For the first time in many years, the government reported that spending on health care last year grew more slowly than the economy overall. WASHINGTON — The burdensome costs of medical care, prescription drugs and health insurance have become dominant issues in the 2020 presidential campaign. But a new report from the Department of Health and Human Services shows the nation remains in a period of relatively slow growth in health spending. Health spending in the United States rose by 4.6 percent to $3.6 trillion in 2018 — accounting for 17.7 percent of the economy — compared to a growth rate of 4.2 percent in 2017. Federal officials said the slight acceleration was largely the result of reinstating a tax on health insurers that the Affordable Care Act imposed but Congress had suspended for a year in 2017. Faster growth in medical prices and prescription drug spending were also factors, they said, but comparatively minor. For decades, national health spending galloped ahead of spending in the overall economy, lowering wages and stressing household budgets. But over the last decade, the pattern has shifted somewhat. Although the country consistently spends more on health care each year than it did the year before, the overall rate of growth has stayed below historical averages. In 2018, health spending grew more slowly than the economy overall, a rare occurrence. The factors leading to the slowdown are not fully understood. For years, economists thought they were the result of lagging effects of the recession. But as the pattern has continued far into the economic recovery, they increasingly point to changes in the delivery of health care itself.