uninsured people gained coverage and was projected to pick up again — reaching 5.5 percent annual growth between 2020 and 2025. Despite the growth, out-of-pocket costs will actually represent a slightly lower portion of overall health spending in 2025 than in 2014.

And prescription drug spending, which spiked in recent years due in part to the introduction of effective but expensive treatments for hepatitis C beginning in late 2013, was projected to return to more moderate growth — with an average annual growth rate of 6.7 percent for 2016 through 2025.

There are uncertainties to any estimates of future spending, but the new analysis suggested that economic growth, inflation of prices for medical services and products and the aging population would be the major drivers of spending increases.

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