Observers say there could be several reasons why Hillary Clinton — the biggest supporter of the Affordable Care Act among all presidential contenders — mentioned health care only once in her acceptance speech.

“Twenty million more Americans with health insurance. … That's real progress,” Mrs. Clinton said, in her sole ACA-related comment last week when she accepted the Democratic Party's presidential nomination.

Her campaign position paper described the ACA as a “critically important step toward the goal of universal health care,” saying it needed changes include reducing health plans' out-of-pocket limits, adding a federal option in public exchanges and pushing states to reduce their Medicaid enrollment income eligibility requirements.

She also has backed lowering the Medicare eligibility age to 55 from 65.

While her health care comments at the Democratic Party's convention in Philadelphia may have been brief, benefit experts say there were several reasons, none of which are due to a diminished interest in health care.

“She may have felt there were more pressing issues and that it was not necessary to discuss health care issues given her long history in backing health care reform,” said Steve Wojcik, vice president of public policy at the National Business Group on Health in Washington.

Another possible reason: Mrs. Clinton's concern about bringing out differences between herself and Sen. Bernie Sanders, I-Vt., her chief rival for the Democratic nod and a strong believer in a Canadian-style national health insurance system.

“She did not want to alienate Sanders' supporters by highlighting their differences” on health care issues, said Allison Klausner, a principal and government relations leader at Xerox HR Services in Washington.

Others say Mrs. Clinton may have felt discussing her stance would have accomplished little.

“She was the only candidate throughout the primaries supporting the ACA. The Republicans all called for its repeal, and Sen. Sanders advocates Medicare for all. So she may have felt that touting her support for the law to the national television audience had limited value,” said James Klein president of the American Benefits Council in Washington.

Mrs. Clinton stressed a “stronger together theme that wouldn't have been helped much by talking about the ACA given how divisive the law still is — even within the parties,” said Geoff Manville, a principal with Mercer L.L.C. in Washington.