The contrast between exposure to daylight and night-time darkness is thought to adjust and maintain this clock, which helps makes sure the body is working as effectively as possible at times of day when maximum alertness is required. Most adults need about 7 to 8 hours of sleep each night. You know you're getting enough sleep if you don't feel sleepy during the day. The amount of sleep you need stays about the same throughout adulthood. However, sleep patterns may change with age. For example, older people may sleep less at night and take naps during the day.

While a good night's rest can regulate your mood and help you cope with the next day's emotional challenges, sleep deprivation does the opposite by excessively boosting the part of the brain most closely connected to depression, anxiety and other psychiatric disorders. Moreover within families, mothers of children with sleep disorders had significantly greater daytime sleepiness than fathers, even though they reported about the same number of hours of sleep per night.

Narcolepsy is a sleep disorder associated with excessive naps, involuntary daytime sleep episodes, disturbed nocturnal sleep and cataplexy (weakness with emotions such as laughter). Narcolepsy affects over 100,000 people in the United States. Sleepiness is a serious cause of social problems, and primary care physicians need to be alert to the possibility of narcolepsy, especially in patients who do not have the relatively easily recognized symptom of cataplexy; according to Mayo Clinic study

Obstructive sleep apnea (OSA) can elevate the risk for high blood pressure, stroke, heart disease, and cognitive problems. Snoring, a symptom of OSA, is a very common condition affecting nearly 40 percent of adults, and is more common among older people.

Previous study suggested that sleeping for more than eight hours a night, snoring and daytime drowsiness was associated with an increased risk for stroke, researchers reported at the American Stroke Association’s. Also it can be explained as daytime nap for long time brought on by OSA may put you more at risk for cardiovascular problems.

Recently (Oct., 2007) result also suggested that those women with more disrupted sleep as characterized by shorter sleep duration and longer wake time during the night, and those with greater napping time as characterized by napping behavior, were at greater risk for poorer neuromuscular performance and poorer daytime function. And most Parkinson's patient who has long time nap attacks that resembles narcoleptic sleep attacks."

A study published in the American heart association found that the risk of high blood pressure was nearly double for people between the ages of 32 and 59 who slept five hours or less each night. However, the increased risk was not found in older people in the study. Even when factors such as napping behavior, depression, physical activity, alcohol and salt consumption, smoking, pulse rate and gender were taken into account, the risk remained the same. It was reduced a little when obesity and diabetes were taken into account.

A study by CNRS, University of Toulouse; shown that both physical activity and working before 6 am or after 10 pm on the previous day were significantly associated with poorer cognitive performance. It is scientifically established that sleep disturbances due to noise can have a short-term impact on daytime function by:
a) Excessive daytime sleepiness
b) Accidents and drowsy driving
c) Impaired neurobehavioral performance and mood.

Severe sleep apnea presents a serious risk of stroke in the elderly, and it can be overlooked because elderly people often live alone. Sleep apnea is two to three times more common in the elderly compared to middle-aged people. However, typical symptoms of sleep apnea, such as loud snoring or excessive naps for long duration, are less prevalent in the elderly compared to middle-aged people.

Alexandros Vgontzas, M.D., associate professor of psychiatry and a psychiatrist The Milton S. Hershey Medical Center explained in a study that light sleep was associated with increased amount of IL-6 (a cytokine proteins that act as regulators in immune function, metabolism and sleep) during the day while a good night's sleep was associated with decreased day time secretion of IL-6 and a good sense of well being. This finding means that good sleep is associated with decreased exposure of tissues to the potentially harmful actions of IL-6 on the cardiovascular system and bones. In addition, this study demonstrated that healthy people with greater amounts of deep sleep are inherently more capable of tolerating sleep loss, possibly avoiding exposure to the potentially harmful effects of increased IL-6 secretion.

Although there are times during the day when we are naturally likely to feel drowsy, in many cases, sleepiness is a sign that something is amiss; evidence is mounting that sleep—even a nap—appears to enhance information processing and learning. New experiments by NIMH grantee Alan Hobson, M.D., Robert Stickgold, Ph.D., and colleagues at Harvard University show that a midday snooze reverses information overload and that a 20 percent overnight improvement in learning a motor skill is largely traceable to a late stage of sleep that some early risers might be missing. Overall, their studies suggest that the brain uses a night's sleep to consolidate the memories of habits, actions and skills learned during the day.

These days, just about anyone who craves a midday snooze can find plenty of encouragement. Advanced age is associated with changes in sleep architecture with increased difficulties in sleep initiation and maintenance. Elderly subjects, who are often retired, also have more opportunities to take naps during the day

• Naps during the day can also reduce excessive daytime sleepiness. A nap can be refreshing, but it's not a substitute for a full night's sleep. If you nap during the day, keep it short — 15 to 30 minutes. Longer naps may interfere with nighttime sleep.
• Greek adults who took regular naps were significantly less likely to die of heart disease than those who didn't in a study published in the Archives of Internal Medicine in February. Working men benefited most. Daytime nap may improve alertness, memory, physical performance and mood. And the new heart disease study adds to research suggesting long-term benefits.
• Fast-living New Yorkers are paying $12 and up to nap at trendy sleep salons, the New York Times reported recently. One company, MetroNaps, sells and rents napping pods — reclining, hooded chairs equipped with dimming lights and noise-blocking headphones — to airports, hospitals and corporations.
• Rest is just as important as exercise. Sleeping 8 to 10 hours per night and taking naps during the day can help you recover from a flare-up more quickly and may even help prevent exacerbations. If your teen is drowsy during the day, a 30-minute nap after school may be refreshing. But too much nap may only make it harder to fall asleep at night.
• Afternoon naps appear to help lower blood pressure, a beneficial effect that does not occur with resting but remaining awake for the same period of time, study findings show. "It is interesting that a large decline in blood pressure occurs during the daytime sleep-onset period only when sleep is expected," Dr. Greg Atkinson told Reuters Health. "When subjects rest in a supine position, the same reduction in blood pressure is not observed," he said.

This blood pressure reduction may be associated with the lower coronary mortality rates seen in Mediterranean and Latin American populations where siestas are common, Atkinson, of Liverpool John Moores University, UK, and colleagues report in The Journal of Applied Physiology.

The investigators assessed cardiovascular function (blood pressure, heart rate, and measurements of blood vessel dilation) while nine healthy volunteers, 34 years of age on average, spent an hour standing quietly; reclining at rest but not sleeping; or reclining to nap. All participants were restricted to 4 hours of sleep on the night prior to each of the sleep laboratory tests.

During the three phases of daytime sleep, the researchers noted significant reductions in blood pressure and heart rate. By contrast, they did not observe changes in cardiovascular function while the participants were standing or reclining at rest.
"Findings show that the greatest decline in blood pressure occurs between lights-off and onset of nap itself," Atkinson told Reuters Health.

During this sleep period, which lasted 9.7 minutes on average, blood pressure decreased, while blood vessel dilation increased by more than 9 percent. “There is little change in blood pressure once a subject is actually asleep," Atkinson noted, and the researchers found minor changes in blood vessel dilation during sleep.

Future research will examine whether siesta takers are more prone to morning activities and if this morning exercise influences subsequent blood pressure responses to an afternoon nap, Atkinson said.

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