When your body doesn’t get enough vitamin D, it can affect your hair. The cells that play a role in your natural hair growth cycle, called keratinocytes, face difficulties in doing their job.Having lower levels of vitamin D seems to make the phase when your hair grows shorter, and the resting phase longer. Also, the layer under your skin that supports your hair, called the dermic layer, becomes weaker, making your hair more likely to fall out.Not having enough vitamin D is also connected to certain health conditions, like alopecia areata. This condition causes small bald patches on the scalp and sometimes the beard.