Arkansas and Kentucky have had the biggest reductions of uninsured adults since the Affordable Care Act’s requirement that Americans have health insurance took effect in January, a new poll shows.

By the end of June, 12.4 percent of all adults in Arkansas were without health insurance, a 10.1 percent drop compared the state's 2013 rate of 22.5 percent, say the results of a Gallup poll released Tuesday.

In Kentucky, the rate fell 8.5 percentage points to 11.9 percent, compared with 20.4 percent in 2013.

Arkansas and Kentucky expanded Medicaid coverage since most Obamacare provisions were implemented at the beginning of the year.

Both states are hosting two of the hottest and most contentious Senate races this year.

Republican Senate Majority Leader Mitch McConnell holds a narrow 2.5 percentage-point margin over his likely Democratic challenger, Alison Lundergan Grimes, according to a composite of recent polling done by Real Clear Politics. In Arkansas, GOP challenger Rep. Tom Cotton leads Sen. Mark Pryor by 3 percent points, says Real Clear Politics.

Delaware, Washington and Colorado round the top five states with the the sharpest decline in uninsured rates.

The 10 states that reported the largest declines in uninsured rates all expanded Medicaid and either established a state-based marketplace exchange or a state-federal partnership.

Nationally, 17.3 percent of U.S. adults reported being without health insurance in 2013, a rate that had increased from 14.8 percent in 2008, Gallup says.

The uninsured rate peaked at 18 percent in the third quarter of 2013 — the three months immediately preceding the opening of the health care exchanges — but declined to 13.4 percent in the second quarter of 2014, the lowest quarterly rate in more than six years of Gallup-Healthways Well-Being Index trending.