Actually, it was vitamin A that was thought to cause this but has since been shown not to be the case. They originally thought this because nails are mostly made of keratin, and a deficiency of vitamin A leads to 'keratinzation' of the tissues throughout the body - hence, spots in the nails must be a breakdown of the tissues there so... it must be a vitamin A deficiency. But they have since found that it would have to be such a severe deficiency for a prolonged period that this isn't thought to be the cause with fingernails any longer as people here in the states usually don't have deficiencies of vitamins to that extent as we always consume at least enough to 'get by' even without the use of supplements.
It has since been written that they are simply air pockets and are nothing to worry about. I take a beta carotene supplement and still had them, so I guess I've proved it to myself that I'm ok....and so are you