As already mentioned, the body is complex and it is often times difficult to nail a problem or a symptom down to one specific missing mineral or trace element. Since many nutrients and minerals, herbs etc. work together, it is often hard to find the missing pieces of the puzzle.
For example if your are looking up thinning hair, dry skin and brittle nails, parts of the puzzle MAY include Biotin, Calcium, Maganese, Selenium, Copper, Iron and Iodine. We should not just start taking mega doses of one or more of these elements as they need to work together in perfect harmony and taking too much of one or (NOT enough) can throw the others out of whack.
King James Bible (Cambridge Ed.) Genesis 2:7
And the LORD God formed man of the dust of the ground, and breathed into his nostrils the breath of life; and man became a living soul.
This web site is a good read and a good reference LINK:
I will post an excerpt for iodine, however suggest you look at all of these :
Iodine | More on Iodine
Deficiency of iodine may also result in brittle fingernails or brittle toenails indirectly, as it causes hypothyroidism (under-production of thyroid hormones) which can lead to symptoms such as dry brittle hair, hair loss, brittle nails, coarse dry pale skin, intolerance to cold, fatigue or weakness, poor memory, depression, irritability, weight gain, muscle or joint pain, constipation, decreased libido, infertility, menstrual irregularities or heavy periods, and in more severe cases, hoarseness, decreased sense of taste and smell, mental impairment, skin thickening, and puffy face, hands or feet.
|Other symptoms that may indicate deficiency of Iodine :|
|goiter characterized by an enlarged thyroid gland which may cause a choking feeling or difficulty with breathing and swallowing|
|impaired immune system leading to susceptibility to infections|
|hearing loss in children|
|severe deficiency during pregnancy, breastfeeding or infancy can lead to neuro-cognitive defects in the baby and problems with growth, speech and hearing; a very severe form is cretinism, characterized by brain damage, speech problems, hearing loss, apathy, spasticity, and stunted growth|
|even mild iodine deficiency during pregnancy can hamper growth of the child's brain and lead to low intelligence|
|congenital hypothyroidism is the most common cause of mental retardation in children|
Foods rich in iodine that can help prevent hypothyroidism, and resulting brittle fingernails / brittle toenails, include · salt-water fish · seafood and shellfish · seaweed like dulse, bladderwrack, kelp, nori · iodized table salt.