Do your nails
1. split easily
2. Have verticle ridges on them
3. Or are they a spoon shape
If so then you may have a iron difficiency. Or you could be silica or calcium deficient as a lack of either of these vital nutrients can produce dry brittle nails.
If you have small white flecks on your nails it could be that you are Zinc deficient, or that you may have damaged your nail bed in the recent past.
Also, check that you have enough protein in your diet. A good source of protien will supply the body with sulphur, which is essential for nail health.
To correct the deficiencies ensure that you have balanced diet of meat, fish. wholegrain, eggs, seeds, nuts, oils and vegetables. This should help you go a long way towards rectifying the situation.
If, in your family history there are blood relatives that have thyroid problems, then it may be worth getting a blood test, as brittle nails can be a sign of an under or over active thyroid.