Seven seems to be the magic number where sleep is concerned; less than that and you get fat and old quickly. Much more and you risk a heart attack.
We are all born with a body clock that is "set" to sleep at night and stay awake during the day. This is called a circadian rhythm and it evolved over hundreds of years to align your physiology with your environment.
Because of the speed of life these days, we don’t often get as much sleep as we need and research is now showing that lack of sound sleep extracts a heavy toll on your health, both mentally and physically.

If you deprive yourself of sleep, or switch your waking/sleeping rhythm (due to working in shifts for example), you send conflicting signals to your body, which can lead to endocrine and metabolic breakdowns, with devastating results.
If you sleep too little your thyroid and stress hormone levels are affected and this in time can lead to:
•    High blood sugar levels: Your sleep starved brain craves starches and sugars as opposed to fruit and veggies. Too much of these can lead to diabetes.
•    Weight gain: Lack of sleep decreases the hormone that tells you when you are full and simultaneously increases the one that makes you feel hungry. So you eat more and more often. How quickly can you say fat suit?
•    Increased cancer risk: When the balance of hormones in your body is altered, you increase your risk of getting cancer. Studies have shown that tumors grow two to three times faster in laboratory animals with severe sleep dysfunctions.
•    If you sleep more than nine hours a night, your risk of cardiovascular disease increases by 50 percent
That said, what IS the ideal amount of sleep?
To some extent, your age and activity level will determine your sleep needs. Children and teens, for instance, need more sleep than adults. However, your sleep needs are individual to you. You may require more or less sleep than someone of the same age, gender and activity level.
Studies suggest that healthy adults have a basal sleep need of seven to eight hours each night, but your individual sleep requirement may be anywhere between six and nine hours of sleep a night.
The best way to find this out is to listen to your body. If you still feel tired when you wake up in the morning, you probably aren't getting sufficient sleep. Be sure to observe how you feel immediately upon awakening as those first few moments will be a truer measure of how your body is feeling.
How to improve your sleep
Determine a set bedtime for yourself, just as you would for a child
Try not to watch TV or use electronics for about an hour prior to going to bed because that stimulates the brain and you are trying to wind down.
Do something that soothes and relaxes your mind like journaling, meditating, or reading a calming or spiritual book.
Sleep early! Some of your body’s systems, particularly the adrenals, do most of their recharging during the hours of 11pm and 1am, so you should try to be asleep during those hours.
If you have a hard time falling asleep, try and eat a high-protein snack several hours before bed. This can provide the L-tryptophan need to produce melatonin and serotonin which help you to sleep.

Additional information from Mercola.com