(HealthDay)—The Affordable Care Act's Marketplaces covered a disproportionate share of non-elderly adults with high health care risks in the 2014 to 2015 time period, according to a study published in the April issue of Health Affairs.

Michael Karpman, from the Urban Institute in Washington, D.C., and colleagues assessed use of private non-group health insurance through federal and state-based Marketplaces among non-elderly adults with from July 2014 to December 2015.

The researchers found that over the study period, 45 percent of Marketplace enrollees aged 18 to 64 years were treated for chronic conditions, compared to 35 percent of non-Marketplace non-group enrollees and 38 percent of adults with employer-sponsored insurance. Compared to other privately insured adults, Marketplace enrollees also had higher service use, which likely contributed to rising premiums in the non-group market.

"As repeal of the ACA individual mandate takes effect in 2019, protecting coverage gains for adults with chronic conditions while stabilizing non-group premiums may depend on state-level efforts to spread the risk of Marketplace enrollees' across a balanced insurance pool," the authors write.