Sleep is one of the most important activities that we enjoy a lot. On an average, we spend about one-third of our lives sleeping (assuming one sleeps about 8 hours a day). So, if one's job/profession is important (which also occupies about 8 hours per day), sleep is equally important, if not more!
What is the normal sleep duration?
Normal sleep ranges from 5 to 9 hours per day. Those who sleep less than 5 hours or more than 9 hours per day, have a higher incidence of heart attack, brain stroke, cancer and death.
When is the best time to sleep?
Night is the time meant for normal sleep. This is because the sleep-inducing hormone, melatonin, is secreted only during nights. The secretion of melatonin is inhibited by light, hence, darkness in the bedroom is essential for sound sleep.
Based on the sleep-pattern, there are two types:
1. "Owl" type: Person sleeps late (11 PM-12 midnight) and wakes up late (7AM-8 AM)
2. "Lark" type: Person sleeps early (8 PM-9 PM) and wakes up early (4 AM-5 AM)
These patterns are genetically determined and hence, it is difficult to change them.
Are daytime naps good?
Most of us feel sleepy in the afternoon, especially after a good lunch. However, it is not a good habit to sleep in the afternoon. Between the ages 10 and 60, sleep is monophasic, which means, sleeping only once (at night) is enough. Infants and small children have polyphasic sleep, which means, they wake up and sleep several times in 24 hours. Preschool children and elderly have biphasic sleep, and they require an afternoon nap in addition to night sleep. For others, afternoon nap is not necessary. However, a very short snooze (20 min or so) can be very energizing, especially in those who have to work very hard in the post-lunch session. Sleeping more than 30 minutes in the afternoon may make one very groggy and difficult to concentrate in work.
Why do we need to sleep?
Sleep serves may important functions, some of them are:
1. Makes us feel fresh, and restores the energy.
2. Consolidation of memory happens during sleep. Brain decides what is important and that gets stored in long-term memory. Whatever is un-importnat is deleted from brain storage. So, lack of night sleep can lead to poor memory functions.
3. Growth hormone secretion occurs at night, so, sleep is important for proper growth.
4. Dreams occur during sleep, which is important for normal human functioning. We shall discuss more about dreams separately.
5. Normal night sleep decreases the risk of cancer. This is because melatonin secreted during sleep is an antioxidant and has anti-cancer properties.
Sleep is therefore one of the most important funcitons of human brain, and those with a good sleep are truly blessed!
Dr Sudhir Kumar MD DM
Apollo Hospitals, Hyderabad, India