Younger adults are overrepresented among Americans who have been fined for lacking health insurance, the government says.

So, federal health officials are teaming up with the IRS to get more people under age 35 into plans sold on government-run health exchanges.

The strategy is one of several announced Tuesday as concerns persist that too few young people have bought coverage through the exchanges to balance the cost of older subscribers, who typically use more care.

People under 35 accounted for 30 percent of all taxpayers during 2014 but 45 percent of filers who either paid a penalty or claimed an exemption from the coverage requirement in the federal Affordable Care Act.

"These households will receive targeted notices talking directly to them about health coverage, and the penalty for not having it," said Christen Linke Young, a deputy director at the Centers for Medicare and Medicaid Services (CMS), during a call with reporters Tuesday. "Our data shows talking about the fee increases response rates by 13 percent."

Government officials didn't directly say Tuesday whether the new exchanges lack young people, or whether there's a target for the share of subscribers they would like to see under age 35.

But health insurers including Minnetonka-based UnitedHealthcare have raised concerns in the past year about the risk mix of those buying through the online marketplaces, which were launched under the health law in 2013.

Individual market shrank

In Minnesota, insurers announced earlier this month that the state's individual market, which includes the MNsure exchange, actually got a little smaller during the first quarter of 2016.

The report from the Minnesota Council of Health Plans, the trade group for insurers, hinted that the state's individual market might lack a critical mass of young and healthy subscribers.

About 6 percent of Minnesotans buy on the individual market, which serves those who don't get health insurance from an employer or a government program. It's a segment of the insurance market that was targeted by the health law.

On Tuesday, federal officials said they will use more e-mail messages during this fall's open enrollment period to reach younger adults. Young adults are almost twice as likely as older consumers to enroll because they receive an e-mail message about exchange coverage, said Joshua Peck, the chief marketing officer for CMS.

The government says it will make it easier for health insurance companies to tell 26-year-olds about insurance options as they move off their parents' plans. The health law extended dependent coverage until age 26.

Outreach efforts will feature new public-private partnerships, including discount codes from the ride-sharing service Lyft that people can use to attend open enrollment events.

Christopher Snowbeck • 612-673-4744

Twitter: @chrissnowbeck