Question: what vitamin are you lacking if your hair is thinning?
Answer: This vitamin is necessary for keeping hair healthy. Alopecia, a condition in which hair falls out in small patches, is one possible symptom of niacin deficiency ( 41 , 42 ). Biotin (vitamin B7). Biotin is another B vitamin that, when deficient, may be linked to hair loss ( 34 , 43 ).