Which lipid classes are involved in vitamin-related roles (fat-soluble vitamins)?

• A. Phospholipids and triglycerides
• B. Phospholipids and carotenoids
• C. Carotenoids and steroids
• D. Triglycerides and steroids

Answer: (C)

Fat-soluble vitamins depend on lipids not just for absorption and transport, but also for their biosynthesis and function. Carotenoids are lipid-soluble pigments that can be converted into retinal, a form of vitamin A, linking them directly to vitamin A biology. Vitamin D is produced from cholesterol in the skin and is a secosteroid, so it connects to the steroid lipid class. These two lipid classes thus have direct roles in vitamin-related processes, making them the best fit. Other lipid classes shown don’t have as direct a relationship to the formation or function of fat-soluble vitamins.