THE KIDS HAVE FLOWN the coop and are thriving, so you don’t lie awake anymore wondering what time they’ll be coming home. Even though your retirement portfolio recently took a hit, you’ve stashed away enough money so that you don’t have to worry about your next mortgage payment. Other issues that used to keep you tossing and turning are also resolved. In other words, you’re at a point in life when you should be getting a good night’s sleep. Nonetheless, it’s 4am, and you’re wide awake — for the umpteenth night in a row.

Join the sleepless crowd. More than 60% of adult Americans experience a sleep problem at least a few night’s a week. And it can get worse with each year. After age 50, medical conditions such as back pain, arthritis, and bladder problems begin to take their toll on sleep. Also, specific sleep disorders, such as restless legs and sleep apnea, become more common. But even more fundamental than these physical issues are changes in the very nature of sleep.

Scientists are still in the dark about this question, although various theories have held sway over the years, including both the ebb and flow of hormones and a buildup of carbon dioxide in the body. The latest theory is that sleep restores energy to the brain’s nerve cells, according to Andrew A. Monjan, Ph.D., chief of the National Institute on Aging’s Neurobiology of Aging branch. In other words, sleep is hardly a dormant state; while you’re snoozing away, your brain is busy recharging.

To give the brain a chance to restore itself, the body’s systems first must get it ready to go to sleep. At about 6pm each evening, the pineal gland begins to secrete melatonin, which will gradually build up over the next few hours. At the same time, levels of the molecule adenosine, a breakdown byproduct of normal metabolism, begin to rise. “Once adenosine reaches a certain level, you activate cells that end up producing sleep,” says David White, M.D., professor of sleep medicine at Harvard Medical School.

While the process is more complicated than this, you get the idea. After a round of shuteye, you feel mentally and physically renewed. Skimp on sleep however, and you’re likely to drag during the day. Researchers at the University of Pennsylvania in Philadelphia restricted participants in a recent study to four, or six, or eight hours of sleep each night for 14 nights. By the sixth day, those allowed six hours — an average night’s sleep for many people — were roughly as alert as those who had gone without any sleep for one night. And that’s not very alert.

If chronic sleep deficit becomes your norm, you may be able to execute low-level mental chores such as figuring the tip on your lunch bill — but it may take you longer than it would if you were rested. And you may as well say good night to performing several work tasks concurrently, absorbing new information, or making sound judgment calls, especially in a crisis. All told, “Anything that’s not routine becomes difficult if you’re tired,” Monjan says.

Maybe you’ve heard that you need less sleep as you get older. That’s just wishful thinking. The need for sleep doesn’t diminish in midlife or even in late life. You still require the same amount you did when you were 25 or 30 years old — about eight hours a night.

“Yet the pattern of sleep does change as we age,” says Sonia Ancoli-Israel, Ph.D., director of the sleep disorders clinic at the Veterans Affairs San Diego Healthcare System in California. You may find yourself getting sleepy earlier in the evening, say 8pm instead of 10pm, and routinely waking at 4am instead of 6am. These kinds of changes result from natural shifts in circadian rhythm, the biologic clock all humans carry within themselves that is based on an approximate 24-hour cycle.

However, if you continue to go to bed at 10pm, which has been your routine lights-out time for decades, you’ll still wake at 4am. “That’s morning to your body,” Ancoli-Israel says. But, unfortunately, you’ve only slept for six hours.

How we sleep changes in other ways as we age. During sleep, people go through four distinct phases: Stages 1 and 2, the lightest stages, are followed by stages 3 and 4, also called slow-wave sleep, the deepest and perhaps most restorative phases. These latter two stages occur just before REM (rapid eye movement) sleep, when dreaming occurs. For reasons not yet fully understood, getting older brings with it a change in the proportion of various stages of sleep. Infants and children snooze away as much as 20% of the night in stages 3 and 4. But studies show that older adults spend most of the night slumbering in the lightest stages; deeper stages 3 and 4 sleep may occupy only 5% of the night.

At the same time that sleep patterns change, the incidence of sleep disorders increases. The years after 50 are the prime target for a condition called sleep apnea, a slumber if there ever was one. In sleep apnea, which affects about 4% of middle-aged men and 2% of middle-aged women, tissue in the esophagus momentarily obstructs the airway, causing breathing to stop — sometimes briefly, sometimes for 10 seconds or longer. When oxygen levels plummet, the person wakes up, but perhaps not sufficiently to realize what has happened. According to the National Institutes of Health, someone with sleep apnea may experience as many as 20 to 30 or more involuntary breathing pauses each hour.

Two additional disorders that can interfere with getting a good night’s sleep are restless leg syndrome (RLS) and periodic limb movement disorder (PLMD). In RLS, unpleasant creeping, crawling, and tingling sensations produce the irresistible urge to move the legs, especially at night when you’re lying down waiting to fall asleep. PLMD involves involuntarily kicking several times a night that causes you to hover in lighter stages or wake up. “The majority of patients with RLS also have PLMD,” says Andrew L. Chesson, M.D., Jr., Director of the Sleep Disorders Center and professor of neurobiology at Louisiana State University Health Sciences Center in Shreveport.

The exact causes of the two disorders are still unknown. Sometimes RLS is inherited, and some cases have been associated with nerve damage in the legs as the result of diabetes. A number of scientists believe that the mechanism underlying PLMD involves a problem in the nervous system. Both disorders can be treated with drugs. Other sleep robbers include pain from arthritis, heartburn, low back pain, and medications with side effects that interfere with sleep.

“You know you have a problem if you can’t sleep when you want to or you’re your bedmate tells you your sleep is disrupted,” says David N. Neubauer, M.D., associate director of the Johns Hopkins Sleep Disorders Center in Baltimore.

If any of these symptoms lasts more than a month and interferes with the way you feel and function during the day, seek help from your doctor. The solution may be as simple as switching to a medication that doesn’t cause sleeplessness or treating a medical condition that does. For more complex problems, ask your doctor to recommend a sleep specialist. You don’t have to put up with sleepless nights because that’s just the way it is. “By itself, getting older is not a cause of insomnia,” Monjan says. •

In addition to consulting your doctor, here are some other strategies that can help put you on the road to dreamland:

• Darken your bedroom. If you get up during the night to go to the bathroom, use a nightlight to show the way rather than turning on a bright overhead light.

• Reserve your bed for sleeping. Move the television set into another room and, if possible, limit bedtime reading to a chair next to your bed.

• Avoid caffeine and alcohol. If sleep is really a problem, avoid any caffeine after lunchtime.

• As for alcohol — you may be able to get away with having a glass of wine with dinner and still sleep well. But if you’re having trouble, do without anything alcoholic for a few weeks to see if it makes a difference. As for nightcaps, forget them. Alcohol will make you drowsy initially, then cause you to wake hours later.

• Grab a nap — maybe. For some people, a 15-20 minute midafternoon nap can make all the difference to the rest of the day, but for others, it’s the recipe for lost sleep at night. People suffering from insomnia should avoid naps.

• Exercise. Exercise helps you sleep longer and fall asleep faster. People who exercised generally slept an hour longer each night and also could fall asleep more quickly.

• Get some afternoon light. Spend time outdoors in the afternoon. This can help turn back your circadian clock and counteract the natural aged-related tendency to fall asleep earlier in the evening and wake up earlier in the morning.

• Eat lightly at night. For reasons that are still unclear, a sizeable meal an hour or two before bedtime can interfere with sound sleep. If you eat dinner after 8pm, try to make it a light meal.