Patient Rose Bush receives treatment from Dr. Leon Yeh amid the rollout of President Barack Obama's Affordable Care Act in the Emergency Room at OSF Saint Francis Medical Center in Peoria, Illinois, Nov. 26, 2013. Reuters

The number of Americans without health insurance has dropped significantly this year, just months after President Barack Obama's Affordable Care Act extended coverage to millions of people in January. In all, 13 percent of Americans remain uninsured, compared with 16 percent in 2010, according to findings released Tuesday by the Centers for Disease Control and Prevention.

The National Health Interview Survey found 3.8 million more people have health care insurance compared with 2013 after an 8 percent declined in the number of uninsured. Adults between the ages of 18–64 were almost three times as likely as children to be uninsured. People with high school diplomas were more likely to have insurance than those who didn't have a high school education.

Proponents of the so-called Obamacare law say the findings suggest Obama's ongoing health care overhaul has made an immediate difference in the quality of health care in the U.S. But others said it's still too early to tell.

“This is really a three-year process of implementation,” Jonathan Gruber, an economist at Massachusetts Institute of Technology whose work was used in shaping the law, told the New York Times. “Trying to draw strong conclusions from one quarter of one year is impossible.”

Earlier this month, the federal government predicted that the number of uninsured would drop from 45 million in 2012 to 23 million by 2023 because of the Affordable Care Act, according to a report from the Centers for Medicare and Medicaid Services Office of the Actuary.

“Health care costs are increasing at a slower rate thanks to the Affordable Care Act,” Marilyn Tavenner, administrator for the Centers for Medicare and Medicaid Services, said in a statement. “The dramatic decrease in the number of uninsured Americans is a win for our country and its economy in the future.”

Meanwhile, the Obama administration announced Monday that it would stop health insurance for 115,000 people who failed to prove they were legal residents eligible for coverage under the health care law.