## **Core Concept**
The question revolves around the recommended maintenance dose of vitamin D for breastfed full-term infants. Vitamin D is crucial for bone health and development in infants. Breast milk, although ideal for infants, often does not provide sufficient vitamin D, necessitating supplementation.

## **Why the Correct Answer is Right**
The American Academy of Pediatrics (AAP) and other international guidelines recommend a vitamin D supplement for breastfed infants. For full-term infants, a dose of **400 IU (International Units) per day** is commonly advised. This dose helps maintain adequate vitamin D levels, supporting healthy bone development and reducing the risk of deficiency-related conditions like rickets.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Lower doses (e.g., 100 IU/day) are generally considered insufficient for maintaining optimal vitamin D levels in breastfed infants.
- **Option B:** While 200 IU/day might seem reasonable, it is not the universally recommended dose for the maintenance of adequate vitamin D levels in breastfed full-term infants.
- **Option D:** Higher doses (e.g., 1000 IU/day) might be considered for specific cases of deficiency but are not standard for maintenance in otherwise healthy, breastfed full-term infants.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the recommended dose can vary slightly by organization but **400 IU/day of vitamin D** is widely accepted for breastfed full-term infants. This dose is critical for preventing vitamin D deficiency and ensuring healthy growth and development.

## **Correct Answer:** . **400 IU/day**