The term "lipid" encompasses a wide variety of compounds characterized as being insoluble in water but soluble in nonpolar solvents. Which of the following vitamins is not classified as fat soluble?

The term "lipid" encompasses a wide variety of compounds characterized as being insoluble in water but soluble in nonpolar solvents. Which of the following vitamins is not classified as fat soluble?

• A. Vitamin A
• B. Vitamin C
• C. Vitamin D
• D. Vitamin E

Answer: (B)

The key idea is solubility guiding how vitamins are absorbed and stored. Fat-soluble vitamins dissolve in fats and oils, require dietary fat for absorption, and are stored in the liver and adipose tissue, sometimes accumulating if intake is high. In contrast, water-soluble vitamins dissolve in water, are absorbed directly into the bloodstream, and aren’t stored in large amounts—excess is usually excreted in urine. Vitamin C is a water-soluble vitamin. It is polar and rich in hydroxyl groups, so it readily dissolves in water rather than in fats. The fat-soluble vitamins—A, D, and E—fit the lipid-solubility pattern described above, but vitamin C does not. So vitamin C is not classified as fat soluble.

The key idea is solubility guiding how vitamins are absorbed and stored. Fat-soluble vitamins dissolve in fats and oils, require dietary fat for absorption, and are stored in the liver and adipose tissue, sometimes accumulating if intake is high. In contrast, water-soluble vitamins dissolve in water, are absorbed directly into the bloodstream, and aren’t stored in large amounts—excess is usually excreted in urine.

Vitamin C is a water-soluble vitamin. It is polar and rich in hydroxyl groups, so it readily dissolves in water rather than in fats. The fat-soluble vitamins—A, D, and E—fit the lipid-solubility pattern described above, but vitamin C does not. So vitamin C is not classified as fat soluble.