Q. Which of the following vitamins is generally excreted by human in urine?
Answer: Vitamin C
Notes: Vitamin C (ascorbic acid) is generally excreted by humans in urine. Vitamin C is a water-soluble vitamin. Unlike fat-soluble vitamins, water-soluble vitamins like vitamin C cannot be stored in the body for long periods of time. The human body maintains tightly regulated vitamin C blood levels (around 60–100 micromoles per liter). After absorption, vitamin C in excess of bodily needs is excreted daily via urine in order to maintain homeostasis. People with adequate vitamin C status excrete significant amounts of vitamin C in urine. A daily intake of 100–200 mg is considered adequate to saturate body stores in healthy adults. Higher intakes above the saturation threshold produce proportionally higher levels of urinary vitamin C excretion. Thus, vitamin C is readily filtered by the kidneys and excreted in urine when body levels exceed saturation. This makes measurement of urinary vitamin C a useful biomarker for evaluating vitamin C intake and status.