Biotin, a B vitamin, is known to strengthen hooves in animals. As a result, Swiss researchers investigated the use of biotin in strengthening brittle fingernails in humans, despite the fact that it remains unclear exactly how biotin affects nail structure. An uncontrolled trial of 2.5 mg biotin per day found improved firmness and hardness in almost all cases after an average treatment time of 5.5 months.¹ In a controlled trial using 2.5 mg of biotin per day, women with brittle nails, who had their nail thickness measured before and at six to fifteen months after, found their nail thickness increased by 25%. As a result, splitting of nails was reduced. In an uncontrolled study of people who had been taking biotin for brittle nails in America, 63% showed improvement from taking biotin.² Although the amount of research on the subject is quite limited and positive effects do not appear in all people, those people having brittle nails may want to consider a trial period of at least several months, using 2.5 mg per day of biotin.

Gelatin has been marketed as a remedy for brittle nails since the turn of the twentieth century and has been mentioned in medical journals at least since the 1950s.^3,4,5 Gelatin is a slaughterhouse byproduct, made from the hooves and other inedible connective tissue of cows. While some people claim success using gelatin to strengthen brittle nails, others claim that the remedy is ineffective,^6,7 and that the real cause of brittle nails is lack of moisture, not protein deficiency.

One doctor has observed that supplementation with glucosamine sulfate (amount not specified) can increase the growth rate and strength of fingernails and toenails;⁸however, no controlled trials have been done.

Anecdotal reports suggest that horsetail may be of some use in the treatment of brittle nails.⁹ This may be due to the high content of silicic acid and silicates in horsetail, which provide approximately 2 to 3% elemental silicon.