## **Core Concept**
Keshan's disease is a congestive cardiomyopathy caused by a combination of dietary deficiency and a specific strain of *Coxsackievirus* B. The primary dietary deficiency associated with this condition is of **selenium**, an essential trace element.

## **Why the Correct Answer is Right**
Selenium plays a crucial role in the body as an antioxidant, primarily through its incorporation into **selenoproteins**, which include enzymes like glutathione peroxidase. This enzyme helps protect cells from oxidative damage. In regions where selenium levels in the soil are low, such as certain parts of China where Keshan's disease was first identified, the dietary intake of selenium can be significantly reduced. This deficiency, combined with other factors like viral infections, can lead to the development of Keshan's disease. The mechanism involves impaired antioxidant defenses leading to myocardial damage.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because while vitamins are crucial for overall health, Keshan's disease is specifically linked to a mineral deficiency rather than a vitamin deficiency.
- **Option B:** This option is incorrect as there is no well-established link between Keshan's disease and a deficiency of this particular substance.
- **Option D:** This option is incorrect because, although important for health, the condition in question is specifically tied to selenium deficiency.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that Keshan's disease is one of the conditions associated with **selenium deficiency**. Another condition related to selenium deficiency is Kashin-Beck disease, which affects the joints and bones. Selenium deficiency can lead to impaired immune function and increased susceptibility to infections.

## **Correct Answer:** C. Selenium.