WASHINGTON - Getting older doesn't just mean a risk for physical ailments like heart disease and bum knees: A new report finds as many as 1 in 5 seniors has a mental health or substance abuse problem.

And as the population rapidly ages over the next two decades, millions of baby boomers may have a hard time finding care and services for mental health problems such as depression - because the nation is woefully lacking in doctors, nurses and other health workers trained for their special needs, the Institute of Medicine said Tuesday.

Instead, the country is focused mostly on preparing for the physical health needs of what has been called the silver tsunami.

"The burden of mental illness and substance abuse disorders in older adults in the United States borders on a crisis," wrote Dr. Dan Blazer of Duke University, who chaired the Institute of Medicine panel that investigated the issue. "Yet this crisis is largely hidden from the public and many of those who develop policy and programs to care for older people."

Already, at least 5.6 million to 8 million Americans age 65 and older have a mental health condition or substance abuse disorder, the report found - calling that a conservative estimate that doesn't include a number of disorders. Depressive disorders and psychiatric symptoms related to dementia are the most common.

While the panel couldn't make precise projections, those numbers are sure to grow as the number of seniors nearly doubles by 2030, said report co-author Dr. Peter Rabins, a psychiatrist at Johns Hopkins University. How much substance abuse treatment for seniors will be needed is a particular question, as rates of illegal drug use are higher in boomers currently in their 50s than in previous generations.

Mental health experts welcomed the report.

"This is a wake-up call for many reasons," said Dr. Ken Duckworth of the National Alliance on Mental Illness. The coming need for geriatric mental health care "is quite profound for us as a nation, and something we need to attend to urgently," he said.

Merely getting older doesn't make mental health problems more likely to occur, Rabins said, noting that middle age is the most common time for onset of depression.

But when they do occur in older adults, the report found that they're too often overlooked and tend to be more complex. Among the reasons:

• People over 65 almost always have physical health problems at the same time that can mask or distract from the mental health needs. The physical illnesses, and medications used for them, also can complicate treatment. For example, up to a third of people who require long-term steroid treatment develop mood problems that may require someone knowledgeable about both the medical and mental health issues to determine whether it's best to cut back the steroids or add an antidepressant, Rabins said.

On the other side, older adults with untreated depression are less likely to have their diabetes, high blood pressure and other physical conditions under control - and consequently wind up costing a lot more to treat.

• Age alters how people's bodies metabolize alcohol and drugs, including prescription drugs. That can increase the risk of dangerous overdoses, and worsen or even trigger substance abuse problems.

• Grief is common in old age as spouses, other relatives and friends die. It may be difficult to distinguish between grief and major depression.

That also means a loss of the support systems that earlier in life could have helped people better recover from a mental health problem, said Dr. Paul D.S. Kirwin, president of the American Association for Geriatric Psychiatry. Adding stress may be loss of a professional identity with retirement, and the role reversal that happens when children start taking care of older parents.

"There'll never be enough geriatric psychiatrists or geriatric medicine specialists to take care of this huge wave of people that are aging," Kirwin said.

The Institute of Medicine report recognizes that. It says all health workers who see older patients - including primary care physicians, nurses, physicians' assistants and social workers - need some training to recognize the signs of geriatric mental health problems and provide at least basic care. To get there, it called for changes in how Medicare and Medicaid pay for mental health services, stricter licensing requirements for health workers, and for the government to fund appropriate training programs.