I found this information:

Nail problems, any changes or abnormalities, are often the result of nutritional deficiencies or other underlying conditions. It is said that nails can reveal a great deal about the body’s internal health.

Here is a list of some of the changes in the nails and nutritional deficiencies that caused them:

Hangnails: caused by lack of protein, folic acid, and vitamin C.

White bands across the nails: also protein deficiency

Dryness and brittleness: lack of vitamin A and calcium

Fragility, with horizontal and vertical ridges: deficiency of B vitamins

Excessive dryness, very rounded and curved nail ends, and darkened nails: insufficient intake of vitamin B12

“Spoon” nails (nails that develop a concave shape) and/or vertical ridges: Iron deficiency

White spots on the nails: Zinc deficiency

Fungus growth around the nails: Lack of sufficient “friendly” bacteria in the body

Splitting nails: a lack of sufficient hydrochloric acid (HCL) Also, cuts and cracks may indicate a need for more liquids. Two tablespoons of brewer’s yeast or wheat germ oil daily helps with splitting nails and or hangnails.

It has been suggested that soaking your nails about 10 to 20 minutes a day in olive oil or apple cider vinegar will strengthen your nails.

Important nutrients that can help clear up the nutritional deficiencies would be:

Acidophilus inhibits harmful bacteria that causes fungai infection
Rejuvelac also introduces friendly bacteria for digestion (recipe is on this site)

The neat thing about the herbs I’m going to suggest is that not only do they have vitamins and minerals that you need but they also detoxify the system.
Yellow dock is especially good for nails, it provides calcium, iron, potassium and many B vitamins and vitamin C and many other minerals. It is a great blood purifier and cleanser and improves colon and liver function.

Two great Hair, Skin and Nail herb combinations would be:
1. Kelp, Dandelion, Alfalfa
2. Dulse, Horsetail, Sage, Rosemary. (Horsetail or another name for it is Shavegrass that has natural silica that converts into calcium in the body)
These formulas are high in minerals for improvement in hair, skin, and nails

You can buy a large container of Alfalfa tablets at the Health Food store put out by Bernard Jensen that will give you vitamins, minerals as well as enzymes to help digest your food. I take as many as 12 a day and also notice added energy and better digestion and bowel function.