Does Vitamin B12 Cause Dark Yellow Urine?
No, vitamin B12 supplementation does not cause dark yellow urine. This is a common misconception—the culprit is actually riboflavin (vitamin B2), not B12.
The Real Cause: Riboflavin (Vitamin B2)
- Riboflavin (vitamin B2) is responsible for yellow-colored urine when consumed in supplemental doses, as documented in the ESPEN micronutrient guidelines 1
- This color change is harmless and occurs because excess riboflavin is rapidly excreted in urine, giving it a bright yellow or fluorescent appearance 1
- Research confirms that vitamin B2 supplementation at approximately 200× the recommended dietary allowance significantly alters urine fluorescence and color, while vitamin B12 does not 2, 3
Why B12 Does Not Change Urine Color
- In controlled studies where healthy volunteers received vitamin B12 at 200× the recommended dietary allowance while maintaining euhydration, urine color remained unchanged despite elevated urinary B12 concentrations 2
- Specifically, urinary B12 concentration increased dramatically (from 8.6 × 10⁴ to 5.7 × 10⁶ nmol/L), yet urine color scores did not differ between supplemented and non-supplemented trials 2
- Fluorescence spectroscopy studies demonstrate that only vitamin B2 shows noticeable influence on urine fluorescence spectrum; vitamin B12 and other tested vitamins do not 3
Clinical Implications
- The yellow urine commonly attributed to "B vitamins" or multivitamins is specifically due to riboflavin content, not B12 1, 2
- This distinction matters clinically because urine color remains a valid hydration assessment tool even with B12 supplementation, but may be confounded by B2 supplementation 2
- Urinary excretion of vitamin B12 is primarily dependent on urine volume rather than intake, further explaining why it doesn't alter urine appearance 4