Question

Which of the following substances is most likely to show a U-shaped dose-response curve for humans, indicating that a very high dose can be harmful but a deficiency also can be harmful?

a) Vitamin C
b) Iron
c) Selenium
d) Fluoride

Answer 1

The substance from the list that is most likely to have a U-shaped dose-response curve in humans is selenium, as it is essential in small doses but harmful in large amounts.

Step-by-step explanation:

The substance that is most likely to show a U-shaped dose-response curve for humans, where both deficiency and a high dose can be harmful, is (c) Selenium. Selenoprotein is synthesized from selenocysteine, an essential amino acid residue important for DNA synthesis, which protects cells from damage and infection and is involved in the reproduction and metabolism of thyroid hormones. Although selenium is required in insignificant amounts, approximately 1 billion people reportedly have selenium deficiency worldwide. In small amounts, selenium is essential for proper cellular function, but in large amounts, it can be toxic and potentially cause cancer. This dual effect, where a substance is beneficial at low doses and toxic at high doses, is what results in a U-shaped dose-response curve.