**Core Concept:** Iodine is an essential trace element for human health, particularly for the synthesis of thyroid hormones in the thyroid gland. Iodine deficiency disorders (IDD) can lead to numerous health complications, particularly in pregnant women and children.

**Why the Correct Answer is Right:** The correct answer, C, states that "Approximately 1.1 billion people worldwide suffer from iodine deficiency". This highlights the global prevalence of iodine deficiency, which is a significant public health concern.

**Why Each Wrong Option is Incorrect:**

A. This option mentions "100 million" which is much lower than the correct number and does not represent the actual global burden of iodine deficiency.
B. This option refers to "18 million", which is a much smaller number than the actual prevalence of iodine deficiency.
D. This option states "500 million", which is still much higher than the correct number, but closer to the actual burden compared to option A.

**Clinical Pearl / High-Yield Fact:** Iodine deficiency disorders can lead to various health issues, including goiter, hypothyroidism, cretinism, and mental retardation. Addressing iodine deficiency is crucial for preventing these complications and improving global health outcomes.

**Correct Answer:** C. Approximately 1.1 billion people worldwide suffer from iodine deficiency.