10 Ways Your Body Is Telling You You’re Running Low on Key Vitamins

“Thin, brittle hair” Possible deficiency: B vitamins You hear all about how important the B vitamin biotin is for strong, healthy hair, and that's true. However, running low on folate (also called folic acid) may also cause thin, brittle strands, says Small. Folate is often found in enriched grains like bread and cereal. Even one cup of white rice is an excellent source..