Deficiency could be either shortfall from the diet or poor absorption in the gut.Check for this first.
Next Steps
Maintain a food diary for atleast 7 days by trying to include wide variety of foods.This will serve 2 purpose 1. Whether you are actually consuming the nutrient rich food. 2. Whether the required amounts of nutrients are taken?
Health Tips
Till you figure out the food sources, it is better to take the supplements, so that there is no further reduction in the levels.Hope this helps