Vitamin D is critical to hair growth and a healthy follicle because it contains omega-three fatty acids. The omega-three fatty acids ensure that the hair is less likely to become infected at the follicle level. A healthy follicle means healthy hair.
Another way vitamin D helps your hair grow healthy is by stimulating the follicle to encourage hair growth. Vitamin D deficiencies have been linked to hair loss, as well.
Added bonus: research has shown that this vitamin may help create new follicles for hair to grow from.