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I've seen on a lot of websites that nail-biting behaviour is due to lack of iron in the blood. I'm wondering if is this actually true, or just an urban myth which has spread and spread?

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Can you provide a link to one that makes such a claim? – fred May 19 '11 at 17:57
Funny :) Since I know at least one anecdotal case where this is true, I'd love to see this answered :) – Lagerbaer May 19 '11 at 17:58
I bite my nails when I'm stressed (to a point that I haven't used nail clippers in many years). I was told the same thing that nail-biting indicates an iron deficiency, but I doubt it because I take vitamins and minerals supplements regularly. – Alexandru May 19 '11 at 18:21
Exactly. I bite my own nails as well, but doubt that I have iron deficiency. – Chris Dennett May 20 '11 at 0:16
So far, all I've found is indications, as mentioned by NonSequitor below, that an iron deficiency can cause unusual nail appearance and the occasional mention that fingernail biting could be considered a symptom of pica, which sometimes stems from deficiencies. – Sean Duggan Jun 20 '14 at 18:58
up vote 12 down vote accepted

There are two manifestations of iron deficiency that could explain this claim: koilonychia and pica.

Koilonychia or "spoon nails" is when the nail becomes concave. It can be a classic sign of iron deficiency on physical exam.* The nails of iron-deficient patients may also become brittle and/or split lengthwise.


Some form of pica is present in about half of cases of iron deficiency. It describes a broad range of eating disorders, often associated with mineral deficiencies, where a person will compulsively eat or chew on an unusual substance. Common examples are ice, clay, laundry starch, hair, and the classic, lead paint chips. However nailbiting itself has not been classified as a form of pica, possibly because it's so common among people without any nutritional deficit. Nailbiting (fancy medical word: onychophagia) is overwhelmingly attributed to anxiety, general compulsive behavior, or just being a kid.

So it's not inconceivable that an iron-deficient person with a tendency to put unusual things in their mouth and brittle, misshapen nails might start chewing on them. But it would be a fairly useless diagnostic sign because nailbiting due to other causes is so common.

*Koilonychia, like many "classic" signs, may be more common on med school exams than in real life.

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Sounds feasible :) – Chris Dennett May 20 '11 at 0:02
"Koilonychia, like many "classic" signs, may be more common on med school exams than in real life".It is.Chances are if we're looking at the fingers for anemia, we're not looking at the nail,but at the other side of the finger to do a finger stick test.Much quicker,much more reliable,and a good manicurist can't cover it up.I'll be honest,if someone comes in with fingernails all chewed off,my index of suspicion bypasses anxiety and goes straight to meth,but anyway...All in all +1 for the logic of coming up with a plausible,if unlikely,mechanism to explain this.Good work. – Monkey Tuesday May 20 '11 at 1:01

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