U.S. seniors with mental health needs may not have much access to psychiatrists who could help them, new research shows.

Despite an overall heightened demand for mental health services, nearly two-thirds of Medicare Advantage psychiatrist networks included less than 25% of all psychiatrists in a given service area.

"This means that many people who have coverage through Medicare Advantage plans may not actually have access to psychiatrists, given how few are considered in-network," said lead study author Dr. Jane Zhu, an assistant professor of medicine in the School of Medicine at Oregon Health & Science University.

And that data may not fully reveal the extent of the limitations.

Even when a psychiatrist is in-network, that doesn't mean they aren't already fully booked and not taking new patients, Zhu said, since the United States has a shortage of psychiatrists.

"It's likely a rosier picture than reality," Zhu said in a university news release. "We know the actual number of psychiatrists available to see patients is much lower."

In some areas, not even one psychiatrist who accepted Medicare Advantage patients was taking new patients.

The effect on patients is that they may have to pay higher out-of-pocket costs, experience delays in care or not get the care they need at all, Zhu said.

"More than half of the counties for which we had data did not have a single [Medicare Advantage]-participating psychiatrist," the authors wrote in their study. "Our findings offer upper-bound estimates of network breadth, raising concerns about MA enrollees' access to mental health services amid the growing prevalence of mental health conditions among older adults."

Medicare provides health insurance for people 65 and up. Medicare Advantage covers 28 million Americans through private insurance plans backed by Medicare.

These findings suggest it's necessary for insurers to incentivize more psychiatrists and mental health professionals to accept health insurance, Zhu said. Another option would be to expand coverage of services delivered by other health care professionals such as psychologists, counselors or primary care physicians who provide mental health care.

The findings were published in the July issue of the journal Health Affairs. The research was supported by the U.S. National Institute of Mental Health, the Agency for Healthcare Research and Quality and the U.S. National Institute on Drug Abuse.