Hey Nonya, I googled it and it does seem to be a common question.

The best answer I found is that the smell is a concentration of ammonia built up in the system due to dehydration and/or lack of sleep. It suggested to also to be extra vigilant about hygiene.

It does seem to reason that any chemical in the body will alter a persons smell.

I once knew a guy who was so into health and fitness, he was constantly taking supplements. I noticed he always smelled like a vitamin. Good looking guy, but he brought back memories of the nasty green vitamins my mom used to give us when I was a kid. LOL!