Can lying in bed, unable to sleep, lead to cancer? You bet it can! Here's a great video on melatonin's role in cancer prevention:
Not only does melatonin inhibit the proliferation of many different types of cancer cells, it also interferes with the blood supply for new growing tumors. The hormone's benefits don't just stop with hindering cancer; it is also a powerful anti-oxidant that helps to fight inflammation. Also, since melatonin protects white blood cells against radiation damage, they provide a boost for the immune system.
Here's a wide list of the studies done on melatonin: List. I'm going through them to sieve out the interesting ones.
Should You Take Melatonin Supplements?
Given the wide range of health benefits of melatonin and the diseases it impacts, should you take a melatonin supplement? It is much more beneficial to have your own body produce the melatonin it needs, using the natural hormonal feedback loops to produce just the right amount for you.
However, if for some reason you find yourself unable to naturally increase your melatonin production and lie awake in bed all night, then it would be wise to consider a melatonin supplement. Only a small amount is needed each night - 0.3mg to 0.5 mg.