Biphasic Effect of 1,25-Dihydroxyvitamin D3 on Human Hair Follicle Growth and Hair Fiber Production in Whole-Organ Cultures

In a study from 1994, researchers found that low concentrations (1-10 nM) of 1,25-Dihydroxyvitamin D3 (1,25(OH)2D3) stimulated human hair follicle and hair fiber growth in a whole-organ culture system, increasing growth by 52% and 36%, respectively, with an EC50 value of 0.3 nM. However, at higher concentrations (IC50 value of 100 nM), 1,25(OH)2D3 inhibited growth, which was partly due to a reduction in the growth periods. A significant delay was observed between the onset of inhibition of hair follicle and hair fiber growth. A rapid, transient inhibition of DNA synthesis was also noted at 24 hours with 100 nM 1,25(OH)2D3, which returned to normal by day 4. The inhibition of hair follicle growth required prolonged exposure to 100 nM of 1,25(OH)2D3 for more than 5 hours. The study concluded that 1,25(OH)2D3 might have a physiological role in maintaining hair follicle activity and that high levels could inhibit hair growth in vivo.