Here people used to say that if someone has large lunula, then s/he is suffering from the deficiency of calcium. After searching the internet I found this: Abnormally large lunula (the white half-moon shape at the base of the nail) suggests an overactive thyroid, while the absence of a lunula can mean an under-active thyroid. The thyroid produces the hormone calcitonin, which plays a role in calcium homeostasis. Please read the following paragraph: Primarily calcium is regulated by the actions of Vitamin D, parathyroid hormone and calcitonin. The only real regulatory organ is the parathyroid gland. The parathyroid glands are located behind the thyroid, and produce parathyroid hormone in response to low calcium levels. The parafollicular cells of the thyroid produce calcitonin in response to high calcium levels, but its significance is much smaller than that of PTH. Don't you think overactive thyroid will produce large quantities of calcitonin which will in turn suppress the level of calcium in body? If this is correct, then those people are correct.