Final answer:
Vitamins are classified as micronutrients due to their presence in small amounts in the body and in food, as well as their small requirements. However, the idea that small amounts of food are sufficient to meet vitamin needs is not a reason.
Step-by-step explanation:
Vitamins are classified as micronutrients because they are present in the body in relatively small amounts and in food in small amounts. They have requirements that are relatively small. However, the statement 'You only need to eat small amounts of food to get an adequate supply of vitamins' is incorrect, and therefore not a reason why vitamins are classified as micronutrients.