Sleep is a recurring natural state of mind and body characterised by reduced consciousness, reduced sensory activity and perception, reduced muscle activity (increased muscle relaxation) and consequently reduced interactions with the surroundings.
Sleep is essential for all animals and is when the body builds up, restores energy and every other system (muscular, nervous, endocrine and immune systems) during this period of rest. Inadequate quantity and quality of sleep can lead to a variety of diseases including diabetes, heart disease, strokes, obesity and depression and other psychiatric disorders.
Modern living with long working hours, working through the night, travelling through various time zones, use of various electronic gadgets (Blue light emitted by mobile phones tablets and laptops supposedly inhibit the release of the sleep hormone melatonin) disrupt normal sleep and lead to typical stress related disorders.
While each person requires different amounts of sleep, on an average a 40 yr old needs 7 hr every night, 6 1/2 hrs of sleep at ages 45-60 and about 6 hrs or less at the age of 80 yrs and above.
Sleep occurs in cycles that last 90-110mins (i.e., less than 2 hr). Each cycle has 2 types of sleep, NREM (non rapid eye movement or slow wave sleep) and REM (Rapid eye movement sleep). NREM has 4 stages 1,2,3 &4). When we close our eyes to sleep , we are in stage 1 and we gradually move into the other stages as we continue to sleep. Stages 1 and 2 are the lighter planes of sleep and 3 and 4 are the deeper planes. Throughout each stage the body relaxes progressively and the EEG (brain activity) changes and slows down.
REM sleep deprivation leads to sleep that is not restful. More time is spent in stage 3-4 during the first half of the sleep period. In the second half, more REM sleep happens as shown in the diagram. As REM sleep is most restful, staying awake during this period (between midnight to 4AM) has health consequences. Younger children especially newborns spend much longer times in stage 4 sleep and REM sleep. REM sleep duration reduces with ageing to much less than the 25% enjoyed by young adults.
You may have a sleep disorder if you have trouble falling asleep when you lie down in bed, if you wake up feeling tired and if you tend to doze off during the day especially during work.I had a friend who fell asleep at the wheels of his car and had a serious accident. If these are issues for you, the question may arise if you should buy a smart device to track your sleep. Unfortunately most of these devices that are worn on the wrist are not medically validated to diagnose sleep disorders. Most of them detect body movements or in some cases the heart rate and its variability, to decide if you are asleep or awake. These devices could get fooled into believing that some insomniacs are asleep when they have their eyes closed, body relaxed and are in bed waiting to fall asleep. So while these devices may be accurate in detecting duration of sleep (based on movements etc), they can be quite inaccurate when they calculate the time spent in the different stages of sleep and also when they make assumptions about the quality of sleep. My smart device suggested that I had sleep apnoe when it detected that I woke up 20-25 times during the night. As I didnt have any symptoms of a sleep disorder, I concluded that it probably detected my movements in bed and inferred that I had woken up. The sleep specialist whom I discussed this also came to the same conclusion. On the other hand, validated sleep study devices (Polysomnography) monitor various parametes such as EEG, ECG, Muscle tone, chest and abdominal movememts, O2 saturation and limb movements to give a detailed analysis of sleep. Compared to these devices, sleep trackers are only 78% accurate in detecting sleep vs wakefulness, 38% accurate in identifying exactly how long it took to fall asleep and only about 50% accurate in detecting the various stages of sleep (including REM sleep).
So should you by a sleep tracker? I believe that anything that is measured, improves. Therefore if you aren’t sleeping well, it may be a good idea to buy a sleep tracker. Many of these devices also measure your heart rate during sleep and an increasing RHR (resting heart rate) may also be indicative on a non-restful sleep.
I have used the Samsung Galaxy watch 3 which is excellent for sleep monitoring and the apple watch which is more accurate for heart rate monitoring (especially during exercise). So go ahead and buy a smart watch that can track your sleep, focus on all the things that you need to do to stay healthy and get healthier!