Night blindness is most commonly associated with deficiency of which vitamin?

• A. Vitamin D
• B. Vitamin C
• C. Vitamin A
• D. Vitamin K

Answer: (C)

Night vision in low-light situations depends on rod photoreceptors using the visual pigment rhodopsin, which requires retinal, the aldehyde form of vitamin A. Vitamin A is converted in retinal cells to 11-cis-retinal, which combines with opsin to form rhodopsin. In dim light, rhodopsin must be regenerated after each photon; if vitamin A is deficient, there isn’t enough retinal to replenish rhodopsin efficiently, so rod responsiveness drops and night vision deteriorates. This makes nyctalopia an early clue to vitamin A deficiency. In severe deficiency, you can also see eye surface changes like dry eyes and Bitot spots, but the critical link to night blindness is the role of vitamin A in visual pigment regeneration. The other vitamins don’t participate in this rod phototransduction process, so they don’t explain night blindness.