Susan Johnston of NaturallyCurly writes;

You’ve finally learned to love your curls . . . and now you’ve noticed those once-lustrous locks are thinning. Oh, the injustice! Don’t despair—we’ve compiled five tips to keep you and your curls looking chic and stylish at any age.

1. Rule out a medical issue.
While everyone’s hair thins a bit with age and thinning hair can be genetic, it can also be a sign of a medical issue like anemia or thyroid problems. Debra Jaliman, MD, a New York City-based dermatologist, recommends asking an endocrinologist or dermatologist to rule out these issues. “Most medical doctors are not the ones to rule out medical issues. A dermatologist or endocrinologist would be the best medical experts to go and see,” she explains. A poor diet may also contribute. Fortunately, “if you lack iron and start eating red meats then the hair will regrow once your diet is appropriately balanced,” says Jaliman.

2. Consider Biotin supplements.
According to Jaliman, biotin supplements (also called vitamin H for “Haar and Haut,” which mean “hair and skin” in German) can help thicken hair and strengthen nails. Though biotin occurs naturally in some foods, few food sources are rich in the vitamin, so during the 1940s, Swiss scientists developed a synthetic process to replicate it. Biotin supplements are now available over the counter, and Jaliman says they are extremely effective.