Fatty Acids

• A deficiency of fatty acids such as omega 3 can cause a thinning of hair. This can be remedied by taking fish oil supplements or flaxseed oil daily.
  
  

Protein

• On a vegetarian diet, a lack of protein may cause thinning hair. The diet may also cause other deficiencies that may cause hair loss.
  
  

Vitamin E

• Vitamin E in excess may cause various complications involving hair, including hair loss and thinning hair among other things.
  
  

Iron

• Women who suffer from an iron deficiency, though not necessarily anemia, often notice hair loss and thinning before any other symptoms.
  
  

Sudden Diet Change

• Switching diets rapidly may cause the nutrients in your body to react negatively. This reaction can result in thinning hair or hair loss as well as other signs of malnutrition.