NTP Supplement Safety & Efficacy 2 — Questions and Answers
Question 1: Which fat-soluble vitamin poses the greatest toxicity risk when taken in excessive supplemental doses over time?
- Vitamin D
- Vitamin A (Correct answer)
- Vitamin E
- Vitamin K
Correct answer: Vitamin A
Vitamin A (retinol) accumulates in the liver and causes toxicity at doses above 10,000 IU/day long-term, leading to liver damage, bone loss, and teratogenicity.
Question 2: A client taking warfarin asks about fish oil supplementation. What is the primary safety concern?
- Fish oil reduces warfarin absorption
- Fish oil has additive anticoagulant effects and may increase bleeding risk (Correct answer)
- Fish oil inactivates warfarin in the liver
- Fish oil increases platelet aggregation, counteracting warfarin
Correct answer: Fish oil has additive anticoagulant effects and may increase bleeding risk
Fish oil has mild antiplatelet and anticoagulant properties that can potentiate warfarin's blood-thinning effects, increasing bleeding risk.
Question 3: What is the Tolerable Upper Intake Level (UL) for zinc in adults, above which adverse effects become likely?
- 11 mg/day
- 25 mg/day
- 40 mg/day (Correct answer)
- 100 mg/day
Correct answer: 40 mg/day
The UL for zinc is 40 mg/day for adults; exceeding this chronically can cause copper deficiency, immune suppression, and nausea.
Question 4: Which supplement interaction is most clinically significant for a client taking thyroid hormone medication (levothyroxine)?
- Vitamin C taken with levothyroxine reduces its effectiveness
- Calcium and iron supplements taken simultaneously impair levothyroxine absorption (Correct answer)
- Magnesium increases levothyroxine metabolism and reduces its half-life
- Probiotics compete with levothyroxine for intestinal transport
Correct answer: Calcium and iron supplements taken simultaneously impair levothyroxine absorption
Calcium and iron bind levothyroxine in the GI tract, reducing absorption by up to 40%; they should be taken at least 4 hours apart.
Question 5: St. John's Wort is contraindicated with many medications primarily because it:
- Inhibits CYP3A4 enzymes, increasing drug levels
- Strongly induces CYP3A4 and P-glycoprotein, reducing drug efficacy (Correct answer)
- Blocks drug absorption in the small intestine
- Increases renal clearance of most pharmaceuticals
Correct answer: Strongly induces CYP3A4 and P-glycoprotein, reducing drug efficacy
St. John's Wort is a potent CYP3A4 inducer that accelerates metabolism of numerous drugs including birth control, antiretrovirals, and cyclosporine, reducing their effectiveness.
Question 6: A client with hemochromatosis should avoid supplementing with:
- Vitamin C in high doses alongside iron-rich meals (Correct answer)
- Calcium carbonate
- Magnesium glycinate
- Zinc picolinate
Correct answer: Vitamin C in high doses alongside iron-rich meals
High-dose vitamin C enhances non-heme iron absorption and reduces ferric to ferrous iron, significantly worsening iron overload in hemochromatosis patients.
Question 7: Which form of selenium is generally considered safer at higher doses compared to inorganic forms?
- Sodium selenite
- Sodium selenate
- Selenomethionine (Correct answer)
- Selenious acid
Correct answer: Selenomethionine
Selenomethionine is an organic form incorporated into proteins similarly to methionine, with a lower acute toxicity profile than inorganic selenium salts.
NTP Supplement Safety & Efficacy 2
Which fat-soluble vitamin poses the greatest toxicity risk when taken in excessive supplemental doses over time?