This can be a very common sign of thyroid imbalance. Makes sure you check a VERY DETAILED thyroid panel. Nutrients that help are zinc, Biotin ( B9 ) , and calcium. But ... You need to absorb them!
Digestive issues can cause weak , splitting nails. The best calcium supplement for bones and nails is calcium hydroxyapatite . Good luck! In Good Health, Dr Jim Lewerenz . LONGEVITYHEALTHINSTITUTEINC.Com

James Lewerenz