An element that is considered a non-essential nutrient is which of the following?
**Core Concept**
Non-essential nutrients, also known as conditionally essential nutrients, are compounds that can be synthesized by the body under normal conditions but may need to be obtained from the diet during times of stress, illness, or rapid growth. These nutrients can be produced in sufficient quantities by the human body when all required enzymes and substrates are available.
**Why the Correct Answer is Right**
Selenium is a non-essential nutrient because the human body can synthesize it from the essential amino acid methionine. The enzyme selenocysteine synthase catalyzes the conversion of methionine to selenocysteine, which is then incorporated into selenoproteins. However, in cases of severe illness or when the body's demand for selenium exceeds its production capacity, dietary intake becomes necessary.
**Why Each Wrong Option is Incorrect**
**Option A:** Nitrogen is an essential nutrient, primarily obtained from dietary proteins, and is necessary for the synthesis of amino acids, nucleotides, and other biomolecules.
**Option B:** Fluoride is an essential nutrient that plays a crucial role in the development and maintenance of healthy teeth and bones. It is obtained from dietary sources and is also added to community water supplies in many areas.
**Option C:** Iodine is an essential nutrient necessary for the production of thyroid hormones, which regulate metabolism, growth, and development. It is obtained from dietary sources, such as iodized salt, and is essential for preventing iodine deficiency disorders.
**Clinical Pearl / High-Yield Fact**
Non-essential nutrients can become essential during times of stress or illness, highlighting the importance of a balanced diet and adequate nutrient intake to support optimal health.
**Correct Answer:** D. Selenium.