New studies are discovering just how vital sleep is to overall health.

So, sleep habits should become a standard part of a complete check-up, researchers say.

"There is increasing evidence that there is a very strong relationship between sleep quality and physical and mental health," said Dr. Phyllis C. Zee, a professor of neurology at Northwestern University's Feinberg School of Medicine.

"If you have poor health, that is associated with poor sleep. Also, if you have poor sleep, there is an association between that and poor health," Zee said. "What we don't have yet is the research to categorically say that if you improve sleep, you will improve conditions, such as diabetes or hypertension, or other medical conditions."

Still, physicians should be asking their patients about the quality and quantity of their sleep, Zee said. "Sleep should be another vital sign," she said.

Zee wrote an editorial in the Sept. 18 issue of the Archives of Internal Medicine, a special, themed issue on sleep and its relationship to overall health.

In one study, led by Richard L. Nahin, a senior advisor for scientific coordination and outreach at the U.S. National Center for Complementary and Alternative Medicine, looked at why people had trouble sleeping and how many were using alternative drugs to help them sleep.

Insomnia and trouble sleeping are most often associated with high blood pressure, heart failure, anxiety and depression, according to a national survey of 31,044 adults. "That's unusual. It had been most often thought that insomnia was quite prevalent on its own, but only 4 percent of the people who said they had insomnia said they had it without any of those conditions," Nahin said.

The researchers also found that 1.6 million Americans are using alternative therapies, such as melatonin to treat their insomnia. "That's quite high when you consider that there is very little reliable data on the efficacy and safety of using the products people are using," Nahin said.

These findings have implications for treating sleep problems, Nahin said.

"Instead of treating the insomnia itself, a health-care provider might be better off treating one of these comorbidities," he said. "In addition, a physician seeing a patient for insomnia should ask if the patient is using any alternative and complementary treatments, because they might upset the treatments the health-care provider wants to apply."

Another study found that people who have sleep-related breathing disorder -- marked by frequent pauses in breathing, labored breathing, or reduced breathing during the night -- were two to 2.6 times more likely to develop depression. Moreover, the odds of depression increased as breathing disorders became more severe, according to researcher Paul E. Peppard and colleagues from the University of Wisconsin.

And a study by French researchers found that people with allergic rhinitis, caused by hay fever and other allergies, have more difficulty sleeping and more sleep disorders than people without allergies. "The results show a significant impact of allergic rhinitis on all dimensions of sleep quality and, consequently, a lower quality of life as reflected by more somnolence [sleepiness]; daytime fatigue and sleepiness; and impaired memory, mood and sexuality, with a significantly increased consumption of alcohol and sedatives in cases compared with the control group," the study authors wrote.

One expert agrees that sleep problems shouldn't be ignored.

"If you think insomnia is an annoyance and merely something you should tough out, that may be a mistake," said Michael L. Perlis, director of the Sleep Research Laboratory at the University of Rochester, in New York. "It may lead you down the path to other morbidities. It would also be a mistake because it's treatable."

Other studies in the same journal issue found that:

• Fewer hours of sleep may contribute to poor health in young adults.
• Those in rural areas who sleep fewer hours appear to weigh more.
• The immune system may play a role in narcolepsy, a disorder characterized by an uncontrollable urge to sleep.
• The immune system may be affected by a lack of sleep that contributes to inflammation and a variety of diseases.

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