However, in those who do not get enough of these sources of the vitamin, rickets may develop as a sign of the deficiency. Other signs of Vitamin D deficiency include a reduction in calcium absorption and hair loss. Vitamin D deficiency causes hair loss through a disruption of the hair growth circle. The deficiency shortens the anagen phase and prolongs or speeds the onset of telogen and catagen phases. To reverse hair loss due to Vitamin D deficiency, you need more exposure to sunlight especially early in the morning.