On a positive note, fewer Americans were uninsured in 2013 than in 2010 -- 14.4 percent versus 16 percent, respectively.
But sharp coverage gaps remained depending on factors like age, race or ethnicity and where people live.
The reports, released Thursday by the U.S. National Center for Health Statistics (NCHS), draw on data from interviews with more than 104,000 families as part of the 2013 National Health Interview Survey. Estimates for 2013 were compared with prior periods going back as far as 1997.
"I think what this gives us is a great baseline," said Shana Lavarreda, director of health insurance studies at the University of California, Los Angeles' Center for Health Policy Research. She was not involved with the studies.
Researchers will use the data to evaluate changes between 2013 and 2014, when millions of previously uninsured Americans will have gained coverage through the Affordable Care Act, also known as Obamacare.
More than 8 million people signed up for private health plans for 2014 under the Affordable Care Act, the U.S. Department of Health and Human Services (HHS) reported in May.
Another 4.8 million enrolled in Medicaid and the Children's Health Insurance Program. And an estimated 5 million people selected health plans sold outside of the new state and federal marketplaces, HHS said.
Because new marketplace options and expanded state Medicaid coverage took effect this year, the increase in coverage was not reflected in the 2013 data.
In 2013, 20.4 percent of people aged 18 to 64 -- the health-reform law's target population -- were uninsured for at least part of the year. They were twice as likely to experience a lack of coverage as children.
Hispanic people were three times as likely, and blacks were more than 1.5 times as likely, to be uninsured as whites, researchers found.
Rates of coverage varied by state as well.
"For example, 3.8 percent and 5.2 percent were uninsured in the District of Columbia and Massachusetts, respectively, whereas 24.8 percent were uninsured in Nevada and 24.7 percent were uninsured in Florida," NCHS statisticians wrote.
In states that are not expanding Medicaid coverage, "state differences in uninsurance may well become even greater," said Katherine Hempstead, team director and senior program officer at the Robert Wood Johnson Foundation in Princeton, N.J.
A majority of adults -- 64.2 percent -- had private health insurance coverage in 2013.
Of those who get health coverage on the job, nearly one-third (32 percent) were enrolled in a high-deductible health plan, compared with 17 percent in 2008.
"This is a near doubling in a period of less than 10 years," Hempstead noted. "This is clearly becoming the new norm, and the marketplace plans will only increase the rapidity of this trend," she added.
Among other findings in the reports:
- Asthma prevalence among people of all ages dropped to 7.4 percent in 2013 from 8.6 percent in 2010 and 2011.
- Twenty-nine percent of adults aged 20 and older were obese in 2013, versus 19.4 percent in 1997.
- Among adults 18 and older, 9.3 percent had been diagnosed with diabetes, compared with 9.1 percent in 2012 and 5.1 percent in 1997.
Will the Affordable Care Act address these disparities?
"What public health researchers are hoping to see . . . is how this humongous growth in health insurance translated not only to access to care, but better health outcomes," Lavarreda said.
Learn about health insurance coverage options under the Affordable Care Act at HealthCare.gov.