Cracked Nails: Causes, Treatments, and Prevention- weak splitting nails ,A lotion with lanolin or alpha-hydroxy acid may soothe your nail area. Some people use a layer of clear nail polish to protect cracked nails. To prevent more splits, wear cotton-lined rubber gloves...Brittle Nails, Dull Hair - Signs of Nutritional DeficiencyTake at least 3000 mg of high-quality fish oil per day. Supplement with GLA. Just like fish oil, GLA (gamma-linolenic acid) is another fatty acid that is difficult to obtain from food alone. Borage seed oil contains a high GLA content and can help with dry hair, split ends, and brittle, slow-growing nails. Add 600 mg of GLA daily.