A good night's sleep? Apparently it's a pipe dream for many baby boomers.

As the youngest of 76 million boomers move through their 40s, they'll discover what many older Americans already know: The chances of enjoying restful sleep slowly but steadily decrease. The older the adult, the more likely he'll have chronic insomnia, says Andrew Monjan, chief of neurobiology at the National Institute on Aging. Among twentysomethings, only about 1 out of 8 are insomniacs. By ages 50 to 64, it's 1 out of 5. It rises to 1 in 4 after age 65.

But insomnia is only part of the challenge. Snoring and sleep apnea — repeated short episodes of not breathing — also increase with age. About 3 out of 5 adults over 65 have some kind of sleep complaint, national studies show.

Middle-aged and older adults are flocking to sleep-disorder centers. About 85 percent of patients at many centers are older than 45, says Meir Kryger, a sleep expert at University of Manitoba Medical School and author of "A Woman's Guide to Sleep Disorders."

And as baby boomers hit the prime ages for sleep trouble, specialty sleep clinics are mushrooming. Almost 850 have been accredited in the U.S., more than double the number seven years ago, according to the American Academy of Sleep Medicine. "The sleep field is heating up," Monjan says.

AGE NOT A LONE CULPRIT

Aging per se doesn't cause most of the insomnia; it's the health problems and medications that can come with it, says psychologist Sonia Ancoli-Israel, a sleep expert at the University of California-San Diego School of Medicine. Arthritis, angina and prostate enlargement are among many conditions that can make it hard to sleep through the night. Blood pressure medicines, decongestants, cancer drugs and antidepressants also can keep adults awake.

Often the problem develops over many years. Mimi Payne, 57, a business executive in Los Angeles, remembers lying awake until 2 a.m. in her 40s. "I had a husband, kids, pets and a full-time job on my mind," she says. Lung surgery about 10 years ago seemed to worsen her insomnia. And when she stopped taking estrogen, hot flashes made it even tougher to sleep. Now Payne relies on prescription sleeping pills.

She's getting a medical work-up at the UCLA Sleep Disorders Center, including an overnight hospital "sleep study."

"I hope they can figure out why it's so hard for me to fall asleep and stay asleep," she says.

SLEEP-RELATED DISEASES

There's growing evidence that poor sleep can foster diseases that shorten life, says Fred Turek, director of the Center for Sleep and Circadian Biology at Northwestern University School of Medicine. Sleep problems can lead to biological changes that cause weight gain, increase diabetes risk, promote heart disease and worsen depression.

Memory and mental performance also suffer with poor sleep. That's worrisome in older people because sleep-related problems can mimic dementia and might lead to misdiagnosis, Ancoli-Israel says.

There's also pioneering research suggesting sleep loss could impair immune function, possibly hindering older adults' ability to fight off illness.

Not surprisingly, the sleep drug business is booming. Americans spent $2.1 billion on prescription pills last year and bought 600 million over-the-counter sleep tablets, according to IMS Health and ACNeilsen, firms that track sales.

But many medicines widely used for chronic insomnia, including antihistamines and antidepressants, haven't been proven safe and effective for the problem, said a scientific panel convened last month by the National Institutes of Health. Only one prescription drug, Lunesta, is approved by the Food and Drug Administration for long-term use (up to six months), but many others are taken for a long time.