The white spots in our fingernails that we probably settle with 'oh, it's just a calcium deficiency', have actually nothing to do with calcium deficiency.
According to SciShow, these milk spots are actually formed when the nail bed forms damaged cells after it experiences a knock or a bump. These little white spots usually move up and disappear after a point of time as the nail grows.
However, in some cases, their presence may indicate a fungal nail infection or even feverish illness. Also, if you have consistent, repetitive white lines running parallel to your nail bed on all your nails, it could be a case of lead poisoning.