The number of Americans without health insurance increased again in 2018, the second consecutive year that figure has risen after several years of declines under Obamacare, a Centers for Disease Control and Prevention survey shows.

About 30.4 million Americans did not have health insurance in 2018, up from 29.3 million in 2017, according to the CDC's National Health Interview Survey. That means about 1.1 million more Americans lost insurance coverage last year.

Efforts by the Trump administration and Congress to challenge and loosen requirements of the Affordable Care Act probably played a role in some going without coverage, analysts said.

"I don't think it's too shocking with efforts to undermine the Affordable Care Act as part of the Tax Cuts and Jobs Act," said Daniel Derksen, a University of Arizona professor and health policy expert.

The Tax Cuts and Jobs Act of 2017 eliminated the health care law's individual mandate that required people to get health insurance or pay a penalty. It formed the legal basis for a coalition of Republican-led states to argue in federal court that the entire health law should be tossed out – a challenge the Trump administration supports.

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Derksen said a strong economy means more low-income people probably moved from Medicaid coverage to health insurance through a job. That won't necessarily make health care more affordable for those whose health plans shift costs to them through higher deductibles and co-payments.

The CDC survey says the number of Americans in high-deductible plans reached an all-time high, covering 45.8% of people with private health insurance in 2018. In 2010, 25% of people with private coverage had high-deductible plans.

A Gallup survey found that Americans borrowed $88 billion to pay for health care last year, and one in four people skipped care because of cost.

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High-deductible plans are popular among companies seeking to defray the spiraling cost of health care. A survey by Kaiser Family Foundation and the Los Angeles Times found that many employees in high-deductible plans postponed care or cut spending on household expenses such as food and clothing.

"Employees are taking on more and more of the burden of health care costs," said Cynthia Cox, Kaiser Family Foundation's director of health reform and private insurance. "We might be reaching a breaking point. At some point, employers won’t be able to raise deductibles higher and higher."

The CDC survey is based on data from 72,762 people who were asked whether they were insured.

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The uninsured rate among U.S. working-age adults was 13.3% in 2018, up from 12.8% in 2017. Among all ages, the uninsured rate was 9.4%, but that figure includes seniors on Medicare and children with Children's Health Insurance Program coverage.

Among 17 states with figures reported in the survey, Texas had the highest uninsured rate among working-age adults, 25%, and Massachusetts the lowest, 4.9%.

The CDC survey followed a Congressional Budget Office report last month that found a similar decline in health coverage after years of gains under the Affordable Care Act.