**Core Concept**
Oral iron therapy is a common treatment for iron deficiency anemia, where the goal is to replenish iron stores in the body. This concept involves understanding the pharmacokinetics and pharmacodynamics of iron supplements, as well as their clinical applications.

**Why the Correct Answer is Right**
Oral iron therapy works by increasing the absorption of dietary iron, which is then utilized for erythropoiesis (red blood cell production). The mechanism involves the reduction of non-heme iron to its ferrous state, which is then absorbed in the duodenum and proximal jejunum. This process is mediated by the duodenal iron transporter (Dcytb) and the divalent metal transporter 1 (DMT1).

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify a true statement about oral iron therapy. Without further information, we cannot evaluate its accuracy.
**Option B:** This option is incorrect because it is a true statement about oral iron therapy. Oral iron supplements can cause gastrointestinal side effects such as nausea, vomiting, and constipation.
**Option C:** This option is incorrect because it is a true statement about oral iron therapy. Iron supplements can also cause abdominal pain, diarrhea, and dark stools.
**Option D:** This option is incorrect because it is a true statement about oral iron therapy. Iron supplements can also cause headaches, fatigue, and weakness.

**Clinical Pearl / High-Yield Fact**
To minimize gastrointestinal side effects, it is recommended to administer oral iron supplements with food, particularly with vitamin C-rich foods, which can enhance iron absorption.

**Correct Answer: D.**