This is what I could find out for you:
In Germany many patients derive benefit from colloidal silicic acid. This is taken by mouth mixed with orange juice. Over a period of two or three months improvement of the nails can be seen.
In Germany, colloidal silicic acid is used for dry skin and brittle nails and is a product that can be bought over the counter. It is available in the UK marketed by a Company called Saguna but it can be quite difficult to obtain. There have been some very limited trials looking at the efficacy of this preparation and these have shown reasonable results.
Anecdotally a number of dermatologists noticed that psoriasis of the nails improved when patients were using vitamin D preparations for psoriasis of their skin. This led to a more focused study of vitamin D creams and ointments rubbed into the cuticle in the treatment of nail psoriasis.
Experience from around the world has shown that this is an effective line of treatment and should be regarded as the first-line treatment of choice. The vitamin D Cream or Ointment should be massaged into the cuticle for about five minutes twice a day. When onycholysis is present, calcipotriol scalp solution can be dripped under the nail and massaged in, which is effective.
Remember that nails grow extremely slowly and what you are influencing is not the exiting nail but new nail that is developing from the nail plate. It may, therefore, take up to a year for finger nails, and two years for toe nails to grow out normally so you must be patient with the treatment.