Are we dealing with the right concept!

Over the decades of research and medical advancement, it is believed that people, who tend to bite on their nails, are people that endure existing stress, or are classified/diagnosed with some psychological discomfort/disorder. But I wonder if this is correct! I have a different idea! Can that be an evolutionary concept to human behavior? For instance, I think this nail biting is rather a way how human body communicate or alerts the person of body’s lack or excess of calcium. It is believed that finger nails contain microelement such as calcium and magnesium. Thus, the person just removing the peaces or chewing them down, would eventually alter (does not matter how minim) the bodily resources of this microelements.
Although, what I just wrote, may not be makeing sense to some people, and sound rather stupid, this analogy is simply a speculation.